Installed a 997 GT3 Master Cylinder in my 996 C2

I installed a 997 GT3 brake master cylinder on my 996 today. I had tried several things but none made any significant difference in reducing what is IMO excessive pedal travel and squishiness during hard braking. Slakker here on the forum suggested the 997 GT3 master cylinder as a solution so I put one in today. WOW what a difference. Now the brake pedal feels like a Porsche should. While this seems to be a very popular upgrade on the Cayman forum I was surprised that little to nothing is posted on the 996 forum about this upgrade, so here are some notes from the install. The part number for the 997 GT3 M/C is 997-355-910-30 and you can buy a TRW version (OEM supplier) for just over $200 from various suppliers. The cross reference TRW part number is PMN166, but you can still find it under the Porsche part number. Stock master cylinder size on the 996 is 23.8mm on the C2/early C4 and I think the C4S/Turbo and the 996 GT3 are 25.4mm stock. The 997 GT3 M/C has a 27mm bore. The 997 GT3 M/C has two M12 outlet ports. Depending on your year and options of your 996 you either have two M12 lines or one M12 (front channel) and one M10 (rear channel) line. My car is a 2003 C2 with PSM and it had one M12 and one M10 line. This means that if you have the M12/M10 setup you have to convert the rear channel to M12 somehow. Options to deal with the smaller M10 rear channel line is to use and adapter, or make a new line. Making a new M12 line is easy if your car is one that has the PSM booster pump located just below the M/C as the line is only a few inches. My car has the remote mounted PSM booster pump way over on the passengers side so making a new line involves alot of bending so I elected to use an adapter. I found that there are two main M10/M12 adapters out there on the market, one made by Dorman and one made by AGS. Both have a bubble fitting on the male M12 end, but on the inside M10 female end they are milled to receive an SAE fitting, not a bubble (european) fitting going in. I found that the Dorman adapter was a bit deeper on the M10 female portion than the AGS, so the Dorman one is the best one to use as it will engage the most threads. I mounted the adapter under my drill press and using a 21/64" bit modified to cut brass, running at high RPM (2300) I turned the SAE female M10 internal surface into an internally tapered bubble (euro) surface. (You can Google how to file a drill bit for cutting brass w/o gouging.) This worked out great and everything bolted up really nicely. I tested with very hard pedal pressure (standing on the brakes) several times w/ no leaks. If you have the skills to do this it makes the install easy and the resulting reduced pedal pressure and travel is excellent! Photos attached....

Thanks for sharing....definitely something I would consider.

If there ever is a sticky for track-support mods, this needs to be included. Thanks for sharing. I'm right at the cusp of having to address this

Good info. Thanks Nickshu!

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You bet guys! This is a pretty easy mod. Aside from getting the adapter setup it only took me about 1 hour to install and another hour to bleed. And on top of that it's a pretty inexpensive mod. Again I am surprised that there has not been much discussion about this on the 996 forum, the Cayman guys have been all over this upgrade for awhile now. We had a few inches of snow today...I usually don't drive my car in snow, but couldn't resist....so I took it around the neighborhood, mostly sideways, and gave the PSM and ABS a good workout. No issues noted with the upgraded M/C and any of the PSM/ABS electronics. Just a way better pedal feel and much less travel. I may have to adjust my adjustable Rennline gas pedal up a bit for heel and toe now. Aaaah champagne problems.

Hi, Any updates on this now that you've had it installed for a while?

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Yes... No issues at all. Working great and the pedal feels awesome!

glad i saw this i purchased one a few months ago thats still sitting on the shelf, but didnt realize i may need an adapter, i have a 2000 C2 any idea if its needed? if not i will take your advice and order an adapter

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I am not sure. I think perhaps the cars with PSM have the smaller M10 rear circuit and the cars without have double M12's. It's easy to pull off the master cylinder cover and take a look, the size of the fittings is obvious under direct visualization.

tks i will have a look

just out of curiosity, would the 996 turbo or 997 turbo m/c mount up with less machining? I can attest that the 996tt stops like a beast, far better than the 996 n/a that I had did.

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I saw threads on another Porsche forum where they needed and adapter on turbos as well. I am thinking that cars with PSM had the smaller rear channel but have not confirmed. The 996 Turbo and 997 Turbo still has a smaller M/C than the 997 GT3, but yes larger than the N/A models. On the 996 the C4S, Turbo, and GT3 used the same master cylinder. On the 997 the GT3 got a larger master cylinder than the 997 turbo, S, etc models. For sure there is more to stopping than just the M/C...caliper size, rotor diameter, pad area, etc. My main goal was to get rid of the squishy feel to the stock 996 brake pedal, which for me (and others if you read old posts) I could not get rid of with bleeding, SRF brake fluid, etc. I found it especially bad on the track at high temps. With the 997 GT3 M/C the pedal feels like a Porsche should. Rock solid and short travel.

I'm not a fan of the stock 996 pedal feel. Will definitely consider this! Thank you for sharing!

I ended up using a 996 turbo one when I upgraded my front brakes to 390mm and the rears to 350mm on my 99. I had to set up adapters but, I didn't have to do any drilling for it to seal. I found all the proper adapter fittings. I think through ebay. If anyone has a question of if they actually have a 997 gt3 MC you can verify that with those two machined dots on the master cylinder near the reservoir. I'll have to switch to the 997 whenever I come across another one that is cheap. I already have one in my 987.

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what did you use to get the rotors that large? i assume some pre made big brake kit? or did you find some cheaper solution?

AutohausAZ AZ has these master cylinders on sale for 183.47, normally $191, good deal!

Thank you so much Nickshu for this Five Stars Topic. And thanks a lot to Quadcammer that posted in my topic, the reference on yours. I come from the 986 “chapter”, and have the exact same problem, i.e.: hate the “mushy brake pedal” feel of the OEM car. (The only positive things of it, ..is the feeling that you have to bleed every track days !) Note: I have Brembo big brake kit on my Boxster (large floating rotors and 6 pistons calipers) and just want a FIRM (normal sport car) brake feel. I also got the feeling that the large calipers even made the feeling a little bit worse than the original ! By the way, ..after 30 years non stop of multi 911 (including 11 years of 996), you could not believe how great I feel about a Boxster. Nothing beat having the engine at the right position ! (..or: why I’m on the “986 Chapter” !) After going for an install process of a TRW PMN166, ..I found the mismatch on outlet tubes ! (or, good for back to OEM and ..another full bleeding session !) Thanks again, I think I may also go on adapter solution too. (Or trying to get another line new or from a dismantler, and cut the bubble, remove the 10mm nut, to replace it by a “small” tube 12mm nut (made for 4.6mm tube) (the “common” 12mm nuts seems to be designed for 5.8mm tubes) and rebuild the bubble. This later solution would have the advantage to suppress the need of an adapter. By the way, about this upgrade, I also observed during this tentative that the mounting of the GT3 M.C. on the booster is different at the level of the sealing between the booster and the MC : on the OEM MC, at least on the 986, the sealing is done the “axial way” with an O-Ring, while on the “GT3” one, the sealing is done in the “vertical plate”, facing the booster. It seems to me that the sealing of the “GT3” model is much more logical ! Did you also found this difference on the 996 ? (or is this “typical” to the 986 ?) Sorry for off topic, but for curiosity: a photo of my front brakes (sure, also PSS9) :

By the way, about nice and easy mods, a simple one to try to help to keep brakes as cold as possible is OEM GT2 air ducts. Available as Porsche parts (number on the photo) cost about 30 bucks and real easy to install (replace much smaller ones) !

