UKKid35

I have just removed the early S4 calipers and fitted refurbed later calipers. Are there any differences due to the piston changes that I should bear in mind?

Jim M.

IIRC the late rear calipers had 36/30 pistons and the early had 30/28. Everything else, the pads, brake bias valve, and the master cylinders were the same so there should be no problems. I believe the pistons were changed to make the pad wear more uniform. As with most things Porsche the newer the better.

UKKid35

Don't the larger rear pistons shift the bias towards the front brakes?

Vilhuer

Seals are different style. Changed in mid '88 MY IIRR.

Jim M.

No I think it would move it towards the rear, at least I think so, but on the USA cars the brake bias valve remained at 18 BAR. It may have been an evolutionary change where the factory wanted more rear bias. Either way the piston and seal changes were all that was done AFAIK.

blown 87

I am doing this same thing on my 87, going to 89 fronts and rears.
Just got the last one off of the donor car, getting them ready for paint.