Rear brake

[bemusedinsojo]

Hello,
After a stint of riding on forest service roads my rear brake went out. I pushed the brake lever down but no stopping. After a harrowing descent slowing with gears and the front brake I made it to the pavement. Funny thing is it started working again, not like when air is in the system but normal operation and stopping. What could have caused this?

[ssevy]

Had this happen once on my mother-in-law's Buick. Sears replaced the master cylinder, but it still randomly occurred. Upon closer inspection, it turned out that one of her brake pads had actually broken loose from the metal mount, and was floating in place. Sometimes when the pedal was pressed, the pad had moved so it wasn't in place, and the pedal went to the floor. When the pedal was pushed again, the pad had shifted into place, and the brakes acted normal.
Not sure if it is possible for this to happen given the physical design of our calipers, but I would look to see?
Have also heard of some brake lines with a rubber lining having that strip off and temporarily plug the brake line, only to uncurl and then allow fluid to pass.
Were it my bike, I would flush and refill, and replace all the seals at both ends. If it's been awhile since you have flushed and replaced your fluid, you might have been dragging your right boot and overheated them, causing them to fade. This could happen if you were wearing a different pair of boots than normal, or doing types of roads that had you in a different riding position for extended periods of time.

[London_Phil]

Are the nuts at the bottom of the master cylinder rod, where it attaches to the clevis correctly adjusted, can get a situation where they back off, and there is too much play in the system ,so when you press down on the pedal, you are not fully operating the master cylinder, but that would probably not correct itself..
Brake fade is another possibility, although not so common in disc brakes.
If rear brake is dragging, you can get heat build up, causing all sorts of temporary braking issues.
Pipes can start to bulge too,

[Sin_Tiger]

If I we're a betting man my money would be on the master cylinder seals being gubbed. Not flexing back to a good seal when released.

[bemusedinsojo]

SSevy I was riding different roads and using the brake almost exclusively; I didn't want to skid the front on sand or gravel. So I may have faded it but I've never done it before and thought discs were immune. So there is that possibility. I'll look at a floating or broken pad tomorrow though this is not a Buick  LondonPhil, the clevis pin is secure but the nut is all the way down. Where should it be?
Sin, the fluid and system looks good but just in case I ordered a rear brake cylinder rebuild kit, although I see no leaking anywhere but in my old CJ5 the brakes went to the floor with no sign of leakage and the fix was to rebuild the master.

I also checked out the rear caliper for leaks; there are none. If the rear master fix doesn't fix then I'll rebuild the caliper. Bikebandit shows four seals for $40+. After searching the forum it seems 27mm seals from a Suzuki Hyabusa will work. Can anyone confirm this and know the year (we go by year not by vin).

Thanks for the replies. BTW photobucket really screwed the pooch. So much good info lost.

[Sin_Tiger]

Clean that master GOOD, there's a teeny weeny wee hole in there that's easily over looked  :icon_wink:

[bemusedinsojo]

Clean that master GOOD, there's a teeny weeny wee hole in there that's easily over looked  :icon_wink:

I'll stick a wee probe in the wee hole and push in and retract multiple times until we both...I mean until it's clean. In and out then back in....dang got distracted again. Ok will do.