..back on topic : Btw, two comments : a) Strange, on the list of cars, ..it do not says GT3 for the PMN166 !!!! b) It looks like “Brake Hoses Unlimited” on eBay has “THE” adapter :

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Just curious, did you bench bleed the 997 master before installing in your car?

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No I didn't. Just pressure bled with my Motive bleeder. No issues. Have done it that way three times now on two different cars with no problems.

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Yes that looks like the perfect one. I searched all over and couldn't find one like that. Cool!

subbed.. this looks like a great option in my 99 C2..no PSM or anything, so I'm hoping it's an m12 front and rear port., I'll have to look at it after work... but with that adapter, either way is a breeze. 997 GT3 BMC is going on the list. Thanks for the how-to

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A link would be nice - can't seem to find brake hoses unlimited on Ebay... Thx

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Is this it? http://www.ebaystores.com/BRAKE-HOSES-UNLIMITED

Adapter: https://www.ebay.ca/itm/Brake-Line-T...UAAOSwZVJaxivb Here is the seller I found: https://www.ebay.ca/usr/goodbrakes?_...p2047675.l2559

This looks like the adapter, right? https://www.ebay.com/itm/Brake-Line-...item4d353a6340

Just found this master cylinder on FVD Brombacher for $175.00 plus $15.00 shipping. Best price I have seen.

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Sorry, you are right : The easiest (on ebay) : eBay item number: 331605500736 The description line (title) is "Brake Line Thread Adapter, Male M12 x 1 Bubble, Female M10 x 1 Bubble" and the vendor id is goodbrakes ( 14647 ) (100% Positive feedback)

I cannot wait ..to have REAL brake feeling on my 986 ! Thanks a lot for all the good info provided here.

Someone posted this on the GT3 forum...if you have a Non-PSM car you can buy the Boxster line that goes from the rear M/C port to the ABS unit and avoid needing to use an adapter. The Boxster line is the same as the 996 Non-PSM line but is M12 for the rear port instead of M10 so it eliminates the need for an adapter. Does not work for PSM (Please Save Me - LOL-) cars. Here's the post: https://rennlist.com/forums/996-gt2-...l#post15301049 The part number for this line is 996 355 313 04. I ordered one and installed on my non-PSM GT3 without any issues.

Hi guys, for anyone looking to do this upgrade, there seems to be a world wide shortage of the TRW MN166 Master Cylinder! I have tried all the usual online suppliers and there is zero stock! Any ideas where I could maybe try?

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Take the hit and buy from Porsche for $500+ appears to be the only option currently. I tried to buy one on Ebay only to be messaged by the seller that they were sorry they forgot to take the auction down b/c there is no stock left on the TRW part. Bummer.

By the way, I confirm that is is easy to find a M12 bubble nuts built for 4.6mm tube. (The M12 bubble nuts that we have on our cars are set on 5.8mm tubes.) So, if you can get the OEM brake line that goes from the rear outlet of the master cylinder to the PSM booster pump, then : by cutting the bubble at one end (loosing only about 1/4 of an inch), and replacing the M10 bubble nut of the master cylinder side nut by a m12 nut (built for 4.6mm tube), and rebuilding the bubble, ..then you will have a tube assembly that will let you forget about the need an adapter ! Or, we have two solutions : adapter or re-building a taylor made tube with an M12 bubble nut at one end and the M10 at the other end !

Install done : such an INCREDIBLE improvement. Would like to thank you Nickshu, the info in your post made the install easy. Now, I have the feeling that I have real good brake.

this is a direct fit without any adapters on a 2000 C2 without psm i just did it, the pedal feels so much better it reminds me of the 991 GT3 feel

Help!! I fitted the MC (PMN166) and the ABS and PSM lights along with error 4460 came on. I refitted the original MC and the warnings went away. All this was done at Porsche and was correctly bled using PIWIS and the valve behind the headlight. I then replaced the brake switch with 2 original Porsche switches and 2 Facet switches, still the ABS/PSM lights come on. I also fitted a new Mass Airflow Sensor, lights still come on. Upon further research I found that no one has reported a successful installation on a Carrera 4/Turbo, whereby the lights do not come on. Does anybody know of this being done successfully on a Carrera 4/Turbo?

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Im assuming my '99 would be a direct swap as well? Really looking forward to doing this swap since I'll be replacing my brake lines with some stainless braided lines... cant wait to feel the difference. Edit: Anyone know where the TRW part is in stock? cant find it anywhere. Pelican shows it instock but when you add to cart it redirects

I looked a couple of months back and gave up. Hoping they'll show up sometime and I'll grab one. Let me know if you find a stash somewhere.

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Is it the GT3 master cylinder you are talking about? Are they NLA?

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No one had the TRW version in stock. Porsche had them, but they're a lot more expensive.

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I believe you can buy them from Porsche, just can't currently get the TRW version (exact same thing just not in a Porsche box). Of course double the price from Porsche.

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Yes, I have the exact same problem. I changed the brake switch and cleared the 4460 error, (that came up in intermittent ways). Too early to say if problem solved or not yet, ..but still, thinking about the overall situation : Whoa, I'm impressed, in and out MC, ..this is a lot of purging ! I'm curious : How much time the local Porsche dealer is charging you to do a complete "Piwis purging" ? About this specific problem, I think the source is the sync between the "brake on" signal (sensor is the brake switch, a 20 bucks part) and the pressure sensor (I think located in the ABS pump assembly, ..that is a multi thousand bucks part). It looks (to me ?) like in the ECU logic, if the pressure sensor is up to a threshold level before (too early) the brake on signal, the ECU do trigger the error 4460. It is probably also the same, ..if the opposite situation happen. I never seen the ECU code, but this looks to be logical steps ! (Remember (joke), the ECU code is quite "sophisticate" : It can even check that a car has open "hood", steering wheel not moving for a certain time, etc.. to then decide to change some fuel intake quantity, thinking that these conditions are like that someone may be putting a probe in the exhaust pipe ) Back to serious: I think it is a question of adjustment and timing sync between the switch action and pressure (level/threshold) detection. I'm not sure at 100% yet if the switch should be "longer" or "shorter", ..but I guess, as with the new MC, the pressure building up "faster" (or "earlier"), the switch seems to tend to send "brake on" signal "too late" and have the ECU "thinking" that there is a pressure problem (pressure up before brake switch on ???), ..or : the switch (if my logic is correct ??) is "too long" and should be shorter. Still, the brake feeling with this type of MC is absolutely great (so much better than the OEM feeling). Worse to investigate further in order to find a solution that is technically correct. (We are talking about a 20 bucks parts, that is "relatively easy" to excahnge (beside the non comfy mode, that requires to put our head, ..where we normally put our feet !!!) Can even use the previous ("old switch"), shorting it a bit and retest ! Well, one thing seems to be quite clear on your experience : in your case, it is not a problem of "The" pressure sensor !

