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So was swapping rotors and pads today and the pistons look like nothing I’ve ever seen before. Instead of the traditional piston I’m used to, they looked narrower with this “hat” on them.
And upon using a spreader to get the pistons back into the caliper to put the new pads in, this piece broke off the outward side. Now when pushing the brake pedal, fluid comes out of the that side. Not sure if this repairable with a rebuild or if I need to buy a new caliper?
note the shim/backing plate has two cylinders attached to it that fit inside the pistons. getting pads out with the caliper attached to the hub may be very difficult if the shims are pried away from the pads first (sometimes they are glued to the back of the pads). there is simply not enough room to get them out otherwise, IME. in many cases people remove the caliper from the hub to remove the pads along with the shims.
it looks like that "hat" you speak of is a shim that managed to stay in one of the pistons when you removed a pad and then fell out as you applied the spreader. (i'm just guessing here).
why is it leaking? i suspect you may have damaged a piston seal upon re-assembly. again, a guess.
BTW, when i recently replaced my pads and rotors, i simply cracked open the bleed screw on the caliper to facilitate pushing back the pistons to remove the pads, once the backing plate/shim had been pried loose of the pad. it's much easier to push them back due to the small amount of fluid and short distance between the piston and the bleed screw. it can practically be done by hand.
incidentally i had no need to remove the pistons (two on each side on mine) or touch them in any way when replacing pads and rotors (YMMV) so i can't say what might have happened if they had been removed for some reason.
Last edited by hueyhoolihan; 11-25-2021 at 09:50 PM.
note the shim/backing plate has two cylinders attached to it that fit inside the pistons. getting pads out with the caliper attached to the hub may be very difficult if the shims are pried away from the pads first (sometimes they are glued to the back of the pads). there is simply not enough room to get them out otherwise, IME. in many cases people remove the caliper from the hub to remove the pads along with the shims.
it looks like that "hat" you speak of is a shim that managed to stay in one of the pistons when you removed a pad and then fell out as you applied the spreader. (i'm just guessing here).
why is it leaking? i suspect you may have damaged a piston seal upon re-assembly. again, a guess.
Appreciate the response (and Happy Thanksgiving!). I’m sure your guesses are right. So maybe a quick caliper rebuild will resolve my issue? I swap pads regularly as this is a track car - is the shim necessary, as I came from a 981 which didn’t have such a thing.
can't say for sure about the necessity of the shims. all i know is that they are supposed to suppress squealing, which may or may not of interest to a driver. i have shims on both my sports cars and neither squeal. i can't think of any reason why braking would suffer due to their absence.
and if the problem is indeed a damaged piston seal, a rebuild kit should do the trick i would think.
This is the item. It's a brake pad anti squeal shim. The metal part spring clips into a hole in the piston. The other side is adhesive and sticks to the brake pad backing plate.
If you are going to be swapping pads often for track use then you wouldn't want to use these. They are not conducive to removal and reinstallation.
Are you sure the brake fluid is leaking from the piston?
There is a little o-ring that goes in a channel inside the caliper bore (not pictured) and then piston goes in with the pictured dust boot installed under the collar on the piston.
I find it hard to be believe you did anything to damage the piston o-ring to cause a leak.
To confirm I'd remove the caliper from the rotor, remove the pads, and place a wooden block in the caliper and have someone step on the brake pedal while you check for fluid leaks.
Make sure the wood block is in there and thick an long enough to keep the pistons from coming all the way out of the bores or you will have a real mess.
I’ve gone out of town for the weekend, so will be sure to check when I get back. I noticed the fluid leaking when pressing the brake after I had put it all back together and ran out of time to take it back apart.
Confirmed that the top piston seal on that right rear caliper has died, as that's where the fluid is coming from. Off to shop for a rebuild kit, and thanks again for all the knowledge gained!
11-25-2021, 08:38 PM
987.2 Cayman S Rear Brake Caliper Help
