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.

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.

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

So the ebay adapter didn't work for you?

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

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.

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:
https://cimg9.ibsrv.net/gimg/rennlis...388e73c010.jpg

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?

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...