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I spent years on this issue and never found a work around. The OEM master cylinder has a special bypass circuit in it that is required for the PSM system to function. I think it is a bypass that allows the PSM system to build pressure when the brake pedal is not applied. With an incompatible MC, you can not pass the PSM readiness test (because no pressure builds at the sensor) that occurs each time the car starts and first exceeds about 30 mph. When that happens, the 4460 error is set. I had to go back to the stock MC to fix the issue. So, you have a choice... Great brake feel with an incompatible MC or a PSM/ABS system that works. Since I drove my car for years without PSM, I would probably vote for the better braking if doing it again (but I spent $500 on the stock MC). You don't "need" PSM/ABS, though many like the sense of security it provides. Of course, don't expect to sell your car without working PSM/ABS... If someone can find a compatible MC with a larger piston, that would be ideal. Anyone have a contact at TRW? We want a 27mm piston with a bypass (or without one -- I'm not sure -- basically same as 99635591050, but larger piston)...

Thanks a lot for your post @jpurban, VERY interesting. Have you been able to understand what is the "special bypass circuit" that you mention as present in the OEM MC (and not in the TRW PMN166) ? Did you tried to contact TRW in order to get some deeper explanations ? (Looking at TRW, I just learnt that in 2015, ZF (German transmissions Co) did acquired TRW !)

I just sent an e-mail to TRW, but I'm not expecting much... I guess I'm cynical -- Corporate customer service usually disappoints, right? We really need to talk to a TRW engineer with access to their MC specs/design sheets. I came to the "special bypass" conclusion by accident... I was trying to bleed my PSM system manually using a 12V source to power the PSM boost pump (Who needs a PIWIS? Forget about the non-functional Durametric.). With the GT3 MC, it only worked when the pedal was partially depressed (blocking the bypass). When the pedal is not engaged, the PSM pump tries to build pressure, but the fluid just circulates via the "standard" bypass circuit in the GT3 MC. That is the source of the error -- no pressure builds. So, we actually need a MC without a standard bypass circuit. We may be out of luck because I suspect a "no bypass" design would be a safety hazard in a non-PSM system. I suspect PSM has a built in bypass function outside of the MC. So, I doubt many options would exist, except for those other MC that are also used in a PSM-like application. I could be wrong, but this is my current working hypothesis, for whatever that is worth.

Thank you GVA-SFO and jpurban, the bypass makes perfect sense, especially with regards to pressure build up (or lack thereof) I will be taking the Carrera back again tomorrow for further investigation, I might have to refit the original MC, which would be painful as the GT3 MC has such great feel! Will let you know the outcome.

https://rennlist.com/forums/parts-ma...stock-trw.html Price gouging?

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Not really considering they are over $500 from Porsche.

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The link is for the TRW part. If it was $350 for the "Porsche" part i'd grab one up

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They are identical parts, Porsche's are made by TRW. You just pay the premium to have a Porsche part number stamped on it and to have it packaged in a Porsche box. I do get that some people prefer the Porsche branded stuff.

Also, Aaron (the guy at Rennpart) is a good guy. I find it hard to imagine him "gouging" anyone. He's always treated me very fairly, gives good prices, is very communicative, and packs stuff well/securely. He's an enthusiast, and active member of Rennlist too.

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I understand this. I'm just saying that not long ago, they were around $200-250 for the TRW part and ~$450-500 for the Porsche Part. This is the TRW part thats ~$100 more than it was not long ago Im sure he is, and im all about capitalism... but im also a cheapskate LOL Too many projects to be handing out extra hundreds if I can avoid it. I sure wish I got my ROW 030 suspension kit for $900 back in the day as opposed to the $1200 I paid for it about a month ago. If this is the new price for the M/C, I'll pay it eventually but i'm still hoping for a deal

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Agreed. Basic supply and demand. There is low supply and high demand. Aaron would be a bad businessman not to up the price a little bit.

Does anyone know if error 4460 is limited to PSM equipped cars? Nickshu, did you get this error on your 996.2 (iirc) car?

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I had no error messages on my 2003 Carrera 2 with PSM when using this master cylinder. None at all. Searching here the problem seems to be with Turbo cars. The PSM pump location is different on Turbos...it's right under the master cylinder. On my C2 the pump was over on the passenger's side of the frunk. Not sure if the system is different or just the location of the pump but that could indicate some sort of difference in the two systems.

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Anyone that needs a TRW master give me a call directly, I have two left. Yes the price is a bit higher, but I haven't been able to get them in the past several months and actually needed one for a GT3 in the shop recently so I don't want to give them away. Not sure when more will come in as they're still on BO with TRW. Often times when this happens the price ends up going up, recently they've been blaming it on "tarrifs."

@jpurban, about error 4460 and bypass : I'm still thinking and to tell you the truth, I'm not yet to the full understanding point about the "bypass" issue ! The ABS ECU is triggering the Error 4460. What are the possible sources (sensors) involved to have the ABS ECU triggering this error ? In my current understanding, there is the brake switch sensor, and there is the pressure sensor, ..that is located inside the PSM pump assembly. What I’m missing in this decision chain ??? Most probably the reading of the 4 wheels sensors (rotation speed of each wheels), but I doubt these are involved or are at the source of our specific problem. (Btw, I wonder what would be the error code if one of the wheel sensors would fail.) Also, I do not think that the pressure sensor is sending “analog info”. I think this pressure sensor gives an “off/on” info, and this, according to a threshold level. (But, ..I may be wrong on that !) Anyway, even if it would be an analog info, I do not think this would have effect in “our” case. I.e.: if the GT3 Master Cylinder would give more pressure, than the OEM MC, Btw, this would easily trigger the ABS on every braking ! The larger piston should give more quantity of fluid on the move, but, the pressure should remain about the same, ..this for sure, until you apply a brake pressure to a level that would then trigger the ABS. (Which, in my case never did happen when I have the 4460 error (seen in this case with dash board: ABS and PSM lights on)! So, at my current understanding level, the amount of pressure is not the problem, but the buildup of the pressure (our perception that the braking point is firm and efficient) that happen to be much more earlier in the travel (position) of the brake pedal. I think in the ABS/PSM ECU, the function diagram for a normal operation should be : first, to see brake pedal action, i.e.: brake light on, and then, “a bit” later, pressure building up, that do trigger pressure sensor above the threshold level. To my understanding, in the 4460 error seen in our cases, I still think that the ECU get the “brake on” too late, i.e.: the ECA sees that there is already pressure reading from the sensor, ..or: ..thinking that something is wrong with the pressure sensor (i.e.: error if pressure is up, ..when brake pedal is “off”, or the ABS (or PSM) pump is generating a pressure when it should no. If there is a kind of bypass in the master cylinder (or in the PSM assembly), I can only think that this should just delay the pressure build up. I do not think that there his another sensor that would read specific information from a bypass circuit. Or : at this point, I would still think that the ECU when checking these two info, is not happy if the pressure if up too early versus the pedal position, taken from the brake switch ! The fact that the PNM166 has a larger piston, it is very clear that the pressure build up earlier in the travel position of the piston. And, to me, it seems logical that If we have “pressure” on, before “brake on”, this situation should trigger an error. I'm still not 100% sure of the above theory. In the mean time, I will try to trim one of my two brake switches, in order to try to verify the above.

