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Discussion Starter #1
I am attempting to rebuild the callipers on my 1969 GT and I cannot get one of the pistons to compress more than about halfway. The other compressed easily with a channel lock, but not this one. So much so, it broke a brake compression tool I bought to try and get it down.

I am reusing the old pistons but cleaned them up nice and they look almost new. I generously lubed them with brake fluid but it made no difference.

Is it possible at some point they were warped imperceptibly and I have a lost cause on my hands?

Matt




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Have you removed the piston completely? Its probably an issue with the O ring seal getting twisted.

Also, undo the bleed nipple and see if that helps there may be a blockage somewhere.
 

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Discussion Starter #3
Have you removed the piston completely? Its probably an issue with the O ring seal getting twisted.

Also, undo the bleed nipple and see if that helps there may be a blockage somewhere.
Thanks for the feedback. I should have mentioned the Caliper is off the car and the piston was removed for cleaning. Prior to that I used compressed air to get it unstuck. New square cut seal and dust boot installed. I did have the bleed fitting in, it is a small matter to remove it and I will try it again.
 

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New ones are so inexpensive from OGTS it is not worth rebuilding the old ones and in addition if they were stuck then they have rust in the bores and they are not worth messing with anyway. Stopping is the most important thing there is!
 

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Discussion Starter #5
Following up on my original post. I took the callipers down to a local mechanic who likes a challenge and he got them working pretty easily. It seemed to all come down to technique, which my newbie self does not posses. To get the the piston out he carefully tapped the piston with a punch to make get absolutely level and plumb with the Caliper and then a quick blast of compressed air knocked it loose. After a cleanup with brake clean and a vigorous cleaning with a Scotch brite pad the new seals were ready to go in. He then placed the pistons in a vise, gently turned them in the barrel until they wouldn’t compress further and then used a flat bar on the face of the piston to fully compress them. This is the trick that Youtube can’t help you with, it takes quite a bit of feel to get right.


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After a cleanup with brake clean and a vigorous cleaning with a Scotch brite pad the new seals were ready to go in. He then placed the pistons in a vise, gently turned them in the barrel until they wouldn’t compress further and then used a flat bar on the face of the piston to fully compress them. This is the trick that Youtube can’t help you with, it takes quite a bit of feel to get right.
Brake fluid can be used as piston lube. I found some brake fluid compatible lubricate years ago that I use on the seals and pistons before re-assembly. If I can't squeeze the pistons in by hand, I usually haven't done something correctly.

Harold
 
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