86 250R no rear brakes - sometimes.

[Micahdogg]

I was riding the R around a very tight backyard track and I was on the back brakes quite a bit. After about 15 laps the rear lever just went straight down and I had nothing. Figured a brake line let go so I limped it over to the garage and let it sit. I didn't notice any fluid dripping, but after about 15 minutes I went over to check it and it was working again? WTF?

So I popped the reservoir and it was low. I added some fluid, little too much as the reservoir cap pushed some out. I even checked the bleeder and it shot out two good streams of fluid. Figured all was good, went back out and after about 15 laps the rear brake went to the floor again. WTF?

So I limp it to the garage - let it sit and now it has some drips from the swing arm skid plate. I can't tell if it's from the top of the reservoir where I overfilled it a little or from somwhere else though. But what would cause the brake to not work when it gets hot, but then it would come back when it cools down?!?!?

[leviblue]

pads... still have some on there? pistons sticking

[Micahdogg]

So as the brakes get hotter, the lines swell and piston has to move further out....then it gets stuck. Hmmm. Is this a theory or does it actually happen on these? I'll have to check the pad thickness when I get home.

[dougspcs]

Water in the brake system!!..it will settle to the lowest point(caliper) then as it gets hot it boils to vapour and as we all know air causes spongy brake pedal. It cools and turns back to liquid, pedal comes back!!

Drain and flush the entire system with clean fluid..also clean any brake fluid up when you are done. It eats paint!!

25 year old brake fluid is sure to have condensation in it!!!