Ahhh my brakes!

[afrozenfyre]

I was taking a shortcut through some lonely residential city blocks yesterday which involved accelerating, and then braking for the stop signs pretty quickly. I did this for 6-7 blocks, moderate speed, medium hard braking and then WOOSH, brake lever goes straight to the bar and I keep moving. I hit the rear brake hard and ended up stopped in the middle of an intersection (as I said, lonely area luckily).

I was pretty freaked out, limped to a safe location and checked out the brake. Everything seemed ok, and after waiting for 10 minutes in the 95 degree heat, brake function returned and I (carefully) continued. Pretty disconcerting though, I'm just glad it wasn't an emergency situation.

I have an M750 with single disk, disc is pretty new, pads have <1000mi on them. Did I boil the fluid in the heat? Air in the line? Extreme brake fade? Brake function is normally pretty strong, and seemed to return to that. Line was bled about 3k miles/ 1 year ago (didn't ride much last year).

What should I do to avoid this happening again??!?

[DarkStaR]

Have you checked the fluid level in the reservoir?

[64duc]

  I doubt you boiled the brake fluid but it is possible. More likely is that there is some water (condensation) in the system. Flush with new fluid and bleed for air. Brake fluid, depending on which type you are using, boils in the neighborhood of 300 to 500 degrees, water of course at 212.

[afrozenfyre]

Have you checked the fluid level in the reservoir?

Yes, it was in the normal range, both during the issue and now.

  I doubt you boiled the brake fluid but it is possible. More likely is that there is some water (condensation) in the system. Flush with new fluid and bleed for air. Brake fluid, depending on which type you are using, boils in the neighborhood of 300 to 500 degrees, water of course at 212.

So you're saying the condensation could have boiled? Wouldn't there need to be a lot of water in the line to cause full failure and not just mushy brakes? Like, enough that normal brake function would be mushy?

[Howie]

The BIG reason for annual brake fluid change is water contamination.  When the water boils it you are dealing with water vapor creating bubbles in the brake fluid, which is quite compressible.  Do we know if that is what happened?  unfortunately no.

Carefully inspect the caliper and master for signs of external leakage.  If your bike has a rubber hose and it is over four years old, look for signs of ballooning and consider changing it.  There is a possibility the master bypassed fluid internally, but that will remain a mystery.  If you find nothing else, you might want to change it for peace of mind.  And, of course, renew the brake fluid with DOT 4 or 5.1.

[the_Journeyman]

I'm also going to go with the change for peace of mind.  I've got a single disc M750 and have NEVER had a problem with brakes fading like that suddenly.  I've been on plenty of rides, even 2-up where spirited riding led to heavy front brake use and they've only ever faded a tiny bit ~

JM

[BK_856er]

If the master cylinder is a question mark, the OE Brembo part is (usually) surprisingly inexpensive from yoyodyne.  Despite the goofy name, they are one of the 2-3 Brembo distributors in the USA.

BK