Question about rear brake pad bed-in, possibly binding?
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Question about rear brake pad bed-in, possibly binding?
Yesterday I changed the rear brake pads, and tonight I noticed after a freeway drive that one rear wheel is hotter than the other. You can see and feel that the disc is hotter too. Looks to me like a pad isnt freeing off totally, is this something that happens during bed-in or should I worry?
I'm pretty sure I put it together right, caliper slides freely, etc. I even added some grease to the 2 slides.
I'm pretty sure I put it together right, caliper slides freely, etc. I even added some grease to the 2 slides.
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Joined: Aug 2002
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From: Warwickshire
It sounds like you did not back the piston off quite enough. It needs about .....
.5mm or .012" clearance to allow the pads to be knocked back away from the disc surface. The discs have a run out of around .005" to .010" to push the pad back after each application of the brakes. If there is not enough clearance the pads will drag continuously and the whole caliper assembly will heat up then eventually bind.
Tech Guru
Joined: Mar 2003
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I had a much worse, similar situation....
... it turned out that the pads went a bit crooked upon the first brake application. Taking it all apart, aligning it, lubing the slides, adn re-assembling fixed it. In my case it was so bad the parking brake hardly worked. Do that test.
Grant
Grant
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From: Warwickshire
If you wind the piston fully back into the caliper, then fit it without adjusting....
it to give the correct clearance, there is nothing holding the pad straight against the face of the disc so it could twist as the disc turns then jamb as the brake is applied, this would cause the edge of the friction surface to be worn off as we have seen on couple of photo's now.
AudiWorld Super User
Joined: Dec 2003
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From: Gardnerville, NV
Nor true, Edd! Apparently you don't understand the piston retraction mechanism...
It is built into the caliper designand is independent of rotor run out. A worn in rotor on a zero clearance wheel bearing will run dead true, why old rotors are better than new. It is the piston seal that retracts the piston when hydraulic pressure is removed. The O-ring is deformed under hydraulic pressure and it returns to its original CS when released, moving the piston back just enough.
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