@GVA-SFO, The 4460 error is related to the analog voltage of the brake sensor on the back of the ABS unit (not the PSM boost pump). The sensor has a value of about 0.6V at 0 psi. The non-zero voltage allows the system to verify the sensor is present during initialization. At max pressure, the voltage is about 2.2V, about 3,000 psi, if I recall correctly. The brake light switch is a binary switch, open or closed. If it fails to close the circuit by the time the ABS pressure sensor is reading a materially higher voltage, an error is set. This sets a 4460 error. It is corrected by making sure the adjustable plunger is set properly (usually) or replacing the switch once the internal contacts wear out. If you think this is the reason the PMN166 sets the 4460 error, then test it yourself. Start your car, but don't drive it. Repeatedly press the pedal slowly and see if the error sets without exceeding 30 mph. I've done this while monitoring the pressure voltage and the stop light activation -- no error sets. So, I don't think the issue is related to the brake/stop light switch. This is confounded by the 4460 error set during the PSM boost pump check. The PSM boost pump check is done after start, vehicle above about 30 mph and no brakes applied (brake pedal/stop light switch is open). If the analog pressure does not rise when the PSM pump is engaged, then error 4460 is set. I believe this is the issue we encounter when changing to the 997 MC. The 997 does NOT have a separate PSM boost pump, which dramatically alters the braking circuit, particularly the need for a non-standard bypass circuit. The 996 cars have the Bosch 5.7 ABS unit, which is also found in BMW (ESC nomenclature), Audi and VW cars of the same period. There are minor differences, but all are generically Bosch 5.7. Check for yourself... You'll find BMW has two types of master cylinders, ESC and non-ESC. The master cylinder design is different. My hypothesis is this... 996 bypass is in the PSM boost pump -- not the master cylinder. Note that both are connected to the reservoir. The 997 cars have a different ABS system, which does not have a separate PSM boost pump. Therefore, they use standard master cylinder designs, with typical bypass circuits that allow fluid to flow back to the reservoir when brakes are not applied. Unfortunately, I couldn't find any PSM/ESC master cylinders with pistons larger than 25.4mm. So, we can't source a master cylinder from another vehicle that uses the Bosch 5.7 system. I think we're out of luck unless we build a custom MC. You might be able to do this by using the 997 piston/plunger assembly in a 996 housing that has been bored from 25.4mm to 27mm, but I'm not sure. We really need someone to disassemble the 2 units side by side to determine what makes them different and then go from there. Unfortunately, I tossed my old 997 MC when I reinstalled the 996 MC -- Kind of a "F*%$ this" moment. If someone has an old/extra 996 PSM MC and a 997 MC, I'm happy to disassemble them and compare the internals. The plunger/piston is easy to remove -- It is held in place by a snap ring. The only difficult part might be disassembling the two reservoir-to-piston channels -- There is a screen in there that might be press fit. John Look at the path from the charge pump to the master cylinder below... If the MC has a normal bypass, then no pressure can build when the brake is not applied. Also look at the front circuit bypass in the MC. Bosch 5.7 System Sensor schematic Max brake pressure reads 2.2V. Full scale deflection is 5.0V. Zero brake pressure in idle is 0.6V.

@ @jpurban , ..you did a very important study on this subject, I'm very impressed John ! Thanks a lot to share this very precious information with all of us. OK, from your reading, I understand and fully acknowledge that the pressure sensor is analog. So, the threshold level to trigger decision is set in the firmware code. This does help me to understand. If I catch it right, the 4460 error (in these cases) is not triggereing by a "braking" situation, but by a testing phase. I did effectively got a error when driving, kind of "cruising" mode, at about 25 to 30 mph (not using the brakes), where suddenly, the PSM and ABS lights turned on together. According to your study, it seems that the error is triggered by an "internal testing process", rather than a "normal" braking situation ! With a Durametric, we can manually start (and stop, as, it should NOT be running too long !) the PSM pump (this as well as the ABS pump). Would you think (I can try that one of these days), that ..doing so, would also trigger 4460 ? (This would be a clear proof that you are completely right with your findings !) If this is the case, one tricky way to turn around this problem would be to suppress this testing in the firmware, ..but I agree that suppressing such test, ..is may be not a very clever idea ! Still, this way could be less expensive ..than boring a standard OEM master cylinder and equip it with the piston of a PMN166 ! Need to think again ! Anyway, thanks a lot again, PS : We just lost your photos/diagrams ! (Images server down ?)

@GVA-SFO, Yup -- You get exactly the same error I do, under the same conditions. If we found some really capable firmware coder, we could eliminate the test, BUT the test is there for a reason. We fail it because changing the 997 MC defeats the PSM. If the PSM system can't build pressure when the brake is not applied, then it can't do its job. So, we're left with lots of less than ideal options... Ultimately, we really need a braking guru to help us figure out how to build/modify a MC that is PSM compatible with a larger 27mm piston. Hell, while they are at it, they could correct the 996TT excessive front brake bias! Are there any entrepreneurial brake experts out there? There is a market need... I bet you'd sell hundreds, if not thousands, of such a master cylinder. That might sound like hyperbole, but the potential market is huge... Think of the numbers of Bosch 5.7 cars (Porsche 996, BMW M3/M5, Audi S/RS) that would benefit -- I'll bet it is 100,000+ vehicles. Heck, the 996TT is 30,000 units alone. Breakeven/payback volume should be easy to achieve. John

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very very interesting ! in my case, i had this error, ..not with a turbo, ..but with a 986 (Boxster S). this is a 2001, with the psm pump on the passenger side. (note : i do have a big brake kit on the front, i.e.: large rotors with 6 piston calipers)

Hi guys, I have just finished this 27mm brake master cylinder mod on my 2002 C4 with PSM. The PSM/ABS error trips once the car passes 50kph/30mph with the 4460 code. Following suggestions found on the internet, I unplugged the PSM pump connector (by the pump itself), the PSM error lights up along with the error message when the car is started (the message reappears after about 30mins), but the ABS functions like normal. I've been thinking about this situation, would there be a way to tap into the sensor output wire to alter the voltage, so the ECU will see a correct voltage signal when it does the check? I know this wouldn't be the best way to do it as the ECU would then by fooled, but at least for those of us who don't track our cars, it can pass MOT without having to reinstall the stock MC and bleed the whole system. For those who have been having a hard time finding this master cylinder, if you check the part number 997-355-910-30 in the 997-1 parts catalog, you will find that the C4, C4S and Targa S share the same part number. I purchased the 997C4S item, which looks exactly the same as the 997GT3 one (with the two round milled out circles). The braking effect is the same as everyone has described, so I think the one I purchased is shared with the 997GT3.

Quotes source post: 15442463

Yes, I think this should be our mutual goal. Keep us up to date about your tentative of message to TRW !

Did some further research... I think I've found something that supports the hypothesis... We need a portless design...

What do you call a "portless" design ?

Quotes source post: 15497816

Portless designs relieve pressure through a check valve in the plunger rather than directly to the reservoir. This is a more complex design, which explains why the OEM MC is more expensive than the conventional 997 designs.

Quotes source posts: 15301814, 15301049

Hello Nickshu, I have tried to install the bigger MC in my C2 but no luck. May I ask whether your C2 have PSM or not? I'm wondering whether the PSM might affect the fault code. Thanks!

