I had an interesting experience over the weekend. While traveling in the Virginia mountains, off of the Blue Grass Trail. While traveling down a treacherous switchback my rear brake pedal sunk to the floorboard. I was able to pump it up part way but it just went back down again. I reverted to transmission braking and some front brakes for the next mile or so.

When I was able to stop at a level spot I got off the bike and expected to see brake fluid all over. The bike was dry??? I then pressed the pedal and it pumped back up to its normal level - WTF? I continued home (200+ miles) with no more issues at all.

Does anybody have ANY ideas what would cause this?

 

Sounds like you used too much rear brake and boiled the fluid. Try using the front brakes more, that's where 75% of your braking power is.

 

DOT 4 you have to drain and refill every two years or you will have moisture in your brake fluid,thus the boiling will occur when hot.DOT 5 only when dirty.

 

I tend to agree with these guys, you probably used way too much rear brake. You should also pump the brakes in cases like these to keep them cooler. Long, continuous braking is usually the problem. Don't know if they still do it, but on Pike's Peak they had a checkpoint on the way down, they checked your brakes and if they were too hot, they parked you to the side until they approved your return to the road. I've done that trip several times, the first few I sat. Learning more about pumping the brakes and serious engine braking I didn't have to stop the last couple times.

 

Yup - I did that during a RLAP class - too much rear brake, for too long, and it boils. Let it cool down, and it's fine.

Carried that lesson to the mountains for my road trip last month - engine braking for prolonged descents is a good thing.

Matt