1984 GPZ550 rear brake stuck

Finding a good master is proving challenging these days. When restoring my 750 I purchased something like three different masters on ebay (all badly pitted) before someone I knew offered one up to save the day. There are lots of generic units available that will work but you have to do some adaptation for the mounts. I've seen some different threads here so you may want to dig around in the archives and look for some photos.

I believe there are places that will re-sleeve motorcycle master cylinders, but I don't know how much they charge to do so. Ed

650ed wrote: I believe there are places that will re-sleeve motorcycle master cylinders, but I don't know how much they charge to do so. Ed

This process was mentioned in my post, “ to hone or not hone” I’m going to dig into this because it would be a great resource for us dealing with maste cylinder issues... if anyone has a source please post it...

Mikaw wrote: This is the tiny hole that allows pressure to be released and allows the caliper to back off a smidge and not drag

My master cylinder doesn't have that hole in it.

I removed the master cylinder and it was pretty disgusting so I cleaned it out thoroughly using brake fluid. There aren't any rebuild kits or even used master cylinders anywhere on the internet or CL so cleaning is the best I can do.

When I remounted the cylinder I made sure to spray down the lever components again with WD40 to make sure that they don't stick. I bled the brake and I found that the brake was still dragging. The lever rebounds fully and quickly, but the brake piston is still dragging on the rotor.

I removed the caliper, pushed the piston back in, then re-bled the brake to make sure it was okay. Again the brake was dragging.

I assume this means I need a caliper rebuild kit?

Bumping this cause I'm not sure what to do next.

The MC wasn't pitted but there were witness marks (to be expected). I'm just guessing that a caliper rebuild is in order, but I'm also not sure that I did things correctly with the MC.

I’d say by process of elimination that’s your next move... before you crack the seal on the piston or brake line, check the caliper mount bolts to make sure caliper slides freely on then. Might be a simple clean and grease to free up.