Hey Guys - Do you think installing a GT3 ABS unit along with the gt3 MC on a 996tt with PSM would eliminate the issue?

Saw this today for those still looking (no affiliation)- https://www.eeuroparts.com/Cart/CartList.php​​​​​​​

To those who might interested in this mod, here is the applicable models: 996.1 996.2 WITHOUT PSM (Error: 4460 code will be popped out after installation) 997/987

Seems like a lot of fun to try, but I wonder if the return on the time and effort expended is worth it for a DD or occasional HPDE car with the right upkeep, pads and fluid.

$238.90 from Autohaus AZ

Hi, I have a 2004 C2 40Jahre version with PSM fitted, and just got the PMN166 from mail order today. Will it fit without any errorcodes? Any idea/experience?

Quotes source post: 15633162

Unlikely it will work without any codes. As previous posts have stated, you will get ABS and PSM codes and error lights on your dash and both will be non-functional. These errors will come up as soon as you hit 50km/h (30mph), at which speed the ECU checks the pump for correct pressure. The PMN166 does not have the correct fluid routing for the PSM system, so the fluid pressure will not be correct, thus tripping the codes. If you unplug your PSM power plug, you will not get the ABS light on your dash, and ABS will function. The PSM light and error will remain. You might also feel your brakes to drag while driving, which is very dangerous. I have a 2002 C4 with PSM, and the PMN166/997GT3 brake master cylinder is not compatible with it. A friend of mine installed one in his C2 with PSM, it didn't work either.

Quotes source post: 15635299

Thanks, will give it a go anyways, as I got the MC and 12->10 adapters -> will send update as soon as possible. PS I got my MC from local parts store for roughly half the price (~130�) I've seen online and from web shops.

Quotes source post: 15638115

...sadly PSM error appeared. Right after the install and bleeding. Looking at the MC�s there are some differences there the sealing part to the booster and lenght of the connecting rod to the pedal... there is a 2-3mm difference there. Could that have some meaning in triggering the error. Anybody interested in the GT3 cylinder? Original going back to the car

So strange that so many of you have had problems with PSM errors. As said in my previous posts I installed this M/C in my 2003 C2 with PSM and had no issues. Drove it for a year with it, no problems. Drove several track days on Hoosier R7's, no issues. Mine would have been an from older LOT of TRW M/Cs. Wonder if something was changed internally on them? Seems doubtful. I no longer own my 2003 C2. I moved the 997 GT3 M/C over to my current 6-GT3 before selling the C2. My 6-GT3 does not have PSM however.

This was posted over on the GT3 forum: https://rennlist.com/forums/996-gt2-...r-psm-fix.html

For those that haven't considered used, I picked one up from car-part.com out of a wrecked 2007 GT3 for $100 with 30k miles on it.

Posting this for the benefit of anyone with a 996.1 3.4L C2 without PSM...this mod will not work. Ordered one of these for my 996 race car and as Priitpo has shown above the 997 GT3 MC mates up to the booster in a different fashion. I also have a 6 GT3 Cup master cylinder but unfortunately it also is not direct bolt-on either as the rear brake line port is M10 vs. the 2 x M12 ports and lines on the stock C2 ABS modulator unit. It does however use the same design as the C2 MC and bolts up to the booster just fine. I just put the stock MC back on for now. At some point I might tackle getting the 997 GT3 MC & booster installed but I believe that also requires the pedal actuator assembly to be replaced as well, which I haven't really researched yet. All is not lost as I will just put the 997 GT3 MC on my Cayman R which I had planned on doing anyway.

Quotes source post: 15778980

Others are reporting they had no issues?

worked perfectly fine on my 2000 non psm

For the record, my car is a 99 without PSM. I also used the TRW part, not the Porsche part, which I don't think should make a difference at all. The main issue was, as is readily visible in Priitpo's photos, the way the master cylinder mates to the booster is clearly a different design. As I alluded to in my original post, Pelican Parts makes reference in their guide to Brake Booster replacement for the 996 Carrera to the fact that Porsche cut in a new design and part # for both the booster and brake rod actuator for cars manufactured after Sep 13, 1999, so I suspect that that is at the root of the issue. If your car was manufactured after this date it will work, if before it won't. https://www.pelicanparts.com/techart...eplacement.htm

Quotes source post: 15779883

So the ebay adapter didn't work for you?

Quotes source post: 15779883

Very different statement than saying it won't work with any mk1 996 without PSM. I'm sure others will find this helpful.

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Yup, that's why I posted it here, figuring it out one step at a time and adding to the collective knowledge here on the board based on my direct experience.

Quotes source post: 15779971

Just to be clear, because I made my original post in a hurry, I've got five parts I'm working with here: the stock C2 MC and brake booster, the 6 Cup MC and booster, and the 7 GT3 MC. The 99 C2 MC and ABS modulator brake lines that plug into it are all M12 and theoretically wouldn't require an adapter to mount up as the 7 GT3 MC has two M12 sized receivers, so all good there. However, that point is moot for the reasons we all understand now above, ie. the booster interface design is different. The 6 Cup MC bolts up to the stock C2 booster just fine. It has 1 x M12 receiver at the front but it has 1 x M10 receiver at the rear which means it would need an adapter to make the M12 sized brake line from the ABS modulator work at the back. I ordered one of these off of Ebay, (ie. similar to the part used by Nickshu but in "reverse") but wasn't comfortable with it because the taper of the flange was slightly different, the hole is smaller, and it would have required me to bend the stock brake line more than I was comfortable with to make it fit. All of this could have been remedied with a little machining of course, but I'm rushing to finish the car up for a race at COTA and didn't have the time to mess with it unfortunately. After the event I will likely revisit this again and try to fill in a little more gray area that doesn't seem to be documented here. One of the things I need to verify is if the 6 Cup booster will work with the rod actuator on the car now. If it turns out it does, I will likely scavenge some stock Porsche parts and fab a custom brake line with an M10 sized adapter that can bolt right up the 6 Cup MC. If it doesn't work with the stock rod actuator, I will probably go through the trouble of swapping out all the components--the MC, booster, and rod actuator--to 997 GT3 parts and be done with it. Pictured is the 6 Cup MC attached to the stock C2 booster:

Damn that sucks, I was really looking forward to doing this mod. Has anyone with a pre Sep 13, 1999 996.1 attempted this and can confirm that the revised booster interface design won't work?

Quotes source post: 15780967

Hopefully I saved you some hassle. The easy way to verify this would be to look at the fittings on your current master cylinder. If you've got 2 x M12 fittings you know which one you've got...

$224.49 plus free shipping and a lifetime warranty https://www.fcpeuro.com/products/por...er-99735591030 I was considering doing this to my 1999 C2 (Jan '98 build) but since it may not be as plug and play as I expected, i'll just hold off. I dont track the car anyway. Planning a brake fluid flush soon and figured it would be the right time to do it. Oh well

This is still very strange to me. After changing the "break switch", I had about two months of driving, with no "4460 error", and suddenly, just got it again ! (In my case, I have a TRW master cylinder on a 986 (Boxster S), ..that have PSM. I really love BIG TIME the change in feeling of the brake offered by this mod (TRW large MC). should mention that my 986 has 350mm floating rotors in the front, with monobloc 6 cylinder caliper (Brembo Big brake kit). I'm not really ready to work back, but really hate to have this error. @ jpurban , did you got any news about the "portless" version, does it fix the problem ? If available, how do we order this MC ?

