Problem w/ GT3 Master Cylinder Install

Installed the TRW GT3 master cylinder on my 2011 Cayman S today, and I've somehow made the excessive brake pedal travel (or "mushy" brake feel) worse. I suspect this is a result of a less than optimal bench bleed of the new master cylinder but can't be sure. The new MC didn't come with a bench bleed kit, so I improvised by holding the MC in a vise with the reservoir attached to the top of the MC while a friend kept the holes that connect to the brake lines plugged while I slowly pushed the piston in and out. Another potential issue during the install was my inability to attach the new MC into the brake booster with the reservoir still attached because the reservoir was in the way. As a result, I removed the reservoir, attached the new MC and then reinstalled the reservoir. After getting everything reassembled. I filled the reservoir, and bled the system twice (via the calipers) using a Motive Power Bleeder. So far, I've seen no improvement in brake firmness... In fact, it feels softer now. The only other thing I can think of that's causing this (besides possibility of an incomplete bench bleed) is that I have the wrong part. I ordered the part from ECS tuning and the part number on the box does match the part number listed in other threads on this site. I'm sure that possibility is a long shot but really can't think of any other reason why this is happening. Did I miss a step? I'm thinking my only two options at this point are to remove the MC, bench bleed (with a kit this time), and bleed the system again. Or, hand it over to one of the pros at my local independent shop and have them do the same thing but also flush the ABS (which I am unable to do). Any thoughts or suggestions are greatly appreciated.

I had a shop install my GT3 MC in my '06 CS. The labor bill was considerable in that they had to very comprehensively flush the system; not just bleed it. It is a very time consuming process, that is necessary to make sure the ECU and ABS are very happy. I swapped out a PCCB MC for the GT3 unit and am very happy with the results. Good luck!

Do you have a manual transmission? Apparently you need to bleed the clutch mc as well when you do this swap. My shop spent about 4 hours on install, flush and bleed. Pedal is rock hard and high. Quite a change. Good luck!

Saildoc. Thanks... Yes, I have a manual trans. Didn't know about the clutch mc bleed... How does that affect the brake pedal? Not doubting what you're saying, just a novice trying to learn more. I really hope that this can be solved with a full flush and that I didn't get the wrong part in the right box...

did you use the durametric to cycle the ABS?

Thanks for the response. No, I don't own a Durametric. I've read about how others have done this but wasn't sure this was a necessity. The install articles I've read don't mention it. Unless someone has a different suggestion that I can DIY, I'll probably take to my local independent shop for a full flush to include cycling the ABS. Will a full flush fix the MC if it has air in it from the bench bleed or is that only solved by removing and doing another bench bleed?

A prior poster reported a similar issue after his shop installed a TRW GT3 MC. It turned out that although the box was properly labeled, the MC in the box was a standard MC, not the GT3 part. Swapping to a known GT3 MC cured the problem. While I hope your issue is simpler, don't ignore that possibility. That post was one reason I bought the Porsche part from my dealer and had them install it. Total cost for parts & labor (2 hours) was $600 as a reference point.

Thanks. Any idea how I can tell I have the right part? When I received the part, I looked at the numbers on the actual part compared to the box, but nothing matched. If it is a case of the wrong part, I don't know how I go about proving this to the company I bought it from.

ClaymoreSix, Assuming you have the right part I think you still have air in the system. You might try using the pedal to bleed the brakes with the pressure bleeder attached starting with the right rear caliper. I was able to get all the air out when I did the GT3 MC install without needing the Durametric. The clutch shares the brake MC fluid. It is a good idea to bleed the clutch while you are at it since they share the fluid. Good Luck, Rob VN

Rob, Please don't take me wrong, but I whenever I thought about using the pedal 'with help from the bleeder' I always backed up (aka chickening out...) Question: By pushing the pedal with the pressure bleeder connected don't you have the risk of damaging the seal lips on the plunger by trying to overcome the pressure from the bleeder? But you are saying that you are doing it and never have an issue? On my other cars (Alfa & Fiat X1/9) I usually set the bleeder @ 10psi but the Porsche manual tells you (if I remember correctly) @ something like 20-25psi... and... you are supposed to leave the clutch bleeder open for 15 or 20 seconds, that calls for two fluid bottles.. lol .

Gilles, The extra pressure developed by the pedal helps purge any hidden air bubbles. There is a Porsche workshop instruction that describes this method. It is posted somewhere. That was good enough for me! For the clutch I just opened it enough to get bubble free fluid out of the clutch and cycled the clutch pedal by hand. Rob VN

He is correct. The manual says to use the pressure bleeder and the clutch pedal for the procedure. If it is still soft, then you have to cycle the ABS according to the instructions. That is why the dealer charges so much. I bought a Durametric Pro and did the procedure and it worked perfectly. Good luck

Another question: when depressing the brake pedal to bleed the system, about how many times should I do this and should it be done very slowly or very quickly and firmly? The power bleeder will be attached. Thanks.

