Rear Brake Trouble HELP!

[GTiR_pilot]

Hi i URGENTLY need help to try to fix the rear brake on my 2007 Yamaha YZ250F. My problem is that when i lightly pump the rear brake lever (only pushing it to halfway through the stroke) the pressure inside the brake lines builds up, effectively dragging the rear disc. Sometimes to the point of a complete grab when you pump it 3 or 4 times. But when you press down hard on the lever it will brake normally and release normally but when you go to apply the brakes again there is no pressure at all on the lever until you pump it lightly again. I have a very important race i need to attend on the 29th so don't have very much time to get this sorted as parts shops will be closed during xmas and i'm stumped to what the cause of this problem may be. Any help will be HUGELY appreciated.

 

[BLACKeR]

have you tried bleeding the brake line?

 

[whenfoxforks-ruled]

Check your pads and bleed. Push the piston all the way back. This is a good thing to do when you wash. Then pump your brake pedal and see if the piston is hanging in the caliper. It takes some pretty good pressure to move the piston all the way back in. But you should be able to do it with your hands. If the pads are really worn funny things can happen. If you are dragging the rear brake it can overheat the brake and cause problems also.

 

[GTiR_pilot]

Yes i have tried bleeding the line but it doesn't seem to be helping. There are no oil leaks anywhere and i have tried pushing the piston in the caliper and it seems fine aswell. The brake pads aren't very worn either (well at least i don't think they are, they still have about 5mm of pad left on each one)

 

[mideastrider]

Check your brake petal and make sure its working freely and not binding in anyway. I wonder if its coming all the way back to the top (up) everytime you use it. My sure the return spring is in good shape. When lightly pressing brake petal it may not be returning all the way but when pressed hard it may load the spring enough to completely return to the top. Just something to look at.

 

[GTiR_pilot]

Thanks for your help guys, Fortunately i think i was able to diagnose the problem. I took the caliper end of the brake line off the caliper and pumped the brake. There seemed to be sufficient pressure to push the piston against the pad. So i connected it back to the caliper and pumped the brake. Still same problem with binding to the disc. As soon as i loosened the bolt connecting the brake line to the caliper a whole heap of pressure released and the brakes became unstuck. So thinking that maybe something was preventing the oil returning through the brake line, I took the whole brake line off and reversed it so that the end that normally connects to the caliper was at the master cylinder end and vice versa. I started pumping the brake and there was no pressure build up to close the pads on the disc. So my theory is theres some sort of gunk or tear in the brake line thats acting as some sort of one way valve. If anyone disagrees or thinks it might be something else, please share your ideas.

 

[mideastrider]

You could be on to something, I never had it happen on a motorcycle but I did have a front brake line on the suburban close up. It was both front wheels actually. Turns out one these fast oil change places put transmission fluid in the master cylinder. The brakes would work fine for 2 or 3 stops then they would just start locking up, eventually coming to complete stop.

 

[whenfoxforks-ruled]

Upgrade to some stainless braided lines. Oem brake lines can get soft spots in them. The soft spot is easier to expand than the caliper. Some stainless will give you back the solid feel and then some!

 

[GTiR_pilot]

Kool dude thanks for the tip.

 

[Rotorranch]

It's an '07 bike, so I wouldn't think the line has deteriorated that quickly.

It really sounds like the link from the pedal to the master cylinder is adjusted wrong, not letting the master release the pressure.

Just a guess.

Rotor

 

[IndyMX]

Or that brake line could have just been defective.

 

[GTiR_pilot]

Yep, i replaced the brake hose and now is working completely fine. So obviously had a defective brake hose.