freedman

Apologies in advance, I know there are a lot of brake posts on here, but I have looked and cannot see anything about this option

928 GTS rear calipers have 30/28 rear pistons and 322mm discs (I believe)

Do you actually need the bigger discs? and are these a reasonable upgrade, in comparison to a 993 caliper say

In conjunction with 993/S4 fronts

Bill Verburg

The 928GTS used the same small rotors as a stock 964 or 964RS
the 964RS caliper used the bigger 30/34 rear pistons to balance the bigger front brakes.

if you have 993 front calipers on 304mm S4 rotors(or the bigger 322mm RS rotors) use the 993 rear calipers on the stock or RS rear rotors(these are actually off a 951 M030 )

to use the bigger 322mm custom rotors on the back of a 964 you need a hat/annulus setup that eliminates the parking brake, for this setup you use the 993RS rear calipers and 993RS/TT big red fronts on 322mm rotors. This is a great track setup, I jsy got back from WGI where a hot rod 964 owner had just installed the 993RS set on his car, he was raving about how good the brakes are but had to readjust his technique because of the additional brake that was now available.

freedman

Thanks Bill

So no need to change the discs, is there any value in changing to those calipers as they have bigger piston area? (and do they use the bigger pad as per the 993 front as well?)

boxsey911

Those pistons are the same size as the standard C4 rears which I assume is why Bill is suggesting the usual alternative of putting 993C2 rears on standard 964 or 964RS rear rotors.

Bill Verburg

for the back of all 964 except turbo, use either the stock 964 rear rotors or the 964rS rear rotors. These are all 299x24mm, the difference is that the RS uses drilled, but still straight vane while the regular cars use plain straight vane

the 964 RS rear rotors are off of 944/951 M030 option car, part# 951.352.041.91, both left and right are the same part.

when changing the front to either of the common b/b fitments(either 993RS/TT or 993 on 322 or 304mm rotors) you need to change the rear calipers and the m/c too to have it right and as effective as possible.

the 993 rears are the same except for part # and some cosmetics as the 964RS rears. These both have the bigger 30/34 pistons as compared to the 28/30 used on 4 piston rear stock. 928 and 944/951/968 all used the same small 28/30 on the same small 299x24 rotors. The only 964 to use the 30/34 besides the RS was the turbo, this used a wider version of the same small caliper as the others but w/ 30/34 pistons to match the 993 size fronts on 322s. This caliper is incompatible w/ 964 rear due to the width of the rotor it wants, 28x299mm, and the o/s used to accommodate that rotor

This is still not the ideal setup, just the best that can be accomplished while retaining the parking brake and using stock parts.

do change the m/c to a 993 setup unless you have a 964C4 which already has the bigger 23.8mm m/c