Rear brakes keep sticking

[jshultz78]

I keep having this problem over and over. I'll tear down the master cylinder, clean it out, reassemble everything, bleed the brakes, and everything will be fine, I'll have about 2" of travel on the brake pedal before they lock up, but if it sits up a while, if I barely touch the pedal the brakes will lock up and not completely unlock, I've already warped a rotor because of this. But if I tear it back down and re-do everything it'll be fine until it sits again. This time I noticed a very tiny hole in the same opening as the feed line from the reservoir, it was stopped up, so I cleaned it out with a strand of wire, they're working again now, but I got a feeling that it'll do it again next time I ride. Is there anything I'm overlooking? Is that 1/2mm hole a pressure relief or something?

Edit: I forgot to mention when the brakes were sticking, I couldn't even push in the caliper with a c-clamp until I removed the caliper line off of the master cylinder, so it's in the MC, not the caliper.

 

[frit91]

Is the piston getting caught up in the caliper, maybe getting offset to one side or the other or possibly just crooked or at an angle.

 

[jshultz78]

caliper is fine, it'll press back in if the line is disconnected from the MC. I think it was because of that stopped up pinhole, found another forum where a guy was having the same issues on a yamaha motorcycle, cleaned the hole out and it was working fine. Hopefully that's my problem. I get tired of cleaning the MC every time I ride it.

 

[alex456123]

Seized caliper/caliper pins?
Bad master cylinder?
Clogged up lines?
Idk just throwing out ideas

 

[cheese_05_70]

I had this same thing happen to me brakes sticking warped my rotor after I rebuilt my master cylinder. That pin hole is to bleed off the pressure that's on your rear caliper when you let off the brakes. Otherwise the pressure doesn't release and keeps building.

You can take master cylinder off and blow compressed air into the pressure side and see if air comes out where reservoir line attaches. If you get no air out its not fixed. I used a air nozzle with a rubber tip.I had to grind some off of my plunger ball where it fits into the socket. Wasn't letting it come down far enough to release pressure. I ground on the ball part. Hope this help