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Re: update Posted by Ari [Email]  (#2847) [Profile/Gallery]
(more from Ari) on Fri, 21 Aug 2009 00:42:06
In Reply to: update, Erik919kt, Thu, 20 Aug 2009 09:41:51 Members do not see ads below this line. - Help Keep This Site Online - Signup |
The caliper is designed to slide - that is how it centers itself. It sounds like it's not sliding properly. It could also be a binding caliper, but usually binding occurs when the pistons won't retract - you can usually get plenty of force to expand it (putting on the brakes).
I'd pull the brake caliper back off. Make sure the two long, shiny bolts - the ones with the allen sockets - are clean and shiny. I usually wipe them down with some alcohol, and after they dry, a thin wipe of high temperature grease. They are shoulder bolts, so they should screw in easily, and then suddenly stop (when you hit the shoulder). If they went in cocked, there could be binding.
When you take the caliper off, have someone press the brake a little, just to make sure you see the piston push out. Hold the caliper about where it would be normally when you do this. If it doesn't push out, it could be a bad piston, or you might have kinked the brake line. If it pushes out, use a C-clamp or big pliers to push the piston back in. It should go back in.
If the piston doesn't come out or go back in, it could be a bad piston or a kink in the brake line. If the brake line got bent, it can damage the rubber internal hose. You can get a constriction, and that will limit the brake pressure. Usually this doesn't keep the piston from going out, as you get LOTS of pressure. But it can keep the piston from going back. When you take your foot off the brake, the pressure is relieved. The piston won't retract by itself, but minor imperfections in the rotor can push it back to where the pad no longer rubs. A problem internal to the hose can cause what is essentially a one-way valve, trapping the pressure on the piston side. This makes it hard for the piston to retract, and the brake pad binds.
To tell if this is the problem, crack open the bleed nipple a little. No fluid should come out. Have someone gently press the brake just a little - fluid will come out (be prepared to catch it!) If you get fluid coming out when the pedal isn't being pressed, or get no fluid when the pedal is pressed, suspect the brake line was damaged.
If the brake line seems OK, and the piston won't extend or retract properly, replace the caliper. But before that, I'd make sure the sliding bolts were clean, greased, and aligned right, and reinstall the caliper. With the wheel off, have someone press the brake pedal (the car can be off, they'll just have to push a bit harder). See if the piston pushes out and the caliper self-aligns. See that it relaxes a bit when the brake pedal is released. Ideally, jack up the front end of the car so both front wheels are off the ground. With the car out of gear, you can turn the hub to see if it binds (it will be hard, because you're turning part of the tranny internals and the other wheel). Even with the additional drag, you should be able to tell if the brakes are still binding.
posted by 192.249.47...
, Fri, 21 Aug 2009 00:42:06 <-- Viewing This Message
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