Brake piston

yellowdog

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Any tips please on how to get a stuck brake piston out .
I've managed to free one of the pistons and the other one has moved a bit but not enough to get a grip on to pull out so how can I get this one to move as the other one one moves freely ,I need to stop this one moving so that the stuck one can get the pressure on it ,very badly explained but that's me 😕
 

yellowdog

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Any tips please on how to get a stuck brake piston out .
I've managed to free one of the pistons and the other one has moved a bit but not enough to get a grip on to pull out so how can I get this one to move as the other one one moves freely ,I need to stop this one moving so that the stuck one can get the pressure on it ,very badly explained but that's me 😕
To add I'm using the brake lever to move the fluid .
 

5twins

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If you split the caliper in half, you'll find a cross-over hole at the top between the two halves. You need to block that off so cut a small square of aluminum from a beer can or something, place it over the hole, and bolt the caliper halves back together. Now you can blow compressed air in either side through the brake line hole or bleed nipple hole and it will be isolated and only blow that side's piston out.
 

yellowdog

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72 twin piston
If you split the caliper in half, you'll find a cross-over hole at the top between the two halves. You need to block that off so cut a small square of aluminum from a beer can or something, place it over the hole, and bolt the caliper halves back together. Now you can blow compressed air in either side through the brake line hole or bleed nipple hole and it will be isolated and only blow that side's piston out.
Thankyou ,sounds obvious now I'll give it a go tomorrow.
 

bosco659

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X2 for compressed air but when they’re really stuck I’ve used grease. Messier but more pressure. You’d need to make an adaptor fitting though. Brake line fitting with a grease nipple.
 

Paul Sutton

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I have used compressed air and you must be careful of the "gunshot" effect. The first time I did it was quite nasty, the second time I wrapped the caliper in a towel so nothing got loose. Careful not to scratch the pistons when you do the final and last bit of pulling out. I gripped the piston with vice grips but used a bit of aluminum so the jaws did not touch the piston surface.

Good luck tomorrow.
 

5twins

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If the piston only comes so far out and stops, you may have to "work" it. Press it back in with a big C-clamp, blow it out again, press it back in, blow it out, etc. Some penetrating oil around it's edges will help. Eventually it will come all the way out.
 

yellowdog

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Update ,doing what 5 twins said worked a treat ,both pistons out now ,I'm hoping I can reuse them as
they look in good condition to me ,the caliper is a bit manky though any suggestions as what to use to clean them up especially the inside around the seals .
Thanks everyone.
 

Paul Sutton

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With seals removed, I found the use of kitchen pot cleaning steel wool and plenty of oil cleaned all the crap out of the seal grooves. The steel wool packs into the grooves nicely to give full contact with the surfaces. I did not push too hard and hoped the oil would minimize an abrasion by the steel wool.

Note: I washed the soap out of the steel wool pads first.
 

gggGary

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For the bore itself, very fine sandpaper like 1000 grit and water. Try to work the whole bore evenly, don't just scrub away at bad spots.
For the seal grooves I like to take a piece of heavy solid copper wire, bend a 90 near the end, flatten square the end a bit with hammer/file.
 
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