nickyv

I have rebuilt my brake calipers, front and rear. On the rear I have the two piston small calipers. I've seen the post about switching out to the 4 piston calipers, but for me right now, rebuilding them fits the wallet better, a lot better. The rear calipers contained two 28mm pistons, the O ring, dust covers and snap in vibration dampeners. I believe they are referred to as mushroom style by several of you. When I ordered new parts, the vibration dampeners I was sent had very small mushrooms, or snap in apparatus if you will. Much smaller than the hole in the piston so they didn't snap in at all. not the size of the original dampeners that I removed. Just didn't work. I went to Sunset (dampeners came from Pelican) and the diagram shows a metal insert that goes into the hole in the piston and the insert contains a hollowed out section that these dampeners do snap in to. Sunset said Porsche made some changes over the years and this was the last updated change to this specific caliber. My caliper set up did not have this insert. All this brings me to my question. The insert drops into the piston and moves in and out freely. It fits perfectly, but still moves in and out freely. If I use this set up, it just seems to me with the dampener (has the peel away which exposes the sticky backing) is stuck to the back of the brake pad , when the brake is released and the piston retracts, the pad will not be pulled away from the disc. I say this because the insert that the dampener is attached too may simply slide out of the piston as it retracts because it is attached to the dampener which is attached to the pad. Make sense? Am I missing the obvious here? Going to try and post some pictures. Any feedback is welcome. Love this car, but an engineering thought process I do not possess. I am so close to finishing this project, my first DIY, but do not want to put these calipers on if I have to turn around and take them off. Going to flush the entire brake system when everything is back together. First pic is are the piston, insert and dampener. Second pic is it partially assembled. Insert slides freely in and out. Last pic is the dampeners package with part number.

Evil Bunny

I would not use the aluminium insert, just source a larger 28mm damper, they are available.

In the past I have seen the aluminium insert rust solid to the caliper piston.

http://www.eurocarparts.com/search/101339030

JasonAndreas

Have you seen the two TSBs covering this?

Brake Vibration Damper TSB-92

Brake Vibration Damper TSB-93

C24FUN

When I bought my '90 C2 back in 2001 it still had the stock 2 pot rear calipers. I was driving and tracking it a lot back then and I went through the first couple of brake pad changes with the original calipers. I remember having similar confusion with the shims, damping plates and pads (all different from the front) but, like you, I had other priorities for my Porsche hobby dollars.

In 2004 I finally got around to swapping the rear calipers for a pair from a '96 993. It was a super simple job (direct bolt on) except for a bit of contortion required to swap out the rear biasing valve (near the ABS module in the frunk). Now the pads are identical to the front. braking is more reliable and when I go to the track nobody points and laughs at my "puny, wimpy rears brakes" (OK that part didn't happen, but I no longer suffer from "caliper performance anxiety").

Anyway, looking around it seems used 993 rear calipers are pretty easy to find at a reasonable price (~$400/pair on eBay) so I highly recommend it as one of the cheaper 964 upgrades when your budget permits.

Cheers!

Jim G.

Bill Verburg

The 964 2 pot rear calipers uses 2x44mm pistons per caliper,
the vibration damper is a 2 piece assembly, the damping plate used to have the piston size stamped on it, for your rears it would be 44S, 4pot 964 is 28S & 30 S, your 2 rear pistons are the same size as was used on a 965's larger front pistons, the plate is id'ed and sized to fit only the piston cavity specified.

so for you rear per caliper
2x 965.351.096.00 (Porsche is unclear about this but I believe it to be what you need, these are the 965 large fronts)
2x 964.352.963.01

your fronts would be per caliper
x2 964.351.096.01 (36mm)
x2 964.351.096.02 (40mm)
these are all the newer 23mm deep versions

a 964 4pot rear would be per caliper
x2 964.352.096.01 (28mm)
x2 964.352.096.02 (30mm)


All that said I never use them, they are a PIA and waste of $$.

Bill Verburg

The 993 rears are a great upgrade to any 964. They use the same pad and rotor as stock 964 but the increased piston size gives the car much better bias

964 bias desirability in order best to worst
964-4/993-4
964-4/964-2
964-4/964-4
964RS

nickyv

Thanks for the feedback. Thanks for the TB's Jason. They don't really address the issue I see. I don't see any mention of adhering the insert to the piston. My rear pistons were labeled 28mm and they fit the caliper perfectly. Just not seeing why the insert will stay within the piston when the piston retracts. The insert is attached to the mushroom which is attached via the sticky side to the brake pad. I'm not exactly comfortable just "trusting" it will work. It's not like I'm fixing the radio. I'll let you know how it goes. Damn project has taken me forever, losing all my good AZ driving days.

Harry Apps

How far do you think the pistons retract when you release the pedal? The pads should always be just/almost touching the rotor and only retract when you do it manually.