rbauhart

Hello all,

I track an RS America, and have a question about the following brake setup:

Front - Big Blacks with 332x32mm slotted rotors
Rear - 993TT calipers with 322x28mm slotted rotors

My question is, do I upgrade the master cylinder or remove the proportioning valve and leave the MC. The stock RSA MC is 20.64mm, and the 993TT MC is 25.4mm. I have been told that the setup will work well by leaving the MC and simply removing the proportioning valve. But also that the MC should be upgraded, and possibly a brake booster added, and the PV should be left alone.

Leaning towards removing the PV and leaving the MC at the moment. Any thoughts?

Thanks a lot,

Roland

Bill Verburg

You can't do that unless you are willing to give up the parking brake

for a race car where the parking brake is not needed, you would need a 322x28mm rotor/hat assembly similar to what 993RS/tt use in front. Personally I'd prefer the RS caliper but tt works just doesn't take up it's fair share of braking work.

If parking brake is needed then the best choice is stock or 951 M030 rear rotors(the 951's are what was used on 964RS) w/ either 964RS rear calipers or 993 rear calipers(they are the same)

w/ any of the above bbk mods you want a 23.8mm mc or even better 25.4mm. For the 964RSA this means changing the m/c to a 993 version(you need to change the booster too) or swapping in a C4 electro-hyd. setup. If you retain the stock RSA 20.6mm m/c you will have a relatively mushy pedal and a longish throw

w/ 964RS or 993 rear calipers or w/ 993tt ditch the p/v. If you use the 993RS rears i'd leave it stock

rbauhart

Bill. Thanks for all the input. You definitely know your brakes!

I have already decided to give up the parking brake. That is not a concern any more.

I am going to a 993TT rear caliper. I see what you mean by the 993RS rear caliper with the difference in piston size.

As far as I can see, from what you have said, with the 993RS rear calipers, one would keep the PV, and with the 993TT rear calipers, one would get rid of the PV? But either way, the MC should be upgraded and a brake booster is needed?

Roland

Bill Verburg

correct,
993parts needed to upgrade the m/c to 23.8mm
m/c 993.355.910.00
vac can 993.355.023.10
gasket 993.355.301.00
m/c support 993.355.163.03

you will also need to address the issue of 12mm 993 fittings vs 10mm 964 fittings, either new lines or 1x10mm adaptors are needed or BMW 10mm to 12mm brake line adapter part #
34-32-6-752-405

rbauhart

Bad idea to upgrade to the 25.4mm 993TT m/c?

993-355-903-00

Bill Verburg

Au contrere, just a lot more difficult to do the electro-hyd transplant

rbauhart

Parts seem a lot less expensive for the 23.8mm 993m/c compared to the 25.4mm 993TT m/c as well.

So, this setup with 993TT rear calipers, a 23.8mm 993m/c, no PV, and maybe running pagid yellows up front and pagid blacks for more bite at the rear will probably give pretty good rear bias I am guessing. Seems like that will be a good way to go.

Roland

Bill Verburg

yes, personally I'd prefer more rear but given the 2 choices, that's going to be ok.

If you get real ambitious you could have the trailing 2 piston/holes machined to 30mm as a compromise or go to a dual master setup as used on the later Cup cars & 964RS/lwt
bias
tt 28/28 2.061
modified tt 28/30 1.919
modified tt 30/34 1.572
RS 30/36 1.472
I very much prefer either of the latter 2, none of the first 3 want a p/v for most setups

rbauhart

Thanks again for all your help Bill. Great information.

Roland