While decending a steep grade and riding the "twisties" the rear brake pedal suddely went all the way to the floorboard. I had absoulutly no rear brakes! I was able to finish the ride using only the front brake and motor compression. Within 5 minutes of stopping for a drink of water, the pedal came back and I had solid rear brakes. I have checked for leaks, and found none. Checked the fluid level and all was well. Checked the pads and had plenty left. So, I am stumped! Outside air temp was about 95 degrees and elevation about 3000 feet. If anyone has an idea, I would appreciate your thoughts. Thanks in advance!

 

Come on guys and Gals, Is there no one who has experienced this issue? I would think the brain trust here would at least have some ideas! Appreciate any help. Thanks!

 

Same thing happened to me while riding a Sportster in Colorado a few years ago. 70 mph down a mountain in heavy traffic went for the rear brakes and they weren't there. Took it to a dealer in the area as it was under warranty and they said air in the lines. They bled them and I was good to go for the rest of the trip.

They said it happened all the time when people bring bikes out there into the mountains from lower elevations.

My pedal never came back all the way like yours did though. Might be worth the time spent bleeding them to be sure.

 

Could have been the the caliper/disc got very hot and created brake fade.
Vehicle braking system fade, or brake fade is the reduction in stopping power that can occur after repeated application of the brakes, especially in high load or high speed conditions. Brake fade can be a factor in any vehicle that utilizes a friction braking system including automobiles, trucks, motorcycles, airplanes, and even bicycles.

Brake fade is caused by a buildup of heat in the braking surfaces and the subsequent changes and reactions in the brake system components and can be experienced with both drum brakes and disc brakes. Loss of stopping power, or fade, can be caused by friction fade, mechanical fade, or fluid fade. Brake fade can be significantly reduced by appropriate equipment and materials design and selection.

Brake fade occurs most often during high performance driving or when going down a long, steep hill. Owing to their configuration this is more prevalent in drum brakes. Disk brakes are much more resistant to brake fade and have come to be a standard feature in front brakes for most vehicles.

 

Would it allow the pedal to go to the floor when fading? Just curious, when the brake fluid viscosity decreases due to excessive heat would it allow it to compress more, thus allowing to pedal to drop more due to increased piston travel in the master cylinder?

Or would it be the perception that the pedal travels further because you're pressing harder and harder on the pedal trying to get a reaction from the braking system?

Probably thinking into it too much on my part but I'm working through an issue with my rear brakes right now...

 

Yeah, I agree. Your rear brake rotor got so hot that it heated up the caliper which heated up the brake fluid and actually boiled some of the fluid. That's where the air comes in. When you applied the brakes, you just compressed air and very little fluid. You need to at least bleed the brakes and, better yet, replace the fluid in the rear brakes.

The same thing happened to me once and it blued my rear disc.

 

Bled mine today and that did the trick.

 

Thats why Dot4 brake fluid needs replaced every 2 years. as little as little as 2% moisture can lower the boiling point drastically,causing pedal fade. Riding down a mountain is easy to warp rotors, using a low gear so that you don't ride the brake is important. Mike

 

That's one way to avoid the problem, drop down to a lower gear to begin with.