slips2

I want to upgrade my 1990 C2's rear 44mm 2-piston brakes to 993 NB standard rear brake calipers with 30/34mm pistons. I have a caliper pair shown below that I think are the correct ones, but before I slap them on, I would appreciate confirmation from a keener eye than mine. The castings are stamped with big 95 numerals in a recessed circular area, and then just below the 95s, one is stamped 20.4673.00 and the other 20.4672.02. The portion of the pistons visible outside the rubber seals are diameters 27mm & 30mm with center holes 14mm & 18mm.



I've just finished lowering my C2 by 35mm at all four corners with H&R Red springs & Bilstein HDs, and have installed 7- & 9-inch Meteor Gray Metallic Cup IIs fitted with Michelin 225/45ZR17 & 255/40ZR17 PS2 tires. With the lower center of gravity & stiffer springs (less weight transfer forward during braking), and the larger tire contact patches in the rear, I propose leaving the original 45-bar brake porportioning valve in place. Is this sensible given the slightly rear brake bias over stock, i.e the 6% increase in rear brake piston area?
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Bill Verburg

if the holes where the spiders clip in are 15.mm & 12.5mm, then the pistons are 34/30

slips2

Thanks Bill ...

I re-checked the spider holes and they're 14 & 18mm ID. I also measured the diameters defined by the "ridges" in the rubber seals, thinking they may approximate the piston diameters on the hydraulic side. They are 30-31 & 34-35mm, so more than likely they're the 30/34 993 calipers.

No need to change the PV for the 6% increase in rear caliper piston area, given the more capable rear braking - a product of the lesser forward weight transfer under breaking and the increased rear tire contact patches?

sundog

When I did this I changed the proportioning valve for a couple of reasons. First, the brake pad area is significantly larger, and the piston are is slightly larger.

Secondly, if the Porsche engineers thought it prudent, then I won't argue with their wisdom.

I track the car, and the braking is very well balanced with this setup.

boxsey911

Aren't those the part numbers that I can see just peeking out on the right side of your pic above? If so the part numbers according PET are 993 352 421 00 (left caliper) and 993 352 422 00 (right caliper).

slips2

Which PV did you install?
This was for the stock 964 front calipers, with the 993 or 964 4-piston rear calipers?

No, those numbers you see in the picture are the casting numbers for the caliper frame(s), as listed above in my first post. The rear of each caliper is stamped "brembo", but no Porsche part numbers appear anywhere on these calipers.

boxsey911

Thanks for clarifying that. The last time I took my calipers off I don't remember seeing part numbers on them but your picture made me wonder if this had changed on 993 and later calipers.