GT3 master cylinder ugprade for early 996s & Boxsters

Finally managed to sort this out. Net/net is you can convert your master cylinder to the GT3 part if you have a 996 or Boxster made before Sept. 13, 1999 but it will require simultaneous conversion to the updated brake booster, brake pushrod mechanism, and firewall seal parts. Documenting here for the benefit of others' future reference. Parts needed: Your choice of one of these brake boosters with the updated design: 2003 996 C2 Brake Booster (TRW or Porsche Genuine options): 996-355-923-00 or 2004 996 GT3 Brake Booster (Porsche Genuine only): 996-355-923-90 And one each of these: 997 GT3 master cylinder (TRW or Porsche Genuine options): 997-355-910-30 Firewall seal update set: 000 043 204 66 Updated brake push rod: 996 423 165 05 Threaded bushing: 996 423 307 00 Pin: 996 423 308 00 Tools needed: 1/4� ratchet with extension 3/8� ratchet with extension 1/2� ratchet Torque wrenches covering values 7.5 ft/lb, 17 ft/lb, and 36 ft/lb T45 Torx bit (for the long brake booster bolts) H5 Hex bit (for intermediate piece positioning bolt) 10mm �mini� combo wrench (for the small nut that holds the two pushrods together) 16mm combo wrench (you will need two 16mm wrenches for the brake pedal to pushrod bushing and pin removal) 17mm combo wrench 19mm combo wrench 6mm 1/4� socket (or flathead screwdriver to tighten the bellows clamp) 13mm 1/4� socket 16mm 3/8� socket 22mm 1/2� socket 11mm flarenut wrench for hydraulic unit brake line connections 13mm flarenut wrench for master cylinder brake line connections Vernier calipers Small carpenter square (or vernier calipers & straightedge) to verify brake pedal height to throttle measurement Rubber lubricant or tire mounting paste. I used Super Lube Silicone Lubricating Grease that I had laying around. Tips/potential hangups: Save yourself the wasted time and frustration and just remove the ABS hydraulic unit. You will not get the old booster out with it in place. Also, if you have PSM which I didn�t, you will need to remove the PSM booster pump as well. Same goes for the intermediate piece (#11 on the parts diagram). You will need it fully out of the way to get the new firewall seal pieces in place. The most tedious/difficult part of the job for you will likely be setting the updated firewall seal pieces (7.2 & 7.1) in place. Make sure the sealing ring (7.2) is set evenly and fully into the cutout in the firewall. Pushing the connecting piece (7.1) into the sealing ring is the hardest part. Get the intermediate piece completely removed and out of the way, lubricate the two pieces and use all of your body weight and leverage from the front of the car to push it in. I needed a lot of leverage, a good double handed push and all of my 214 lbs. to get this seated. Unless you have World�s Strongest Man levels of strength, you�re not going to push it in with one hand from the side of the car. Make sure you note the torque value for the bushing and pin that hold the brake pedal and pushrod together. While unlikely given the design, having it snap and fall out from being over torqued when you stand on the brakes with all your weight to panic stop on the street or at Turn 1 at COTA would mean a very bad day� The indicated value is 7.5 lb/ft. Go for a test drive in a controlled environment afterward to make sure everything is functioning correctly. Then come back in, pop the hood, and check for any leaks at any of the hydraulic line connections, bolt/nut torques, etc. I actually did not set the brake pedal height per the spec in the instructions and left the adjustment of the inner pushrod on the master cylinder where it was given that the new mc requires less pedal stroke. I may adjust this in the future based on track testing and will report back about that after the car has been tested in a controlled environment at high brake pressures. Everything else is per the attached instructions. In total, I�d rate this 3.5 out of 5 wrenches on the Pelican scale. This is a pretty messy job with the inevitable brake fluid mess and requires a fair bit of disassembly/reassembly, so if you�re unsure you should leave it to a pro. Given you�re messing with the heart of the braking system, which I�m always extra cautious about working on anyway, remember doing it wrong could result in serious injury (or worse) to you or someone else if you get it wrong. Silly I have to say this, but I'm obviously not responsible or liable for either and I'm posting this for educational purposes only. Feel free to ask any questions here or DM me and I'll be glad to help! Nearly disassembled but ABS hydraulic unit and intermediate piece still need to be fully removed. New firewall seal and updated brake pushrod being fitted. Verifying clearances and test fitting before completing reinstallation. Fully reinstalled and brake fluid topped up ready to bleed. Updated firewall seal and bellows fitted.

Thanks for the update! As far as I understand, an updated brake booster and push rod is not required to use the 997 GT3 MC. Were you having issues with just the 997 GT3 MC?

It depends on when your car was made. Porsche did a mid-model year cutover in Sept of 1999 to an updated booster, pushrod, and firewall seal design. If your car has the older parts the GT3 MC is not a direct bolt on and you will need to update the others in order to make it work.

This needs to be a sticky. I have a March 1998 build and this is a mod I will likely do in the future.

Bumping this thread. Find it timely. My car was built on 3/19/1999. I am going to do the upgrade. Looks like I will have to get the extra parts. Bummer.

Glad you found it useful.

