Did My Brake Fluid Just Boil Or......?

[SPEEDKING]

Got a 2003 CR500AF and while on Singletrack a bit ago I came in hot on a corner and found my rear brake pedal WAY thru the stroke and NO brakes.

They came back but it has happened again. Is this just a brake fluid boil thing or do I need a Master Cylinder rebuild kit?

 

[mx547]

my experience with these problems has been this:

when i needed a master cylinder rebuild, i could pump the brake and it would work. when i boiled the fluid, the brakes wouldn't work again until they cooled. which is your case?

 

[SPEEDKING]

my experience with these problems has been this:

when i needed a master cylinder rebuild, i could pump the brake and it would work. when i boiled the fluid, the brakes wouldn't work again until they cooled. which is your case?

Pumping wouldn't do it, right through the stroke. I didn't realize that was the difference,,interesting. In fact I thought the brakes would fade when it boils and that was it.

Is there a better fluid I could use?

 

[mx547]

i've been told that the motul brake fluid was the best against boiling but i've never tried it.

 

[dirt bike dave]

Motul 600 is an excellent fluid.

If your brake pedal is a little too high, it is easy to drag the brakes, causing the fluid to boil.

Contaminated fluid has a lower boiling point than new fluid. Old fluid absorbs water from the atmosphere, lowering the boiling point.

When the fluid boils badly, you will lose all braking on that wheel. Basically, the hydraulic pressure generated by the master cylinder is compressing the bubbles, and not able to squeeze the slave cylinder and brake pads with any authority.