I looked everywhere for a master cylinder with a larger piston AND a design compatible with the Bosch 5.7 system also used on BMW and Audi. Unfortunately, the 25mm piston in our car from the factory is the largest available, as far as I could determine. So, we're stuck with the "soft" feel of the factory MC if you want your PSM to function. I bled the snot out of the factory MC and finally got it to an acceptable firmness after an hour of pressure bleeding + traditional pedal pumping. The pedal travels more than I prefer, but I can and will live with it. I'll bet that I ran a liter of brake fluid through the system to achieve the results I have. I miss the GT3 MC feel, but it is nice that I no longer get the ABS /PSM errors every 30 minutes.

Solution for the problem: https://rennlist.com/forums/996-turb...r-psm-fix.html

finally read this thread....i know what my next mod is when i do a brake flush....thanks Nickshu for sharing

I tried the solution offered by @Flewis763 Very simple and easy install of a JEGS adjustable proportional brake valve (63022) with some new lines from the 997 MC to the JEGS valve, and from the JEGS valve to the ABS pump. No ABS / PSM warnings and that nice stiff (very little travel) brake feel. This is on a 2001 Carrera 4 Thank you @Flewis763 great simple idea that allows us to use the 997 MC.

Hello, Great post! I am performing the swap as we speak. Does the reservoir simply just pop off? Thanks in advance! Franco

Quotes source post: 15908408

Yes. It pops into rubber grommets.

So here is my issue so far: 2002 C2 with PSM. 997 GT3 MC, High temp fluid bleed multiple times through whole system. One week into driving the car the PSM/ABS failure lights came on driving down the highway around 60MPH. Turned the car off and back on with no faults returning. Bleed the system again and put 1500 miles on the car with no issue. At the track yesterday and the car has performed flawless for 6 sessions ( 3 for my wife and I each). 4th session comes up for me and the ABS/PSM failure light comes on again down the back straight into turn 4 causing the right front tire to lock up. Does anyone know why the issue would be this intermittent? I am finding others are having the 4460 fault appear immediately or everytime the car exceeds 30MPH but this is not my experience. I just ordered the Jegs proportioning valve and will install that. 246GTSA, Which brake lines did you use to install that proportioning valve as the link shows OP made his own but it appears you used factory lines.

Hi @thurstonpowers3, I had the brake lines made up at a local hydraulic shop that specialises in making hydraulic fittings and brake lines. Took about 1 hour, they had my car and the valve to work with for placement etc. Total cost was about $40.00

Thank you! That is very helpful.

Quotes source post: 15929038

Any chance u have a colasped soft line or a caliper issue on the corner? U may have an additional issue since the mc has been good for a while.

The most likely culprit is probably the part you changed, the master cylinder, but there's also just the possibility that something else has gone bad, including the ABS/PSM hydraulic unit itself, all which you would want to eliminate to avoid frustration. Fault code 4460 -- Pressure sensor Possible cause of fault: - Short circuit to ground/voltage or open circuit in circuit to control module terminals 25, 26 and 42 - Plug connection on stop light switch faulty (aka brake light switch) - Adjustment of the stop light switch not OK - Wiring/ plug connection faulty - Pressure sensor faulty (replace hydraulic unit)

Quotes source post: 15931425

It has stainless lines and I just replaced the pads recently and the caliper seemed free but I will double check everything. Thank you for the input.

Good news is I've managed to figure out what was required to do the update conversion from the pre-Sept 13, 1999 master cylinder & brake pushrod design to the later one to allow the upgrade to the 997 GT3 MC. I went with the combination of the 997 GT3 mc and the 996 GT3 brake booster. In addition to the later design booster and pedal pushrod this also requires updating some parts at the firewall where the pushrod passes through. I'm just buttoning up the final details and will make a detailed post of what's required to get the job done including part numbers and tools needed later. One of the last things to do is make the final brake pedal height adjustment, so I have a quick question for those that have already installed the GT3 mc, especially for those that are tracking their cars: how much did your brake travel change under heavy braking? Did you find the resting pedal height too high and need to make adjustments to the pushrod length to compensate? With the bore size difference the pedal travel will be reduced of course and with all the new parts installed and not having adjusted anything the brake pedal is sitting about 28mm above the throttle. FWIW, Porsche specs 45+5mm, but that setting is likely assuming and compensating for the longer stroke of the smaller C2 mc bore. Any feedback or even better direct measurements like below from those that have this done already would be appreciated.

For the record, I've finished the conversion to the new brake booster, pushrod, and firewall seal parts that allows fitting the GT3 master cylinder to the early 996 and Boxsters and have created a new thread on it here: https://rennlist.com/forums/996-foru...l#post15967467

Quotes source post: 14894021

Just found a TRW 99735591030 on line AutoDoc for $95 in Italy... 106 euro with shipping. This should go well with the GT3 front and rear brakes calipers with 350mm discs all around I'm getting later in the month.

Due to the fact that I have a C4 it looks like I will have to install a rear brake proportional valve to keep the PCM working. Has anyone recently done this mod on a C4?

Quotes source post: 15929038

I just did this upgrade without seeing a thread about issues. I have a 2004 C2 with PSM (Which I keep off with the button). Mine is a dedicated track car. I flushed the fluid 2 times before going to the track this weekend after installing 997 GT3 Master Cylinder. First 2 sessions there was no issue. 3rd session on the outlap the PSM and ABS lights came on and pedal got real hard. Was applying brake with medium to high pressure at the end of straight and front wheels completely lock up destroying my tires. Did you do this jegs proportioning valve? Did it fix the issue on the track?

Quotes source post: 18120555

i had a similar issue but not until my third track day last year. The system checks the pressure at about 30mph and if it fails then the abs is disabled. I put this in after and never had to adjust it. Stays in the full open position.

Quotes source post: 18120587

Which brand/model is that one?

U should pull the psm plug for the track and fully disable it. The abs will still work but the psm wont be interfearing and our cars dont really need it in the track.

Quotes source post: 18120604

The only time I ever feel anything with it switched off on dash, is if I trail brake a little too long to its liking. Although, I would be all for it being completely removed from car. Which plug do I pull off? Will I have constant message about it on dash?

Quotes source post: 18120594

I believe it was the wildwood from summit racing.

The psm still interferes even with it switched off. Yes u will have a light. Ill see if zbomb can comment as he did it with his track car.

Quotes source post: 18120612

It�s the plug on PSM pump. The secondary circuit from the MC goes to it. also that�s the line where the valve goes.

Thanks all!

just for the record if you don't have PSM you won't need the adapters and you won't have any of these other issues correct?

All i know is on my car with no psm i used the factory 2000 c2 line from the mc to the abs block with no adaptor. I know Zbomb is doing this on his car with psm. It will remove the residual valve but he has the psm unpluged. I would assume the psm fault light would permanately be on, but im sure z will just disco the dash light. I do not know how else this will effect a street driven car.

