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Discussion Starter #1
I'm attempting to change my brake pads and while the caliper was removed and I was away, my son decided to pump the brakes. I think the piston got pushed way too far out because I cannot get it back into a reasonable position using a C-clamp. I've included pictures of both front calipers (the good one and the bad one) to show the difference. I though it would be a good idea to attach my hand-operated vacuum bleeder to the bleeder valve and open the bleeder screw a quarter turn to provide some relief in case the pressure was keeping the piston from compressing. It moved a mm or two, but not enough to get the caliper back on.
Any suggestions for getting the piston back into place? Barring that, any suggestions for getting this fixed professionally? If there is a simple way to detach the caliper and drive it to a garage, I'd like to know what it is. I'm not enthusiastic about trying to get my whole car onto a tow truck when I can't even get the caliper reattached.
Thanks in advance!
 

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Discussion Starter #3
You are correct; it is not squared up properly. You can see it a bit in the picture. I tried using my C-clamp on the outermost lip of the piston in the hope of forcing the worst-aligned point back into a square position. No dice.
 

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Try using a block of wood and a hammer to pound in the side that out too much to square it up.
 

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Calipers can be rebuilt by replacing the piston seal , although no one does this anymore.

You need to square up the piston first by pulling it out slightly ; then block of wood idea might work.

The piston seal may have swollen slighty and be preventing piston from retracting easily.
New caliper is the best option, if you know how to bleed brakes.

Tearing off seal that is around the inside of travel piston might help; it is designed to keep dirt out of inner caliper but doesn't actually hold fluid pressure. Fluid pressure is held by an Oring.
 

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Discussion Starter #6
Thanks for all the feedback. Here is the latest:

I was able to loosen the piston such that I can now feel it float freely when I manually manipulate it. The new issue is getting the piston back into the caliper. I laid the old brake pad across the mouth of the piston and tried using the C-clamp to get it back in. That's when some brake fluid leaked out. I assume that means that the internal O-ring is damaged. Can anyone confirm or deny this? If the O-ring is damaged that must mean that it is "game over" for this caliper, right?

If the caliper is broken, can anyone advise me about removing it? In the "piston_bad" photo I included, you can see a nut that appears to connect the rubber hose to the back of the caliper. Is this the key to removing the caliper?

The above post is a chain of several assumptions. Going back to the beginning...if it is normal for brake fluid to leak while trying to re-compress the piston, please let me know.
 

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Do you have the bleeder screw open? The fluid needs to go somewhere.

But at this time it appears a rebuilt one from AutoZone is the best bet. You will need to get some brake fluid too.

Go and get the caliper and fluid, you can bring your old one back for the exchange.

Loosen the brake hose just a bit to make further removal easy but leave attached. Then put the new caliper and pads in place. Swap the hose over. Bleed the brakes.
 

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Discussion Starter #8
Well that didn't take long. I went out to show my daughter how the brake work was going and I saw that in 20 minutes, the brake fluid pressure managed to push the now-loosened piston almost completely out of the caliper. When I picked up the now-loose piston, the rest of the brake fluid came streaming out. Following some clean-up, I now have a piston completely liberated from the caliper (picture attached).

Maybe this is a stupid question, but should the piston go back into the caliper easier now that there is zero push-back from the brake fluid? Is it wise to even try this? Is the O-ring damaged beyond hope? Maybe I'm a pessimist, but this caliper sure looks broken.
 

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Well it just pushes back in as long as you go squarely. If it doesn't leak then you are OK. If it does then you need a new one.
 

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few tips for you:

- judging by the pic, you had the piston partway out. that's why it wasn't square and was resisting going back in. probably popped it out with fluid pressure on disassembly or while you were serving the caliper.

- yes you can rebuild calipers, but good luck getting a rebuild kit. just save yourself the hassle/time and get a reman'ed caliper or a new one if you don't like refurbs.

- always inspect your boots thoroughly while you have the caliper out. a boot with even a slight tear would cause the piston to seize over time as crap gets in.

- the caliper is not necessarily toast, i've done this job many times. that piston looks well fouled though. that black buildup is what caused your problem. it's easy to clean, get some 400 grit sandpaper and clean it off by hand. that grit level is quite fine and will not harm the machined surface but is enough to make the job easy. you'll have to do the same to the bore as well

- the seal inside the bore can be visually inspected. do so to see if you're up for a new caliper. you can put some caliper grease on the piston itself to make things go back together easier. don't forget the slide pin(s)!

- getting the piston back inside the boot can be a total ass. sometimes you can pull the boot up by hand and work it around the piston. don't use tools that could puncture it.

- finally, get yourself one of these to make your life easier:



here's how its used, that's an old brake pad being used on the piston since its hollow...screw doesn't have enough length for that. just don't reuse the pad after this kind of abuse.

 
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