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Is there a sort of mark, stamp, or casting change, to tell the difference between a stock 987 master cylinder and one from a GT3?
Got to run my car back-to-back with a friend's car last week. His car, for sure, has the GT3 master. My car is *supposed* to have one but I have no proof it was done. Our cars are set up the same as far as brakes go: same fluid, pads, cooling setup, etc. His pedal was more firm and confident.
It could be that I need to bleed mine again (tho it's on a fresh flush... always possible there's a little air trapped somewhere that shows up once things get hot). But before I do.... I did slide my phone under the master on both cars and snap a pic... and they're stamped differently.
My car has "12" followed by "7 ALTUR 1973".
His has "15" followed by "8 ALTUR 1973".
If it turns out I *don't* have a GT3 master, then I'm going to order one and install it vs. mess around with bleeding and using up another bottle of SRF.
Last edited by User 52121; 08-01-2018 at 02:40 PM.
I've been waiting for a knowledgeable answer to your question too. IF this is any help, I bought the "in between", the master cyl from the PCCB version. Larger bore than stock, not as large as the GT3. (#997 355 910 10) Mine is stamped "14" followed by "8 ALTUR 1973". The stock 2009 CS is marked "08" "8 ALTUR". My suspicion is that these numbers are merely casting dates; Altur is a Romanian company who makes aluminum castings.
I think that we'd need to measure the bore directly. That weird snap ring has me flummoxed though so I gave up.
I looked at Johns original master that came off the car it has the markings 07 followed by 7 altur1973. The first marking is most likely the year of manufacturing. the second number may be the identifier as it matches your master.
The one I installed (TRW PMN166) looks externally different. Big difference in pedal feel.
Factory on the left, GT3 installed on the right. Note the two machined circular areas on the top of the installed master cylinder.
The one I installed (TRW PMN166) looks externally different. Big difference in pedal feel.
Factory on the left, GT3 installed on the right. Note the two machined circular areas on the top of the installed master cylinder.
I just looked at Johns car. As above the gt3 master has 2 machined circles and the original only has one. Good eye. I would also add the 23 on the stock master probably signifies the 23mm bore size of the stock master.
I just looked at Johns car. As above the gt3 master has 2 machined circles and the original only has one. Good eye. I would also add the 23 on the stock master probably signifies the 23mm bore size of the stock master.
Awesome thanks Mark and tweej. I will investigate this when I get home tonight!
Confirmed the master in my car has the two machined circles
Depending on how and when the last time you had the fluid changed, if you're not happy with the pedal feel I'd take it to a specialist shop and have them do a brake fluid flush and bleed. After a fluid change, I have never been able to reproduce the results my shop gets when I bleed myself. Also, while Castrol STF is a popular fluid for its high boiling point, it's actually pretty compressible when it's warm so you might try a different fluid. I'm happy with Endless RF-650 right now.
Another contributing factor might be brake pad thickness. My street pads are a couple of mm thinner than the pads I use on track and I can feel the difference in initial pedal travel. The feel with the GT3 master cylinder and street pads is still way better than with the original 987 master cylinder.
08-01-2018, 12:29 PM
GT3 Master - how to tell?
