Rear Brake Overheating

I'm having a problem with the rear brake overheating on a 99 WR400. After riding in tight down hill stuff and dragging the rear brake for a while it starts to squeal and then I lose it completely. I replaced the pads with stock pads and put new DOT 4 fluid in while bleeding out the old stuff. Even after this it still overheats. Any ideas what could be happening and how to fix it? :)

Sounds like the caliper is not releasing properly after you are letting off the brake. 1st check to ensure that your lever is not binding and has a slight amount of free play when released. If this is ok then you should closly inspect the seals on the caliper. it is possible that some dirt has worked it's way between the seal and the side wall of the piston that is just big enough to cause some binding when the brake is released.

Another item, check the brake pin. Remove it, if it's gouged or scored badly, replace it. You can steel-wool or scotchbrite this part to clean it up. Put some high temp grease on the part.

Also, go ahead and remove the pads again--take solvent and a toothbroth around the piston/seal area. Could be some gunk in there stopping (and guaging) the piston.

Good luck

Kerry.

If you replace your brake pin, get an updated stainless unit from one of the aftermarket places like Moose, Thumper Racing or whomever. It will out perform and last longer than a stocker.

I always use a quick-dry graphite spray on my '99 brake pin. I'd use grease, but I'm paranoid of it getting on my brake pads somehow, especially when I'm relying on them as a life support device in an extreme downhill situation. My pins are still the original stockers and have not developed any grooves to date using the graphite spray.

Remember, Yamaha has no concept of what grease or lube of any kind is. I've seen F&R axles and steering stem bearings cold weld themselves to whatever part happens to be nearby.

Hope this helps...

The brake pin did have a big groove scraped in it were it holds the pads. When I put it back together I tried to put the groove on the bottom. I didn't have time to replace this yet but I will before next ride. Wonder how this pin gets worn so quickly? Should I check the front pin also?

Check the disk rotor for any warping, this can eat the pins off the caliper on non floating disk rotors.

Boiling brake fluid is most likely the cause. The caliper gets really hot and boild the fluid, causing bubbles in the fluid system. Bubbles are the enemy. I see this a lot in desert racing when dragging the rear brake over miles of whoops and such.

As for a cure???

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Pretend it's flat and give it the gas.

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