Just approach it the same way you would normally do, using the 2-person method. The only difference is the external pressure applied by the power bleeder. So, for LH drive cars: Remove cap from MC reservoir Extract old brake fluid from MC reservoir (as applicable) Fill MC reservoir with fresh brake fluid Attach power bleeder to MC reservoir, and pressurize to the specified value Bleed RR brake caliper as follows: Attach hose from catch bottle to outboard caliper bleeder screw Have assistant pump brake pedal 3-4 times, then hold it down until you tell him to pump it again Open bleeder screw until brake pedal goes to the floor, and brake fluid stops flowing Close bleeder screw Repeat steps 6-8 until fluid runs clear, with no visible air bubbles Repeat steps 5-9 for inboard caliper bleeder screw Release pressure from the power bleeder Top off MC reservoir with fresh brake fluid Attach power bleeder to MC reservoir, and pressurize to the specified value Bleed the LR, RF, and LF brake calipers (in this order) using the same steps outlined for the RR brake caliper. Don't forget to top off the MC reservoir between bleeding each caliper, or you'll risk introducing more air into the system! Release pressure from the power bleeder Top off MC reservoir to the "full" mark with fresh brake fluid Install cap on MC reservoir Dispose of used brake fluid according to local recycling policy, laws, ordinances, etc. NOTE: Assuming the MC is installed on the driver's side, bleed brake calipers on RH drive cars in the following order: LR, RR, LF, RF.

My GT3 front brakes suck too, so this is helpful. FWIW FarnbacherLoles installed the GT3 MC in my car and the part no. is 997 355 910 10. It cost $454.21 in 2008.

Problem solved, and it didn't cost me anything more than a couple of hours and 2 liters of brake fluid! I bled the system again, but I did a couple of things differently this time. First, I found a safe place to activate my ABS a couple of times. Afterwards, the pedal felt slightly more firm but still no better than the stock MC. Next , I bled the system using the power bleeder AND depressing the brake pedal simultaneously. Finally, I made sure not to open the bleed nipples on the calipers too far as I was advised this can let air back in. I went through 2 liters of fluid which may have been overkill but I finally got the result I was hoping for in the first place. The pedal is way more firm now. As other posts have stated, it will never feel like a GT3 (or even a 997 S, as I've tested) but it is a vast improvement over stock IMO. Thanks to all who offered suggestions! Now, I'm ready for my next track day!

I found that if you bleed both sides of each caliper it helps.

So question for all the people who are familiar with the ABS system in the Cayman . While I was going through school to become an automotive technician (changed plans and am now going for a mechanical engineering degree) I learned that electronic ABS systems can be purged by pumping the pedal AT LEAST 25 times. This opens up the valves on the ABS reservoir and allows all the old fluid to be purged. Just curious if anyone knows if that applies to the Cayman as well.

Did you mean to say bleed both sides of each caliper simultaneously ? Otherwise, the procedure I posted has this scenario covered. I deliberately specified bleeding the outboard screw first, then the inboard, to follow the "farthest-to-nearest position from the MC" sequence to its logical conclusion. PS I'm glad the OP had a successful outcome!

I installed a GT-3 master cylinder today (TVR version, not OEM), along with braided stainless steel brake lines. The install was completely trouble free, thanks to the insight I received from the posts in this thread. Many thanks to all! I bench-bled the master first. After I got it installed I did a power bleed of the system using a Motive power bleeder. Then, to be sure I got out all the air, I did a second bleed manually (pumping the pedal), but with the Motive attached. End result - a seriously firm pedal, light years better than before.

FWIW the part no. I gave in post #17 for the GT3 MC was incorrect. I found out that FL installed the PCCB MC and that is what that part no. is. I have since replaced my MC w/ a new PCCB at the recommendation of Spencer Cox who was formerly at FL when my car was built. He said it matched my calipers/rotors ( GT3 front, CS rear) better than the GT3 would. So far not thrilled w/ the result. I too think I need a better bleed.

The master I installed this week is the TRW version of the GT3 , which I bought through ECS Tuning. They've got both versions (TRW and OEM). Only difference is price - the OEM costs $150.00 more. Here's a link: Home Page > ES#2539327 Brake Master Cylinder - 99735591030 During a full day of hard braking on the track yesterday at PBIR, the pedal remained completely firm. No fade, no spongy feel. Completely happy with the results.

One other note on the install process. The TRW master does not come with a bench bleed kit. To bench bleed it you will need two barb fittings to connect the tubing between the outbound ports and the reservoir. After striking out at local auto parts stores, I used a $21.00 bench bleed kit that I found online with barb fittings of all sizes: Texton 804 US/Metric Bench Bleed Kit http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=231018613981

Just installed my GT3 MC and SS brake lines over the weekend. Had the new parts on in about 2 hours and bled the system twice, using the durametric to cycle the ABS pump. Pedal firmness is nearly identical to my Dads 7.2 GT3 ...just wish it had his calipers Plan to drive it a few hundred miles and bleed the system again for good measure. Should have done this mod a long time ago!!

I plan on doing my install tomorrow. I purchased two .5 liter bottles of Motul RBF600 but am worried that wont be enough to complete the install. Any recommendations on this?

It should be more than enough. I did a complete fluid change from stock to Motul last year and used just over one 0.5 litre bottle.

Actually, no. Full flush will require about 1 L (slightly less). I know because I've done it using dyes to know when is enough. For GT3 MC install, I'd recommend a lot more than 1 L since you'll need to either bench bleed the MC or keep flushing++ +/- pressing brake pedal during flush until you get all the air bubbles out of the system. They can be stubborn.

Successfully installed GT3 MC today. Pedal firmness is night and day. Skipped bench bleed; did one round of pedal bleed only. Also cycled ABS after first pedal bleed but did not see any additional bubbles. I believe pedal bleed is a must unless you've perfectly bench bled the new MC. Power bleed alone does not remove all air in a brand new (non-bench bled) MC. Just my 2 cents.

You all make it sound very difficult. All I did was to lift the car up high on the side of the master cylinder so the brake fluid couldn't run out of the ABS, changed the master cylinder, filled the reservoir, bleed the brake system with good old gravity and a child pressing the brake pedal when told too, lowered the car again and had no problems at all.