1978 KZ1000 A2A rear brake question

What's going on is my rear brakes seem to stick in an "applied" position after the bike gets hot. What I've found is that after using the rear brake a few times it will get so bound up that I can't roll the bike in neutral and can easily feel the brake when shifting from one gear to another or rolling to a stop. They get hot enough to smoke.

I've tried to use channel-lock pliers to compress the shoes off of the rotor with marginal success. The only fix I've found is a number 10 metric on the caliper bleed valve to release the pressure. I have examined the two pistons in the calipers and they have some galling/lost chrome. I originally thought that was the problem, i.e., the pistons are sticking in a closed position, but I don't understand why brake fluid is released from the bleed valve when I open it when the brakes are stuck.

Could the problem be with the rear master cylinder sticking in an applied position or is it more likely the caliper pistons are the problem?

Any suggestions from experience would be appreciated. Also, your suggestions on a good place for parts would help since the rear pistons seem to be getting very scarce.

Thanks,

When is the last time you changed the brake fluid?

Changed it when I went through the whole remove/replace process for the rear calipers and pistons trying to figure out WTF. About 2 months ago.

2centwurf

Sorry; that blows my theory that there might be some thick funky stuff lurking in the system. Ed

Thanks for the reply. I just hate to fall into the parts-changer mode when parts are hard to find and expensive.

My understanding is that there is a small orifice in the master cylinder that serves as a pressure release when the brake pedal is released. Could that be clogged? (sorry, but just grasping at straws here). Ed

First I've heard of it, Ed. I'll give that a search and look. You know after 34 years something could get clogged.

When fully cooled, would re-adjust the push rod from the brake pedal to the master cylinder, to allow more clearance before it contacts the master cylinder.

This means the pedal will be pressed marginally further before the m-c piston begins moving.

When adjusted too closely, the heated fluid expands to begin activating the m-c piston, whereby the brake locking gets progressively worse, until the disc becomes sizzling hot and locked tight.

If allowed to cool, the locked brake should release, but will again lock up, unless the push rod is adjusted to allow more slack.

Good Fortune!

I had the same issue on my goldwing front brake. had the calipers apart no less than 6 times flushed the master cylinder twice and cleaned vent marginal success. it seems my pads were wore and 1 piston would push out too far and stick. Havent had the problem since the new pads.

(clening the vent seemed to help when i was chasing the problem but quickly returned)

seemed it was worse when i didnt ride the bike everyday i would break the bleeder loose and would be fine for a few days then would return few miles into a ride

Try this website for brake parts:
www.partsnmore.com/parts/kawasaki/kz1100b/?filters [category]=chassis

Check your mastercylinder also to make sure its not hanging up