Front Brake locking up

[rndrkeagle]

I have a problem with my '04 -12R front brake locking up on me when I'm riding. I'm 95% sure that it's air in the system somewhere but I've bled the line all the way down (almost emptied the reservoir and added fresh brand new DOT4 fluid and bled about half that reservoir down too then topped off and closed it up). I'm thinking that the air might be in one of the pistons of the caliper. Anyone have any suggestions on how to get that air out short of completely rebuilding the caliper?
Is there something else I should be looking at? the lock up is progressive (starts out slowly applying more pressure until the wheel just won't move). I've never seen brakes do this but from the symptoms, I'm pretty sure it's air.

[1001yos]

A brake pad that has had brake fluid on it will lock up pretty quick. Also, if you take the caliper off while bleeding it and try a different position to work air to the bleed screw....

good luck!

Maybe try sanding the surface of the brake shoe itself. Careful, asbesos may be present.

[kajer]

a can of brake parts cleaner might help if it is the above problem??

[rndrkeagle]

thanks for the advice... I'm still pretty sure the problem is air (or something else) inside the system. The reason I say this is because when it locks up, simply opening up the bleeder valve releases the brake and I can ride again.

[kajer]

front brake locking up? How do you not go flying over the front end??? [confused]

[FIDOSOL]

Kajer, it's gradual, almost like the brake piston is being engaged by the front brake handle. Slow at first then harder and harder. Decent amount of time to react without dying.

[ophawk]

The best thing as suggested above is to remove the caliper, and also force the pistons back in until they seat forcing all the excess fluid/air/anything else out of the caliper. Then remount and flush the system with the new fluid. Seal it all up, then Clean everything with brake parts cleaner.

[Stevenc150]

it's gradual, almost like the brake piston is being engaged by the front brake handle. Slow at first then harder and harder.
Mine did this exact thing when I put on a Blast brake lever, to keep riding, until I got my Pazzos in. The profile was different. Did fine in the cool morning, but on the ride home when it was hot, she gradually locked up tight.

[rndrkeagle]

hey BPG.. can you hook me up with PN's and pricing on a front caliper rebuild kit? standard ZTL 6 piston caliper on my '04.

If I'm going to have to pull the entire caliper off.. I might as well rebuild it while I have it off..

[rndrkeagle]

so after bleeding it all out like I described above.. the problem is still there. I even went to the extent of trying to get the air out of the pistons by squeezing the lever and using a zip strip to hold it compressed, let it sit there for a few hours (hoping the air would float up toward the bleeder valve) and then releasing the bleeder valve later. No dice.. I'm going to have to tak the suggestion above of compressing the pistons back in to force the air and fluid back out of the caliper... the only problem I have is that the line doesn't have enough slack in it to get the caliper down far enough to clear the rotor... how do I get the caliper off without pulling the line off the caliper? (the book says to bleed it dry, pull the line and then the caliper but that would just introduce more air into the system) The guy at my local stealership parts counter said to pull the wheel off but that seems like a bit drastic... anyone have any better suggestions?

[the_F_inator]

I'm having EXACTLY the same problem on my 03-XB9 that I just bought... If you figure out what's up please do tell.

Off to go get another bottle of brake fluid & try some more stuff...

[rndrkeagle]

well... we figured it out... and it's not air in the lines... it was the replacement brake lever I got off of ebay... turns out that the portion of the lever that contacts and depresses the master cylinder piston, was about 1/32 of an inch too long. It was pushing the master cylinder piston in just enough that the relief valve wasn't able to open when the brakes were released. The fluid would heat up and expand and couldn't escape back through the master cylinder the way it was supposed to. We went to the extent of rebuilding the master cylinder, the caliper and flushing all new fluid through the system and when the problem was still there, we noticed this little tidbit in the service manual about the possibility of the master cylinder not coming all the way back out.

An easy test to see if this is the cause of your problem, is to remove your brake level all together and go for a short ride with just your rear brakes. (be very careful doing this of course).. Drive a few miles and see if the problem occurs. If not.. then your lever pin is probably too long.

Another way of knowing is to remove the pivot pin that holds the lever into the master cylinder/reservoir assembly and see how the pin contacts the master cylinder piston when you move the lever into position with the pivot "holes" lined up. It should just contact the piston but should not move it more than about 1/64 of an inch. (mine was pushing it in about 3/64)

It's all back together now but if I get a chance I'll shoot some pics of it and post them up here.

On a positive note though, when we did finally get it working, on the final test drive we took it out on, we passed Lance Armstrong out training in the hill country west of Austin. For a guy that retired 5+ years ago, he was hitting those hills with a vengeance.. he hasn't said yay or nay yet but I do hope he runs the Tour next year. (he's going to be in the Italian race... and will decide after that if he's going to run the Tour)

[Stevenc150]

well... we figured it out... and it's not air in the lines... it was the replacement brake lever I got off of ebay... turns out that the portion of the lever that contacts and depresses the master cylinder piston, was about 1/32 of an inch too long.
That is exactly what I was trying to say in my earlier post. You probably ended up buying the blast lever too. I just used a dremel and redressed the radius portion, worked great after that.