Quotes source posts: 18120555, 18120604, 18120612, 18120622

That sounds an awful lot like you encountered ICE mode, that's an ABS issue, not a PSM one. Yes, the PSM for me was slowing me down and wearing the rear brakes for no good reason. As was said, you just have to pull the plug at the pump, I have posted pictures a couple times before. You can pull this plug and NOT get an ABS light, which is the one you should care about. Can confirm, with the PSM switched off it does still interfere, although with less aggression. If you look at some of my videos where you see brake activation while at WOT, that is the PSM intervention and the only way to disable it was to electrically disable the pump.

So maybe this is a dumb question, and if it is, forgive me. I'm getting ready to do brake lines and the GT3 MC on my 03 C2 w/o PSM. It sounds like I shouldn't have issues with lights etc., but my concern is the bleeding process. Will I be able to bleed the brakes with my pressure bleeder like normal after this, or will I have to track down someone with PIWIS or Durametric to enter some kind of bleed mode for the ABS pump, etc?

Undo the lines at the MC and plug them to make sure the ABS hydraulic unit doesn't lose the brake fluid inside it, then standard bleeding will work (as in no necessity to switch any valves inside the ABS or run the ABS pump to bleed the system).

I didnt have an issue with just the pressure bleeder.

If you enlarge the master piston diameter, the pressure is reduced and causes you to have to push harder for the same friction right? Why would you do this? And sure the pedal would travel less and have a solid feel

Quotes source post: 18582729

1. A firmer pedal is more confidence inspiring at the height of braking demand (for me) 2. A firmer pedal that may degrade some over hard use provides better feedback of the drop off that is occurring (for me) 3. A firmer pedal allows a finer degree of modulation under hard use when inputs are generally stronger (for me) Going to the GT3 master is right up there with the best modifications I have made for track use.

Also in my case (and zbomb) we have updated our calipers and require more volume. The gt3 mc makes the pedal feal much better by being firmer.

Quotes source post: 18583279

what calipers do you use? more piston area?

Mine have more pistons. About the same area. 997.2 GT3. The GT3 master works fantastic on the stock brakes though.

Im using all 4 gt3 uprights and front caliper gt3 6 pots. In the rear im using c2 front calipers instead of the gt3 caliper (more piston area). Zbomb is using 997gt3 calipers with adaptors. If u do the math for the front and back bias the set ups r the same ratio but my pistons r larger (front and rear) so i get 30% more force.

In case anyone still follows this, the difference is additional flow restriction in the flow path to the reservoir in the plunger in the PSM MC. The flow restriction has some spring and needle valve in it and it restricts flow significantly compared to the GT3 (I can blow in each.) For info i destructively removed the valve. See below, GT3 on top. No way to swap parts, they are all punched and pressed on. This is why the Flewis solution works, but it has the downside of restricting flow going out of the MC to the front brakes also.

Quotes source post: 19523178

How is putting a proportioning valve on the secondary circuit restricting flow going to the front brakes? My proportioning valve is set to full flow. Edit: Maybe I am wrong but I thought with PSM the secondary circuit is being used for that. And that it was applied to all four wheels.

Quotes source post: 19523356

The pre-charge pumps into the Front brake circuit. Putting a proportioning valve on the line between it and the MC, even with the valve fully in, still lowers pressure at 1200psi, which is the purpose of a proportioning valve. See graph below from Wilwood. If your valve is fully out, you are severely restricting pressure to front brakes. https://shop.wilwood.com/blogs/news/...ing-valve-work

Thanks, I believe I had seen this when I put it in about 100 track days ago. I guess I should get around to installing that brake pressure sensor and see what I'm generating. Stock 996 is really a momentum car now so I would be surprised if it's that high under normal laps. So the rear brakes are not engaged by the PSM?

Quotes source post: 19523493

PSM operates all four brakes via the Bosch 5.7 ABS unit. The pre-charge pump pressurizes to ~300psi the a) front brake circuit of the MC and because the MC is tandem, the rear circuit also, and the front brake port of the ABS unit. (see graphic below). The precharge pump does this so that PSM can work without any braking from the mush bag in the front seat and still have an effect. From a BMW MC, but works the same as 996.

Amazes me when parts are seen as an upgrade the vendors triple the prices for these parts. What use to be $175 is now $350 to $500 now

They must be avid Rennlist readers...

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TRW PMN166 is currently available from several retailers for $200 to $250, same price as six years ago.

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Yeah you may want to check the facts. I purchased from FCP 2020 $197.00 Current FCP price $247.00

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Facts checked

Will this work on a 2002 C4S?

https://www.fcpeuro.com/products/por...er-99735591030 GT3 MC is now $85

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Thanks!! I�m in!!

I called TRW supplier in Australia when these were on sale November last year and they told me that TRW won't be making them anymore. So grab them while you can

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It does seem that manufacturing has shifted to China. The one I bought in 2020 was made in poland. Also if you search by porsche part number a lot of them pop up on ebay for as little as $52. I would feel confident buying from FCP as it's easy to return. If anyone does get one post a pic of what you get.

Quotes source post: 14795023

THE ADAPTER-- Why couldn't you just drill out the the M12 on M/C and use a Time Cert 10mm fitting in it? It can be sealed easily and Time Certs have the proper size tap, roll-tap, and fitting. Would this be a more simple solution? Curious. YMMV

Its a bubble flare seal. U cant just rethread. U can get the correct line from porsche its from an early nonpsm 996 or boxter.

Current setup is with 2 M12 nuts on the master cylinder. However I have the brake booster as part #996 355 025 03. Anyone know if the 997 GT3 MC is a direct fit or would require a brake booster from a 996.2? Thanks!

It bolted right up to my 2000 c2 non psm booster if that helps?

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Eyeing it up from the pics, it should bolt up to this brake booster posted but wasn't sure if I was missing something. Thanks!

Quotes source post: 20517682

I�m in the same boat with an early car. I�m 98% sure that is the same number as mine, and considered a �won�t fit�. I haven�t tracked down why it won�t fit� there is discussion further up this thread but they don�t say if the MC diameter to too large for the booster, or if the bolt pattern is off� perhaps the engagement depth is further? It seems to be close. The added frustration is the booster change affects parts on the other side of the booster too. I ordered up a few of these bits, but if I can make the old booster and new master work together I will. But� congratulations! Early car confirmed

Quotes source post: 20517853

Haha thanks! Love the early cars - cheers on that!. Ahh ok, so we would be in the same boat then and why I posted my question. Once the MC arrives, I will just do a visual check but it sounded like, from a related thread, that we would need the grommets, new booster and the connecting rod to make it work... shame. The boosters are pretty expensive so I may just return the MC if that is the case.

I think it�s worth taking a look to compare. The reason I think it SHOULD work, is that reading through the Porsche Boxster bulletin for the updated booster, it lists all items to upgrade - including the firewall grommet and push bar - but it�s doesn�t say anything about needing a new master cylinder, only remove and reinstall. I read that as though the old MC could be used with the new booster. It appears two users (@nickshu and @cog-zoom) in this thread mention the mounting scheme is different, but not how or what the issue may be. A new brake booster for a high mile/nearly 30 year old car sounds like a good idea too, but at $700 or more replacing a clean and working unit is not my top priority! If it was $100-$200 I could call it maintenance.

