PC2

Anyone know where I can find a write up/procedure on upgrading the 2 piston brake calipers to 4? Is it a very straight forward DIY job or should I leave it to my wrench? Other than the calipers are there other parts I should be getting. Thanks in advance.

garrett376

Isn't it a direct bolt on??? From all the stuff I've read, I thought it was....

PC2

I read the same thing about S4, and Turbo brakes. But nothing on going from a 2 piston to 4. I just wanted to make sure so I don't make any fatal errors.

JasonAndreas

Porsche suggests that you replace your rear brake pressure regulator (bias valve) with part #964.355.305.10

nine64

I did the upgrade and it's just bolt on. However I didn't change the rear pressure regulator, i will also order the part and change it.

garrett376

Jeff Curtis has mentioned that a little more rearward bias is not a bad thing (I think he's the one that mentioned that...) especially for a car used on the track; I'd think that changing just the calipers would not harm the overall balance, but maybe improve it. Someone please confirm with fact!!!

Jason, what is the bias of that part number you listed?

JasonAndreas

The switchover pressure is 55bar, the bias valve that came on cars equipped with 2 piston rear calipers is 45.

Bill Gregory

Changing over to the 4 piston calipers is a bolt on, and you should, as mentioned, also change the bias valve to the 92+, which would then be the factory configuration. Some people with 4 piston brakes all around, who use their 964's on the track, have found that going to the Turbo 60 bar bias valve provides additional stability under heavy braking.

nine64

Bill,
mostly street use for me, would you suggest that i use the turbo bias valve?
part no.?
thanks.
10

Bill Gregory

For mostly street use, the 92+ stock 55 bar bias valve will work fine.

PC2

nine64,

Do you remember where the part numbers are printed on the calipers? I'm going to LA dismantler (Porsche grave yard) to pick them up and just wanted to make sure they are the rear calipers and not the fronts. Thanks!

Bill Gregory

As I recall, fronts have a 964 part number, and rears have a 928 part number. Since I no longer have stock brakes, I can't check the casting number on the caliper, perhaps someone else can.

nine64

Peter, here is the part no. that i use.
left rear caliper is 928.352.421.03 and right rear is 928.352.422.02.

PC2

Thanks guys!

nine64

Just install the bias valve, took my OPC about 15 minutes, part and fitting come out around 100 usd.