Front Brakes Locking up!!

[dtek01]

A few rides up and down the street the front brakes lock up as if there is too much pressure and will not release. If I crack a line the will un pressurize.

I changed the fluid and all and nothing. Can this be the master cylinder?

If so how do you rebuild one or take it apart to at least check for contamination??

Hitting the track tomorrow so I need to know asap Thanks!!

[trx310R#24]

calipers could be sticking... happen to mine :p

[DnB_racing]

Originally posted by trx310R#24
calipers could be sticking... happen to mine :p sometime worn pads will cause the piston to extend too far and cause sticking also... if pads are real worn it could be making this worse with all the residue build up

[dtek01]

Hmm. seems like it builds up pressure and the lever looses all freeplay and is way tight.

[Meat]

1. Unbolt caliper
2. Remove brake pads
3. Push pistons back into their bores with a C-clamp.
4. Pump brake lever.
5. Observe piston movements
6. Report back with your findings
7. Profit

[wilkin250r]

I've seen this same problem before, and I figured it was water in the brake fluid. The brake fluid itself boils at a REALLY high temperature, but water boils much lower. If you get too much water in your brake fluid, it doesn't even need to get hot enough to "boil", it just gets hot enough to expand. Once it expands, it puts pressure on the brake pads, which causes more friction, which causes more heat, which makes the fluid heat up even more and builds up more pressure, more friction, more heat, and even more pressure, ect ect.

Changing the fluid for me wasn't enough, still had the problem, I figure there was probably still traces of the old fluid. I needed to take apart the entire master cylinder and caliper and clean them and remove all traces of old brake fluid. I also sprayed carb cleaner through the brake lines (because carb cleaner will evaporate completely) to clean all the old fluid out of them. After I let them all dry and I put it all back together, it worked fine.

[dtek01]

Thanks guys. I will try all the above. It is my cousins bike with the problem not mine. He took apart al the calipers and all looked good. The pads are new.

We took apart the MC and checked all seals and for dirt contamination. Then bleed them as much as we could and it is much better but still builds up enough pressure to take all the slack out of the lever.

After the careful ride tomorrow we will completely flush it as you said and hopefuly that solves it. Really wierd problem for sure and just popped up out of the blue.

Thanks for all the help!!!!

[bigE28]

trx310#24 your pm box is full. i sent you a pm.