How to free seized brake piston?

[Mjk]

While putting the finishing touches on what I consider a nice 1978 XS400 build, the front brake began giving me trouble and the piston is now firmly seized in the caliper assembly. The master cylinder is not the proximate issue (new HEL hoses and master cylinder rebuild kit), the piston is just stuck as could be by what appears to be a lot of rust.

Attempts to free the cylinder with vinegar, CLR, and light tapping/pulling with hand tools have been unsuccessful. Oddly enough though, in attempting to bleed the brakes to force it out, not much pressure built up in the system at all, even with what appeared to be all of the air out of the system, so something else MAY be at play.

I am at my wits end as to how to solve this seized piston problem. Any ideas, tips, tricks, or caliper assemblies for sale (that fit) will be tried to get the bike rolling again Thanks!

 

[BBS360]

Adapting a grease gun is a pretty common way to force the piston out.
Compressed air too, but turns it into a projectile.

Channel-lock pliers and elbow grease worked on mine.

 

[bmaster]

Mine didn't come out with greese or compressed air. (xs400 seca)
I needed some serious tools to seperate it from the caliper housing. I heated up the housing very much and tried to cool the piston from the inside (e.g. with water).
Then I used a pipe wrench to pull it out.

 

[Mjk]

Grease gun sounds and differential heating sound like the best options. Is it normal though for the brake lever to not gain any "feel" when bleeding a frozen piston? I would've thought it would still be able to build the pressure needed to feel like a normal brake. After I get the piston out (assuming that I do) what are my options in terms of actually re using the caliper and piston?

Thanks for being so quick to respond though!

 

[bmaster]

If your piston is stock in the caliper and you don't feel you're raising brake pressure. That could mean you have a leakage somewhere or you have some air in your brake hoses.

I only destroyed the piston. could be that there is some rust or waste in the caliper. i used some brake cleaner or WD40 together with scotch brite to clean it from the inside. The piston is replaced by a new one.

 

[Mjk]

I imagine it was air in the hoses because I didn't see or hear a leak, and the hoses and mc are brand new. That being said, paying for a new piston and rings isn't the worst thing that could happen.

I'm most interested in the grease gun option as it seems pretty straightforward. Do you have to use grease or would water or brake fluid work as well because they're all incompressible? I just don't want to have issues with little bits of grease gobbing up the whole system later on.

 

[kshansen]

I imagine it was air in the hoses because I didn't see or hear a leak, and the hoses and mc are brand new. That being said, paying for a new piston and rings isn't the worst thing that could happen.

I'm most interested in the grease gun option as it seems pretty straightforward. Do you have to use grease or would water or brake fluid work as well because they're all incompressible? I just don't want to have issues with little bits of grease gobbing up the whole system later on.

A new grease gun filled with brake fluid would be a good way to go. Biggest problem with using grease is making sure you clean everything completely as the oil in the grease is not good for the seas in the brake system. Water also might be a good option as long as you get everything clean and dry after it's apart.

 

[spectra]

I was able to get mine out today with a big set of channel locks like BBS360 said earlier. I was actually surprised how easy it was with a big set. Didn't even mess up the pistons either.

Hoping with a little elbow grease I can re use the pistons.........not as rusty as I thought.

 

[Mjk]

UPDATE: I went and bought a lever grease gun at menards. On my way home, my cousin said he simply freed the piston by twisting it out with channel lock pliers and some patience (which I do not have). Cleaned it up with some CLR and a scotch brite pad and bled it, the rubbers were all in good condition. On a test ride it stopped the bike very well.

Thanks for the help everyone!

 

[spectra]

Good to hear it al worked out for you!