Front brake not working properly, any suggestions?

My buddies front brake isn't working properly. It becomes stiff when it's pumped a few times, but then goes soft and doesn't work. This happened after a crash in a race. There is no leak, but after we took it apart one of the two cylinders that press the pad isn't pushing out when the lever is depressed. Any thoughts on what could be wrong?

One piston not working? Is that with no resistance on the piston/ pad as you where doing it? One piston working only means that the other one has more resistance and not an accurate indication of a problem. Sounds like air in line somewhere. Bleed the air out.

Agreed, sounds like air in there somewhere. Bleed it really well.

I would check the disc. If the disc is bent/warped it pushes the pads away from the disc and you will have to pump a couple of times to get the pads back in contact so they can work. Every time the disc turns it will cause the pads to be pushed away.

You might also check for a bent rotor. The brake can be pumped up while the bike is stopped. As it is moving the rotor spreads the pads apart too much due to it being bent.

Checking for a bent rotor as suggested would be a good place to start. A bent rotor can cause the pistons to be pushed back farther than necessary and increase the "free travel" in the system.

On the question of the sticking piston, push back the driven pad and place a screwdriver blade so that it blocks the piston that you say moves freely. Then see if the "stuck" one moves with a reasonable effort. If so, the fact that one is a little freer than the other shouldn't matter too much, since the pressure required to operate a disc brake is very high. If it seems too diffcult to move, you could have a damaged caliper, or corrosion in the bore.

Do be certain that the system is properly bled.

If it happened after a crash, you probably blew out/tore the seal on the master cylinder. Get a rebuild kit to fix it.

Thanks for all the tips. We're going to look at it this weekend and see what's up. I'm sure it's one of the problem you guys mentioned.


He might of distorted one the ends of the the hose (where the banjo bolt goes through). This would cause air to get into the line. I would buy new brass washers (4) and remove each end and check the hose ends, then replace the brass washers with new ones and rebleed the system ( it's probably due a fluid flush anyhow). Also, you can check the pistons on the caliper for pitting . I would start with the washers, fresh fluid and bleeding first. :cry:

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