yz400f rear brake issue *urgent*

Well planned to go riding today :thumbsup: , then had some issues with oil leaking from my frame. after repairing that we noticed the rear brake was not working. Pumped it, put new fluid in it, took the rear wheel off messed around with the pads, etc but nothing. :thumbsup:

Everything we tried, we could NOT get the rear brake to work. The rear brake piston would move a little bit in and out when we pumped it with the pedal, but very slightly. It seems like the piston isn't coming out far enough to make the pads squeeze against the brake rotor.. Planned to ride tomorrow and I would like to be able to use the rear brake because i DO use it quite often :confused:. Any suggestions?

help is appreciated

Did you try bleeding it?

How much slack is there in the pedal? Sometimes after removing the tire, you may need to retighten that.

Check the brake pad pins for wear grooves or notching.

I don't think there's any slack in the pedal and the pads are in relatively good shape. I replaced them last year and only had about 5 rides on them before winter came. None of these issues were present when I put the pads on last year either :thumbsup:

my buddies yz 250's rear brake just quit a few months ago. we tried bleeding it, checked pads, pins, leaks, anything we could think of on the trail, but when we got back to the trucks and put fresh brake fluid in, voila, worked great. the fluid had been heated up so many times that it just turned to garbage.

I've seen brake fluid come out and look kike it had been cooked. That may be your problem

We put new fluid in a number of times.. it didn't help :thumbsup:

maybe it's time for a rebuild of the master cylinder or the caliper :thumbsup:

maybe it's time for a rebuild of the master cylinder or the caliper :thumbsup:

I don't see how it could've ended up needing a rebuild because of sitting all winter. The brakes worked fine all last season

Try searching the thumpertalk archives for something(I would but I am Horrible at searching for info). Also to add on to what everyone else check for dirt or grit in places that could be locking things up. If you can't fix it for tommorow then use compression braking. Other than that I can't help you without seeing it.

Like the other guys said, why don't you try rebuilding it? It's not that hard and if you take everything apart carefully you may be able to reuse the rubbers. From sitting for a while the brake fluid could have deteriorated whatever seal or part that was probably going out before. Brake fluid is the most corrosive fluid on a bike and will eat through things eventually. Got Manual?

You could always try the rear brake with the front master cylinder. hehe Or try to really explain whats going on. What you feel and what works what doesn't.

We tried more than one master cylinder, and the problem was the same

then you've narrowed it down to the calipers...time for a rebuild, sounds like.

remember all it takes is one seal and you loose all of your pressure. A master cylinder in a car can go out in one instant, thus there is an E-brake directly linked to the rear brake system

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