Are there differences between these brake boosters? one is better than another? Regular C2 one is readily available and much cheaper. 2003 996 C2 Brake Booster (TRW or Porsche Genuine options): 996-355-923-00 or 2004 996 GT3 Brake Booster (Porsche Genuine only): 996-355-923-90 This one from the bay seems to include all the parts needed. https://www.ebay.com/itm/TRW-Brake-B...cAAOSwuSZe1-~t

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I've got the same questions. What are the advantages to this upgrade? Thx!

I didn't have to do **** on my 99 boxster. bolted the 997 gt3 MC right in. Better pedal feel for sure.

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Does your car have the last 6 digit Vin numbers before 620337 or after?

great write up . Thanks for this

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627xxx

Bringing this back from the grave... I see that some of you with late build 99's have been able to do this as a bolt on. My 99 is newer than the cuttoff vin. For those who've done it - is it literally just unbolting the old MC and dropping in the new 997 MC? No new newer 996/996 booster required? This is on my spec boxster. 997 Thanks!

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Anyone care to chime in on this question? Is this all for improved pedal feel and ostensibly better stopping power?

Better feel, and I believe more rear bias

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In my case, it was a simple uninstall and install the new 997 GT3 MC.

I realize this is the 996 forum and there are no 1997/1998 996's but since the OP referenced 986 Boxsters and this thread was helpful for this swap (legal for Spec Boxster racing class) I am replying here. I did this installation today on my Spec Boxster race car which is a 1997 chassis. Some important notes on the install I came across. 1997 cars have a different pedal cluster than 1998 and 1999 cars. If you look at the Porsche parts manual you will see that there is a separate diagram page for the 1997 pedal cluster vs the 1998-1999 pedal cluster. The brake pedal on the 1997 is different such that the updated bolt-type pin on the updated brake push rod will not fit. Additionally the brake and clutch pedal shaft and bushings are all different on the 1998-1999 cars so swapping out the pedal for a later version on a 1997 may not be a direct swap. Given that the pedal mountings are a welded part of the body, and the pedal shaft is shared w/ the clutch and has several different parts of different design...not to mention it's all in an area that is very difficult to access, especially in my car w/ a full cage...I chose not to risk buying a bunch of parts to try to swap the brake pedal to the 98-99 style, and risk finding that it would not work. So I figured out how to modify the 1997 push rod to work with the updated/later design...as it turns out they are not that different. Looking at the two pedal push rods, the 1997 version and the later/updated version the difference is the 1997 version uses a smaller hole at the brake pedal end with a pin and clip instead of a bolt. It has a spring centering piece also that the later/updated version does not have. Other than this and the "fins" on the forward end for holding the old style rubber boot, the 1997 version and the Updated version are identical in pretty much all dimensions. To avoid too much brain damage I ground off the "fins" with my angle grinder and did the installation using an OEM Porsche GT3 brake booster and the new style boot and connecting piece which all bolted up perfectly. The later style "connecting piece" that bolts the brake booster to the pushrod (eliminating the earlier clip style connection) fits perfectly w/ the original 1997 pushrod. You could probably skip grinding off the "fins" but if the angle is not perfectly straight on the push rod it appears that it could catch on the edge of the newer style plastic boot retainer that goes through to the passenger compartment, this could prevent the brake pedal from returning back to rest position. It's also worth mentioning the "connecting piece" and locknut comes already installed on the new brake booster and is set at 138mm as recommended by the Porsche TSB. I would recommend measuring to be sure it was set correctly at the factory but mine was set spot on. Needless to say modifying a brake part is something you should do at your own risk, so while I am sharing the knowledge here I cannot take any responsibility for others who may chose to try this solution, do this at your own risk. A couple of other notes on parts: Firewall seal update set: 000 043 204 66 - Several parts in here are duplicate as they come together already installed on the new brake booster, however it appears you cannot buy them individually so just get this kit and be aware there will be duplicate parts. Updated brake push rod: 996 423 165 05 - Not needed if you have a 1997 car as you will have to modify the existing pushrod as noted above. Should fit 1998/1999 cars as they went to the later style brake pedal for 1998 (indicated in the Porsche parts catalog) Threaded bushing: 996 423 307 00 - Not needed for a 1997 car unless you replace the brake/clutch pedal cluster (Which may or may not be possible). Pin: 996 423 308 00 - Not needed for a 1997 car unless you update the brake/clutch pedal cluster (Which may or may not be possible). Here are some photos.

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What year 996 do you have?

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I have a '99 with a build date of August Augucable throttle) I believe. I can confirm when I get it back from the shop.

It seems that this brake booster is now $600+ and the TRW part is no longer available. This week I am finding it cheaper, but, if we use a 997 part such as 997 355 025 36, would that work? I am just wondering if we could source a used part instead for cheaper. If that�s not advisable, let me know.

The 997 gt3 master cly is now being made in china and no longer by trw. Fcp has it for aroind $80 now

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The one I had listed from FCP was made by TRW, but the country was listed as China as manufacturing. It was $85 Now it is $310 Still, TRW, still China

The TRW PMN166 MC that�s the �997 GT3 MC� is also the MC for any cars with PCCBs, so GTSs, Turbos, etc. They aren�t about to go NLA. The prices seem a little volatile but I found one for less than $100 shipped last week. TRW China, manufacture date was 2022 or 2024, can�t recall.