There is always Specialized German for used parts and a few other out thre on ebay. Its not a high failure rate item so used should be more then fine

I have been fighting some strange PSM/ABS issues with my 996 and the only thing I can think of that might be causing it were these two things 1) 997 GT3 Master 2) DS3.12 pads To avoid slamming a wall or jumping a curb, I decided to put the standard master back in and go to some less aggressive pads. I know that there is a "trick" to put a proportioning valve on the rear side of the master lines but I'll be honest, sometimes it's not worth it especially when you're screwing with ABS. I watched a C5 Z06 in front of me hit the inside wall on the back straight of VIR several weeks ago at 135mph because of an ABS issue. I will be curious to see how it handles now. The strange thing is, I have used the 997 GT3 master on numerous other cars with no issues. It is important to note that none of the other cars I've installed them on have PSM, and that my car struggling was a C4 which has the PSM pump. I am not ruling out the master as the issue, but it certainly pissed off the ABS and/or PSM more than the standard unit. --Aaron

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My experience. Installed MC Spring of 21 in 2001 C2 with PSM Did two track days with no issues. Third track day (10th ever) ABS PSM lights came on on track. Reset car in the pits, goes away only to come back on at about 30mph. No ABS. Installed proportioning valve but is left full open. 100 track days later never came on again. It has to do with a pressure check it does at around 30 mph, fails and throws the lights.

I�ve referred to this thread frequently over the years divining if this is a good project for me. I keep coming up with �no�. This brake plumbing was designed in the 90�s. The 996 system will never feel like the modern systems employed this century. That said, the stock brakes are ridiculous good. I get the desire for better brake application feel, but I think there are some less impactful ways to improve it. The whole idea is to brake later and smoother, yes? Pads, fluid, lines, technique, practice are easier to change than the whole MC set up. Flat spotting, warning lights, bad brake behavior at the most inopportune time are not good outcomes. The 996 pedal box and pedal distances cause me enough trouble, with my big feet, for heel-toe while max braking. For me the modulation issue comes as I release pressure. But that�s all just timing the trail brake. If I�m a little abrupt I�ll call it �trail brake rotation� like I meant to slide the rear and fix it next lap. Sure, less pedal travel would be nice. I�ll disco the PSM connector while at the track and be happy with the usual so-so brake pedal travel. I�m actually considering the auto blip so I can concentrate on the brake pedal and do better threshold braking and not over slowing. Looking at the cost, wiring instructions and the gymnastics required for the Auto-Blip, seems a reasonable experiment.

Yeah it�s too bad PSM gets upset about it. Using a bias valve to show the pump it can make pressure is a good solution really. The improvement in modulation with this mod is the increase in pedal pressure, as much (if not more so) than the shorter pedal travel. Yes they are obviously the inverse of the same changing leverage relationship. Most OE systems are soft and long. It�s really hard to modulate pedal position. Feeling position is called proprioception� not something people are generally very good at with our feet, especially at +1g looking through a corner. As a result, with a soft pedal, there may be more of a brake/perceive effect feedback loop. Race cars have hard pedals. It�s easy to �feel� force, so it�s easier and more intuitive to modulate predictively based on what you want the car to do. That is the improvement in control this modification is making. Outside of PSM and the design pedal force for general use, the risk this mod increases is brake capability during a brake booster failure. You will need more force to produce the same brake output, and without help that could be difficult. This may be mitigated by the pad friction material you are using, or any larger brake discs (Girodisc setup) will give you some advantage back. Those might make this change more diserable too. I suppose if you don�t mind the pedal travel and want a firmer pedal, you could try to adjust the amount of vacuum in the booster with a vacuum regulator. I�ve thought about that on other cars, but ended up deleting the booster!

Its a very worthwhile upgrade is you dont have PSM. Hoping you guys can figure out how to make it work with PSM.

I really love the brake pedal feel with the 997 GT3 Master, I did not like jumping the giant curb at t16a when the ABS decides to spazz out when I'm fresh off the rev limiter in 3rd. First time was a broken oil pan, second time was a small crack in the front bumper. I'm just glad I didn't get to test out all of the wonderful new walls VIR has decided to add. --Aaron

Im not sure thats the mc. The abs in general sucks for the track. It goes into ice mode whay too easy when on a 200tw tire or better. If u think its a psm thing u should just unplug it from the abs when on the track. U deff dont need the tc in a 996. I have to greatly change my braking profile when i swich from a nt-01 and scrubs so the abs doesnt freak out. Im my case i need the larger mc as im using gt3 front calipers and the rears r c2 fronts. Its a lot more piston so i need to move more fluid. This is from another thread but its a good explaination of ice mode in our cars. Google says.... Key Aspects of ABS Ice Mode: Feel: The brake pedal becomes extremely hard and "buzzes" or pulses, yet the car fails to slow down significantly. How to Exit: To immediately exit ice mode, drivers must completely release the brake pedal to allow the ABS to reset, then reapply pressure gently. Prevention: Avoid abrupt, "stomp" braking on surfaces known to cause it. Progressive braking allows the system to accurately detect the available traction. Context: It is largely considered a fault of road-car ABS systems designed to prioritize stability over performance. Motorsport ABS systems do not have this issue. Cause: The ABS module detects a sudden, extreme deceleration rate (often from bumps, high-grip tires, or rapid braking) and misinterprets this as a low-grip surface like ice.

I can get ice mode really easily, as AI said hard braking over bumps is the trigger. Hard fast brake application is another trigger - you know, the brake technique taught at race schools. I found a slightly slower attack on the brake mostly prevents it. Ironically the 997 master is easier to get that hard fast brake application. I did not run into ice mode with the 996 master because of the longer travel. And please unplug the psm pump. The 996 psm is good in novice run groups, it's dangerous in higher groups.

Have never experienced ice mode in mine.

With my old C4 (standard master) I would consistently get ice mode in corners that fell off and had a rough surface. Every lap at Barber T11 is a good example. I have thought about going to the Teves MK60 standalone ABS unit using a Happy Cactus converter so I don't have to run new ABS sensor lines. The Teves kit is what a lot of the Spec Cayman guys are using and I have done an install myself. If I get around to it I might try this in my 996, I'm on the fence about hacking up the wiring though since I still consider my car a street car. I thought about the cup ABS unit, but you loose the speedo output which I do not want to deal with, and its pricey. Guess I just need to go 996 cup shopping! --Aaron

With or without the GT3 master cylinder I havent gotten ice mode. But I dont have PSM. Dont know if the Brembo GT big brake kit and Guard LSD i am running have any positive influence over it. I have run Sport Cups, Proxies, RE71RS and Hoosiers with the set-up and no issues over the past 22 years on the track.

Mk1 cars with their non-cambus abs r a lot less sensitive to tire size and and ice mode then the mk2 systems.

Some of it may also be brake application. An initial light application followed by smooth but hard braking may help. I have always run 225x40x18 and 285x30x18 tires on my MK2. Havent tried bigger wheels nor bigger tires which may have something to do with it. Dunno.

I'm running within a few % of the original tire size- 245/40 and 295/35 RES71RS. Will give it a shot here soon with the stock master and report back. Wish there was a better way to test it! --Aaron

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I run 275/35 18 on street and at the track. Zero issues with a stock master cylinder in rain or dry. I have gotten ice mode on street when it�s expected�like bouncing over pavement in wet and then jamming on the brakes.