80 GS750E rear M/C

[Guest]

Have a problem with the rear master cylinder locking up when barely stepping on the lever, sometimes its fine, lately, rotor gets very hot, FAST!, my mech. says it might be the internal valve has some crud blocking the opening, rotor is fine, caliper were rebuilt a couple of years ago. things get hot and pads start to hang up, like an anchor. I want to replace the master but are new ones available or do I rebuild what I have, I would also like to replace the front master cyl./ lever complete with a separate reservoir as well. Tips on the rear m/c ?

[dorkburger]

I just fixed the same problem on my 1150. There was a small amount of corrosion on the steel piston that slides in the
m/c bore. I cleaned it up with a scotchbrite pad, cleaned the entire unit, and reinstalled. Luckily the seals were ok. All is good. Are you certain its the m/c and not the caliper?

Edit.....i just saw the caliper was rebuilt.......

[eil]

No need to get new master cylinders, just tear down, clean, and rebuild the ones you have with new OEM seals. I would tear down and inspect/clean the calipers at the same time just for good measure. There is a tiny pin-hole in each MC that allows fluid to return to the reservoir, make sure that's clear. If it's not, you get the symptoms you describe. Also upgrade to stainless steel brake lines if you haven't already.