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Discussion Starter · #1 ·
Hey guys...

I have a couple sets of twin piston brake calipers that are in very nice condition but seized tighter than some of you tighten your valve cover bolts!



My question is if any of you experienced brake guys have any tricks to PREPARE the calipers for piston extraction before actually attempting. I have all the time in the world to either soak them, heat them, cool them....



I have tried compressed air (120psi) to no avail.



I have a good master cylinder and a short brake hose so I think my next attempt will be to rig the MC on a old handlebar, hook up the calipers, bleed the system and try pushing the pistons out with hydraulic pressure. Wondering if I could heat them with a heat gun high enough to really soften the seals before pumping would begin?
 

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Try using the hydraulic method like you said, that should work. The piston should move...you shouldn't need to soak it or anything with this method if you actually are getting pressure.
 

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Don't forget putting something between the caliper so if one decides to jump the gun it can be stopped and have the other catch up.
 

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Maybe you can use a C clamps, while the brake pads are still in , to push the piston slowly in,-- breaking the (seizure). Be sure to have the lid of the MC reservoir loosened, if this method is used,- so brake fluid has a path to least resistance.
 

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Discussion Starter · #6 ·
Maybe you can use a C clamps, while the brake pads are still in , to push the piston slowly in,-- breaking the (seizure). Be sure to have the lid of the MC reservoir loosened, if this method is used,- so brake fluid has a path to least resistance.


That, my friend, worked wonderfully. So simple I just ran out to the garage and did 2 calipers. They pushed right in...may be able to even save the seals for use again after a clean up. Now to just rig the master and have a go at them.
 

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I have never had any luck with even soaking them in the HOT sonic cleaner to loosen the seals. If there is ANY lip of the piston showing I have clamped on a pair of vicegrips and twisted back and forth while pulling at the same time. It's always worked for me. Just don't clamp it too far down the piston and leave nicks on it. At the very edge it won't matter. But it can be filed smooth afterward anyway.



The pumping pressure would be safer. But I would use a block of wood in there. Use a thick piece behind one of them until the other comes close to being out, then block that one with a thinner piece and push the other one out. Good luck.
 

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Discussion Starter · #8 ·
Oh, this is sweet....just popped out 10 seized pistons easy as pie.



All pistons removed with no plier scars, all but 2 of them just need a clean and polish.



Pushed them in with a c-clamp to break the seal...pumped them out with a good 1980 master-cylinder (clamped in my vice) and a short lower brake hose off a CB750F-SS. Didn't even need to bleed from one caliper to the next. Just hooked up and pumped em out. Nice when a plan comes together.



Messy tho.



Wis-CX
 

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I'm distracted by the avatar. I have nothing to say here. I had a sticky caliper, tried and tried, took the MC apart, checked the orifices piston, lever, finally I replaced my MC and the problem went away.

Rusty
 

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It would seem to me that most people should not use vice grips on their pistons because of the slight danger of distorting them slightly out of round. It's easy to put a lot of pressure on with the jaws of a vice grip. That might be O.K. for an experienced mechanic but many of us don't qualify. I've had no trouble popping out seized pistons with hydraulic pressure from the MC on my working bike. I now have an extra MC which I can use on the bench with the caliper in the vice and a two or three mm piece of sheet metal to stop the pistons just before they pop right out.
 
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