Problem with 996 TT Calipers on the Rear (964)

[SvnS3]

Hello Guys, Iīm from Germany, so please forgive my bad english.

I want to fit the complete 996TT Brake System to my 89ī964 C4.

The front is not a problem, but the rear. People told me, that the handbrake wouldnīt fit with the 996 TT Rotors.

Is there a solution i donīt know?

Thanks a lot

[Bill Verburg]

Originally Posted by SvnS3

Hello Guys, Iīm from Germany, so please forgive my bad english.

I want to fit the complete 996TT Brake System to my 89ī964 C4.

The front is not a problem, but the rear. People told me, that the handbrake wouldnīt fit with the 996 TT Rotors.

Is there a solution i donīt know?

Thanks a lot

I'm not sure why you want to use the 996tt brakes on your 964 they have horrible bias.

Just some facts to give you perspective
all 911 thru '83 have ~1.891 f/r bias w/ no proportioning valve
964 has 1.793 f/r bias w/ a p/v that further moves bias to the front, you can improve 964 brakes by removing the p/v
964RS has 1.713 f/r bias w/ p/v that moves the bias further forward, again remove the p/v for an improvement
996 has 1.811 f/r bias again too far forward
996tt has 2.084 f/r bias too far forward
The best bias is seen on the original 911 and on the 993RS w/ 1.426 f/r bias

so the best of the admittedly poor choices for a bolt on 964 big brake kit is to use either 964RS/3.3t or 993RS/t front calipers on the 964 RS 32x322mm rotors(alternately use 928GTS front rotors which are the same but not drilled) in back use 993 rear calipers on the stock 964 rear rotors(alternately use 968M030 rear rotors which are the same but have axial holes). remove the p/v and also use 993 vacuum boost and 23.8mm m/c(unless you have a 964C4 which already has a 23.8mm m/c)

This setup has ok bias, ok pedal, and is used by most 964s w/ big brakes

[SvnS3]

What means P/V ?

[Bill Verburg]

Originally Posted by SvnS3

What means P/V ?

p/v proportioning valve - these are used on the rear hydraulic circuit to reduce brake torque in back above a threshold, stock p/v on a 4/4 piston 964 is 55bar .46 reduction stock w/ a 4/2 setup is 45bar w/ .46 reduction

The only reason that I can see to have these is that Porsche was afraid of law suits. What they do is drastically reduce rear brake torque to the point that the rears are hardly doing anything, the car will always go off the road front end first w/ this setup. If you have ever driven a '69-83 911 that is what great bias feels like.

[SvnS3]

I have the 55 bar. Or not?

Is it right that I have to remove this ???

[Bill Verburg]

Originally Posted by SvnS3

I have the 55 bar. Or not?

Is it right that I have to remove this ???

If you have 4 piston rear then yes, you have a 55bar p/v

You don't have to remove it but you can get more out of your rear brakes than the p/v allows

[SvnS3]

Sounds good. And what I have to do, to get more out of the original p/v ?

[Bill Verburg]

Originally Posted by SvnS3

Sounds good. And what I have to do, to get more out of the original p/v ?

You will find the p/v next to the ABS pump

Here is one disassembled


Take out the guts and reassemble, voila no more p/v