sticky rear brake

[stroberts22]

I rebuilt the rear master cylinder and brake caliper on a 82 R and the thing starts sticking after riding it. I have to keep a 8mm with me to bleed off pressure. I saw the Chameleon Tecate having the same problem last year at Trikefest. He would run down the strip and have to come back and bleed the caliper off like I'm doing after each race. I have made sure the pins are free and greased so there is no binding of the caliper and the pedal has free play in it so the master cylinder is not pushed. What could be causing it to build up pressure?

[Daddio]

Hartley, 1upfront, had that same exact problem on one of his 250r's. There is an extremely small hole in the master cylinder that the fluid returns to the res through. If it is just partially blocked, not all of the pressure is let off of the caliper, so the brakes drag a little and it gets hot. Then when the fluid gets hot it expands and causes even more pressure to develop inside of the caliper and your brakes end up locking up.

[manbearpig]

must be in the air right now. im replacing one of my master cylinders that had this exact same problem. this one started sticking, i pulled it apart, cleaned it and put it back together. was fine for one race then it started leaking, and because the tiny passage was blocked it drained the fluid from the cylinder past the seal an the piston ended up sticking. no fun, but luckily i have a replacement. i have another if you need shannon

[El Camexican]

As said above, your brake system needs to be able to bleed off pressure as the heat builds up. There are two possible causes to your problem. One is that the piston is adjusted too far into the bore and is not returning far enough to allow the heated fluid to return into the reservoir. The second is that the reservoir vent hole is plugged. I don’t know your ride, but this is pretty standard advice.

Pull the reservoir cover and carefully pry the pads apart in the caliper with a pry-bar. You should see the fluid level rise in the reservoir. If it doesn’t, or you can't pry teh pads apart the piston adjustment is your problem. Even if it does rise freely during the test back off the adjuster a bit as it may change when hot. Next remove the rubber in the filler cap and look for a little hole in the cap, make sure it is clean and unobstructed.

The only other cause of a problem like yours that I’ve seen (once) besides what I said above is a separated inner brake hose that would seal up after the brake was applied and stay locked after the brake was applied.

[stroberts22]

Thanks ya'll for the help! I will pull the master cylinder back apart and check everything ya'll said.