What brake line sizes are on the GT3 master cylinder
 

There seem to be 2 sizes - certainly for the nuts. What are they?

Thanks

Ray

i believe they are 10mm and 12mm

Correct...one 10mm and one 12mm. I used an adapter on the 10mm to install a 997 GT3 master cylinder, an excellent upgrade.

Great!

Thanks - what does the 997 MC do? I am guessing that the brake bias changes. FWIW I am running the 350mm rear rotors...

Thanks

Ray

I did not notice any significant changes in bias. It reduces pedal travel by quite a bit which is the main benefit...I think it feels alot better. Bore size is slightly larger at 27mm.

Here's the thread where I show how to modify the adapter to work. I used this on my 996 C2, then moved it to my 996 GT3. Works great I have done track days in both cars with it and love the results. https://rennlist.com/forums/996-foru...my-996-c2.html

No change in bias. The piston in the 997MC is larger (27mm vs. 25mm on the 6GT3) and the ports are both M12. You don't need to complicate things any adapters whatsoever Ray, nor do you need to fabricate a custom line. You simply need to install an OEM Boxter M12 brake line in place of the M10 GT3 one. Most people don't know that the Boxster MC uses M12 ports front and rear so the Boxster rear brake line makes this all plug and play. You can get the brake line on ebay for a few bucks or from the dealer for under $20. It's the one used on a 96-99 Boxster with ABS without PSM. You can see it here on my car, it's the green one.

Thanks John,

My real problem is that I want to plumb in brake pressure transducers... Was unaware of the MC upgrade. As it is, I am fine with pedal feel, not to happy with the ABS unit, but that is another story https://rennlist.com/forums/images/icons/icon9.gif

Ray

Good info I will order one and get rid of the adapter. Thanks for the info. It looks like the part number for this line is 996 355 313 04. I will order one and report back.

I believe the 996 GT3 Cup cars used a dual master with adjustable pressure/bias front to rear. If you can get your hands on one of those.

Thats incorrect. The 996 Cup uses the same master as the street car, the 25mm one with a 12/10mm port. The MC you reference above is found on the 997cup which does not have ABS.

Cool thanks for clarifying. I was looking at a couple 996 Cup cars this past weekend at the track, they must have both had the 997 setup retrofitted.

About Boxster circuits :
Well, I can confirm with 100% that my 2001 Boxster S, (OEM) has the rear circuit outlet of the MC in M10 !
(front outlet is M12)
May be is because of PSM, as the 10mm outlet goes to the passenger side, to the PSM pump.

Parts catalog shows a part number split in 2001 for the Boxster line, but that's for the Non-PSM part. I also know that 996's without PSM have 2 M12 ports on the master cylinder so maybe the part is the same on non-PSM 996.1's too. I will check the 996 catalog later and see if the P/N is the same as the Boxster P/N I posted above, I'd betcha that it is on non-PSM cars.

With PSM in any case you will need to either custom make a new line with an M12 end, or use the brass adapter.

Yes, the street ABS units suck. That is why I swapped in a 996Cup ABS. The motorsport ABS is night and day, probably one of the best mods I've done to the car. I use that with the 997GT3MC, the 997GT3 engine cam driven vacuum pump, 996GT3 vacuum booster, the 997GT3 380/350 calipers, and 380/350 AP Racing floating rotors. This set up is phenomenal...

If you want a brake pressure transducer set up, I can post up pics of what I'm using. I consists of a banjo bolt set up mated to a Motec pressure transducer..