boxsey911

If you already have 993TT on the front what have you got on the back?

Bill Verburg

The issue w/ all the 996tt rear calipers is the small pistons that they use. They have 28/30 which are the same as the stock 964 4 piston rears. They do get some additional rear brake torque from the bigger 330mm rotors but not enough to balance the big fronts.

Doesn't matter whether you have 964RS fron 993RS front or 996tt front you will want the 964RS or 993 rear caliper w/ 30/34 pistons. These are the same caliper except for the part # and use a stock 964 rear rotor. You will still want more rear brake so the p/v should also be removed.

neffets

What about using 996N/A front brakes on the rear of the 964?

Bill Verburg

Not a good idea for 2 reasons
1) the 996 fron or the 964 front for that matter wants a rotor 26-28mm thick the only rear rotor that fits a 964 is 24mm thick so you start beneathe spec w/ new rotors
2) the bias approaches 1:1, ideal w/o p/v for a 911/964/993 is in the 1.425 to 1.525 range. No a p/v won't help , they only should be used on the back and they only reduce rear brake line pressure above a threshhold either fixed or adjustable, doesn't matter.

If you use a twin master setup then you can take car of the bias issue but not the thickness issue

neffets

What about this : use the two piece front 964 caliper, take it apart, mill off 2mm on each side, assemble make an adapter to fit it. (or use wilwood or similar with porsche stickers in the back)
And match up a big enough caliper/disc in front to get the correct bias?

boxsey911

Bill may I ask you if you have experience of the removed p/v in wet/low grip situations? The reason for asking is that a friend has a 964 with the recommended set up of 993TT fronts, 964RS rears and 993 m/c. With a 55 bar p/v he was getting lock ups of the rears in the wet. These were so violent that the car would swap ends even when braking in a straight line in the wet. So, with no p/v this would presumably have been even worse. He's since had an adjustable p/v fitted so that he can reduce the bias to the rear to prevent the rear locking before the front. For information front and rear both have standard textar pads and tyres have good tread depth (Dunlop DZ03 track tyres).

Bill Verburg

Sure you could do that, then you only have the bias issue to contend w/, to deal w/ that you will want a twin master setup as was used on the C4 l/w

Bill Verburg

He' got some other issue, I'd bet that w/ or w/o the p/v he would have the same thing going on. 55bar is still pretty decent line pressure, I don't know how hard in brakes in the wet but I'd be surprised if he was exceeding 55bar.

Lots of things can cause that, but it boils down to some issue in front or some issue on one side that doesn't allow line pressure to work the pads at 1 or 2 or even 3 calipers.

common things are rubber lines that are swollen internally, frozen pads, frozen pistons, debris blocking the lines faulty ABS, faulty ABS sensors etc.

boxsey911

Thanks Bill, that's given us plenty of ideas to look at.