josephsc

So I was doing brake inspection on my 951S -- the first time since I got the car. I was getting frustrated with one of the pistons not opening back up to let me insert the brake pad, so I took the caliper off and this is what I found. Basically, the caliper would close but not open back up -- so it's fully closed now....

Does anyone have any idea what's wrong with this? Can it be rebuilt or repaired? Or shall I start looking for a replacement?

Yabo

Sorry, not quite understanding your description... is it the pistons on the right in your pic or the ones on the left that are not working?

Skunk Workz

Probably gotten the piston so far out it's misaligned in the hole...you need to "wobble" it to make it go straight in the bore. Or,it could be that you've gotten some muck in there that needs to be cleaned out to make the piston slide back in.

Peckster

Why would you take the pads out to inspect them? Was there anything wrong with your brakes before?

83na944

I don't have any experience with dual piston calipers, but...

I think that the pistons should free to move when there is no hydraulic pressure on them. When the caliper is connected, I can see how pressing on one piston might cause the other to extend.

The pistons should fit pretty tight, so they shouldn't get misaligned in the bore, unless they are overextended.

Can you press the piston back in now? Shouldn't there be a dust boot around the pistons?

josephsc

Thanks -- I'll try that.

Right now, the pistons are just stuck in place -- but it's possible that its the symptoms of another problem. The reason I went in there in the first place was a strange uneven brake pad wear - the stuck side wasn't worn as the other side.

Any other comments would be appreciate it -- I'm sort of stuck here...

Yabo

C Clamps, squeeze them back in, may take a lot, as in maybe an extension on the handle, of force, and they should eventually go in.... Then hook it back up and see if it works.. if not, you are gonna need to rebuild!

josephsc

Welp.... I've figured out one thing. The pistons are not sitting in there straight. I've already tried c-clamp, pry bar, and a el-cheapo disc brake spreader and no go...

I suspect that the pistons became misaligned because the force wasn't being applied evenly around the piston and I used too much force trying to push them back. Crap....

Sam Lin

First pull the anti-squeal shim out of the pistons so you can get a good look at it. Post a pic after you do that.

Sam

josephsc

Done that -- here's a pic of one unhappy piston...

Sam Lin

Yeah, it's cocked. Take brake cleaner and a toothbrush, and as it sits now, clean the piston and seal as best you can. Be liberal. You want that entire area as clean as you possibly can get it. Then you can grab the piston with a clean hand and wiggle it to try and straighten it. If it won't push straight, then wiggle while pulling it out, and just remove it. It will be very difficult to move at first since you tried to force it.

If you can't get it to budge with force, then pad the piston with a clean rag, and then using a block of clean wood, tap lightly on the piston tip with a hammer to get it to straighten. Then pull it out.

At that point post pics of the piston and bore, since there's likely damage as a result of you trying to force the piston in.

Sam

josephsc

Thanks Sam -- I knew pushing out the pistons were supposed to require some force, but I guess I got a little too excited.

Peckster

Here's hoping you didn't damage the bore or piston trying to force it back in at an angle.