Major problem with caliper piston...

[adrondube]

I'm simply replacing the brake pads on my mom's 2000 Buick Park Avenue...not a big deal right? I found how-to videos online...seemed pretty easy. Okay, so I have the caliper off and have to return the piston back inside its chamber to make room for the new wider brake pads. THIS THING IS NOT MOVING. I even bought an automotive/industrial strength 6 inch C-Clamp and it's NOT moving beyond it's current position (I'm using the older brake pad to make sure the pressure is spread out over the surface of the piston). I've tried bleeding the brakes to help...NADA. I'm at my wits end. Mom doesn't have the cash to take it to the shop. How hard can this be? I've even read where sometimes you can return the piston with the palm of your hand with adequate pressure. I've even tried hammering the turning bar on the C-Clamp and it's like the clamp is going to break...it's FORGED steel, very thick. What in the WORLD is going on? It should be easy to get back in its chamber!!! Can anyone help or offer any advise. Thanks-

Best Regards,
-Adron

[vgames33]

Sounds like the piston is siezed. If all that effort didn't make it move, I'd replace the caliper. I think you're supposed to replace them in sets. They shouldn't be more than 25-30 each for remans.

Did you try moving it with the bleeder screw open?

[adrondube]

Originally Posted by vgames33

Sounds like the piston is siezed. If all that effort didn't make it move, I'd replace the caliper. I think you're supposed to replace them in sets. They shouldn't be more than 25-30 each for remans.

Did you try moving it with the bleeder screw open?

Thanks for the reply. At first, atleast the caliper piston moved a little bit, but it would NOT move after like a few mm of length back into the chamber. I've tried having someone push in the brakes to try and release it, but it's not working. Loosened the bolt where you can bleed the brakes, didn't help. I am wondering if I should assemble eveything back and try the other side just to see what it does prior to taking this thing to the shop. Also, I've read that some caliper pistons SCREW IN versus just going back in under pressure. GREAT! It could be a screw in and I could have messed it up! All of this from trying to save my mom from a huge repair bill! YIKES! Thanks. I am about out of ideas and getting tired of trying to Google this for the last 2 days...UGH!

[adrondube]

Originally Posted by vgames33

Sounds like the piston is siezed. If all that effort didn't make it move, I'd replace the caliper. I think you're supposed to replace them in sets. They shouldn't be more than 25-30 each for remans.

Did you try moving it with the bleeder screw open?

yeah, i tried that. tried tapping the brakes in the car as well to see if it would loosen up again. at first, it was loose, but it just wouldn't go back in. after the c-clamp, it has kinda seized up and now it won't move AT ALL. any more ideas? if it turns out that it's a screw in kind, i'm screwed!

[Selectron]

I recall having that problem on a Russian-made Lada Riva, many years ago. The piston refused to push back in (with the bleed screw open), so I got my little cast-alloy G-clamp and gave that a try but it just snapped into two pieces, haha.

I seem to remember then closing the bleed screw and using the brake pedal to push the piston out by a couple of millimetres, then opening the bleed screw and, because I no longer had a working G-clamp, I used a motorcycle tyre lever (small, all rounded edges) to lever the piston back in to where it was previously. I think I must have put something else in there to fill the gap to give me something to lever against but I can't remember the details. Then I closed the bleed screw, used the brake to push the piston back out a little again, then opened the bleed screw and levered it back to where it just came from, and kept repeating that process. Little by little, it pushed back in a fraction further each time until eventually it was moving freely and I was able to fit the new pads.

As vgames33 said though, if it's taking all that effort then it might be time to fit some new parts.

[UncleBob]

if its rear disc brakes that you are doing, you are discribing a e-brake mechanism that complicates retracting the pistons. Need a special tool to do it (nothing all that fancy though, you can get one at any autopart store that sells or rents tools)

they are easy to recognise, the ebrake cable goes to the caliper. If it does, then its the screw type

Using a c-clamp is a good way to destroy calipers....should never take much force.

[MagicRat]

Originally Posted by UncleBob

if its rear disc brakes that you are doing, you are discribing a e-brake mechanism that complicates retracting the pistons. Need a special tool to do it (nothing all that fancy though, you can get one at any autopart store that sells or rents tools)

they are easy to recognise, the ebrake cable goes to the caliper. If it does, then its the screw type

Using a c-clamp is a good way to destroy calipers....should never take much force.

I agree, if its rear calipers, then that's your problem. Note, often, even if you use the special tool to screw in the piston, the caliper may leak. Rear calipers are susceptible to this problem much more than front ones.

If it's front calipers, get rebuilt ones. It should never take that much force, and if it does, your calipers are seized beyond all usefulness. Usually rebuilt front calipers are pretty cheap for domestic cars, often about $12-25 each.

Even if you are able to retract the piston using brute force, they will never work right and will drag and/or leak.

[bobss396]

When I push back a caliper piston, I pop the top off the master and leave it on but loose. If the pads were extended and someone topped off the fluid, you're also fighting against the fluid compressing in the master reservoir.

To push the pads back, I place the old pad over the piston and use a 4" C clamp, this allows it to push back evenly and not possibly cock the piston in the bore. If it gives me a fight, I either rebuild or buy a new caliper.

Bob