[marlopez]

edit: ok the former problem is fixed. i have normal stopping power. but now what happens if i sit for a while the tension or how far the lever can be pulled is normal. but if i start to brake, the lever goes farther and farther back, so i have to pull it more to get equal stopping power.
what causes this?
first, i am almost sure that there are no bubbles in the brake lines. could there be a leak in my system?


i have shimano xt hydraulics and i rebled my brakes, and my rear brake doesnt seem to bite. i have to pull the lever so hard for it to lock, there is no modulation at all. they used to work great.
at first i thought that maybe there was just fluid on the pads or rotors so i cleaned them and baked the pads. and i rebled it and made sure there was absolutely no bubbles. but nothing helped.

but what im wondering the problem may be is that when i bled them someone told me to take the pads out and i always bleed w/ the pads in but i just wanted to try this. so as i was pulling the lever to get the fluid to go down i wasnt paying attention and one of the pistons got over extended and the fluid started to pour out from behind the piston. i didnt realize this happened until i noticed a huge puddle of fluid. so could something have gotten unattached?

 

[Brian HCM#1]

Toss the pads and then rebleed the system, sounds like there maybe air in the system.

 

[marlopez]

why toss the pads?

even if there was oil on the pad wouldnt baking it dissolve the oil away?

 

[sub6]

Originally posted by marlopez


even if there was oil on the pad wouldnt baking it dissolve the oil away?

Well, no.

XT's use mineral oil; my understanding is that the way to get mineral oil out of pads is to boil them; baking doesn't do it.

Try that. If it doesn't work get new pads.

If the pads actually move to squeeze the rotor, and you don't get any braking power, that is because the pads are contaminated, there is no other cause.

Be sure to clean the rotor thoroughly (and the rest of the caliper while you're at it), and be sure to check to see if you have a leaky seal around whichever piston popped out. That could lead to a continuous contamination of the pads/rotor.

 

[marlopez]

ok so i rebled it and there lots of bubbles. then i rode it around and brake still sucked. so i baked the pads, then boiled them and i cleaned my rotor and caliper. it still doesnt brake as hard as the front. so ill give it a couple days and see how its goes.

next ill check the leaky seal thing

 

[marlopez]

Originally posted by sub6
be sure to check to see if you have a leaky seal around whichever piston popped out. That could lead to a continuous contamination of the pads/rotor.

how would i be able to check that? from the lookes of it it looked fine.
the former problem is fixed. i have normal stopping power now. but now what happens if i sit for a while the tension or how far the lever can be pulled is normal. but if i start to brake, the lever goes farther and farther back, so i have to pull it more to get equal stopping power.
what causes this?
first, i am almost sure that there is no air in the brake lines. could there be a leak in my system?

 

[sub6]

It's -possible- that there's a leak in your system, but what you're describing sounds like you're just low on brake fluid. Did you fill it up so that the reservoir is overflowing - no air in the resi at all?

If it's not that, you could have either a leaky piston seal or a leaky connection at either end of the hose, it may be getting past the compression fitting.

You'll know if you have a leaky piston seal if you see brake fluid dripping out of the caliper when it's not supposed to be.....

 

[Repack]

If you have a leak, as fluid goes out, air will be coming in, producing bubbles. If you have never dealt with this sort of problem, you are learning the hard way like I did. The really s***y part about it is that it is possible to have a leak, but not see it. Most good brake lines have 3 parts- the outer sleeve for protection, a layer of some sort of insulation, and then the inner sealed tube. It is possible to rupture the inner tube and have no visible damage. It doesn't take much air in the system to kill a brake. And it may not happen suddenly. I have seen damaged lines hold up for many dh runs before they burst. Are there any kinks in the line?

Alcohol also works well to clean the pads. Just let them soak for a while.

 

[marlopez]

i dont think i have a rupture in the line because my brakes were working perfectly fine until i rebled them and my piston came out.
the reason i dont think i have a leaky piston seal is that there is barely any dust around on my caliper, and where there is its not anywhere near the piston that came out. and i went to a really dusty place yesterday.

but i definitely know that i am low on oil somehow. this is annoying