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HELP! Can't get caliper piston back in!

Ok.. attempting to rebuild my '72 Aluminum S calipers.

I removed pads and pumped break pedal to try to get each piston about half way out. One piston (inside) moved out. The other did not. Fluid was leaking on the inside one (hence the rebuild). Maybe it went too far out so there is not a good seal to get the other one moving. Anyway, tried to push the inside piston back, but she won't budge. HELP!

What do i do? Tried using a block of wood and C-clamp, but not much working there.

Jeff
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Old 03-03-2004, 04:14 PM
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Can you get the caliper off and use compressed air instead of pumping the brakes? i just used a cheap 12v portable air compressor. mine acted quite similar.

seriously, watch your fingers. when that piston pops... it goes.
Old 03-03-2004, 04:23 PM
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problem is there is not a good seal. I would have thought that the c-clamp would have been the trick. Could the piston be physically stuck somehow?
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Old 03-03-2004, 04:26 PM
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I think you could do a search about this and get good results. Sometimes the piston isn't straight in the bore when you are trying to reinsert it. Reinreb is right, it's much better to take the caliper off and try to use compressed air. It's also easier to get the pistons to go into the bore straight with the caliper off the car. You should be able to use a C clamp to get it to go back in. Just adjust the position of the C clamp on the top of the piston as you try to compress it back in. When you get it back in, use the C clamp to hold it down while you ease the other one out with compressed air. You might use some channel locks on the top part of the piston to rotate it back & forth as you try to get it out. I like to put a block of wood (actually progressively smaller blocks) between the pistons as I ease them out with compressed air to keep them from popping out all of a sudden.
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Old 03-03-2004, 04:34 PM
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i suppose that the piston could be 'stuck' somehow, but there exists at some point a force that would 'unstick' it. I would think that Marvs sugestions of the channel locks would be a possibility if you can get a grip on them without damaging the smooth piston surface.

the other thing about using compressed air is that you can see whats going on when you pressurize it. when one of mine got 'stuck', i ended up poping the other all the way out. at this point i had to reinsert the loose piston back in so that i could get a seal on it and clamp it down. the stuck piston didn't have a good seal, but the air pressure built up faster than it could leak and the thing blew off like a rocket. i cleaned it up and reinserted it just enough to get a bit of a seal and then went to work on the other one.
Old 03-03-2004, 04:55 PM
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Put the assembly in the freezer for a couple of hours. If you can pack it in dry ice that would be even better, but a freezer will probably work. After a couple of hours, use a propane torch to heat the caliper quickly. then try moving the piston with the normal stuff.
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Old 03-03-2004, 05:28 PM
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Take the caliper off and do it with air. You may have a cocked piston. In which case, you will have to uncock it by pulling it back out (the one you pushed in).
Old 03-03-2004, 05:31 PM
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same exact thing happened to me, but when i inserted one piston in skewed. i was stuck. (hold the flaming) but i used an unapproved method. if you look at the piston there is a flange that the dust seal hooks onto. this doesnt go into the caliper, therefore you really cant damage it. use two large screwdrivers, vise the caliper down so it doesnt move and pry from two side. use the sections of the caliper that rides on either side of the rotor (raised section) for extra leverage. it will come out easy. so easy that you will wonder why you are messing with air. forget using the brake pedal to push them out. you are risking bending the hardlines. no way. sacrifice a bike pump, dude. hack the end off and hose clamp it to a bleeder and hold you finger over the open hole. stick a wire brush handle in between. you may need more wood. stir sticks from a paint shop i had lying around were perfect. one stick one handle equals the exact thickness of a rotor. jam that in and pump. pop pop. done. pm me if you need verbal instructions, i type like a kid. sucky. i will call you.
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Old 03-03-2004, 05:32 PM
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Sounds to me like the caliper is still on the car?

I assume this because you pumped the brakes to push the piston out?

Did you loosen/take the fill reservoir cap off before trying to push piston back in?

Scott
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Old 03-03-2004, 05:33 PM
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got it unstuck! Thanks for the help! it was cocked a bit, so a little adjusting with the c-clamp and all is well!

many thanks!!

Jeff
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Old 03-03-2004, 05:37 PM
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Old 03-03-2004, 05:37 PM
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