Master cylinder??

[Fred1956]

I was at a race on Sun. riding the '04 EC300 & while whistling thru a rock garden section I tapped the rear brake and NOTHING!! Like the hose was cut into or the pin fell out. No resistance what so ever, after I unwound from the trees I plowed into, I hustled on down the trail for a couple of miles using front brake only & as I came to a nasty downhill section dreading the front brake only, I sneaked a try at the rear pedal & it was back! Worked great for the next 30 miles to the finish. I'm puzzled as to what could have happened. Do I need to rebuild master cylinder? Flush the system? Anybody else had this happen? Thanks

 

[lankydoug]

If there is no fluid loss it has to be Master cylinder. I've seen plenty of car MCs do it and a seal kit fixed every one unless the bore had rust pits.

 

[gasgasman]

Rock might have pushed the pads apart.

 

[lankydoug]

Rock might have pushed the pads apart.

Good point, then you have one or two strokes of the pedal before it back home.

 

[gasser]

Change the fluid it may just have a little moisture in it. Water in the fluid will boil when you heat the brakes up causing complete loss of stopping power untill the fluid cools enough to return the moisture(steam) to a fluid state. Once that happens full stopping power will be returned.

 

[Fred1956]

Thanks for the suggestions, I'll check those out

 

[jostby]

I agree with gasser. I think you boiled the brake fluid. If you change it make sure you use DOT4 it's rated for higher temps.
This has happened to me a couple times but not often. I'm usually able to find a creek to cool things down but the initial "find" is always a little scary. Once cooled off things work fine.

 

[cbutler]

Rock might have pushed the pads apart.

A rock or stick pushing on the side of the caliper and no breaks