Rear caliper question Options

[mkernz22]

So I've noticed that my rear rotors look like they are barely getting used at all because of the amount of surface rust they keep on them. There is definitely some contact there because it never gets to too bad. The only thing is, this is on the outside of both rotors. The inside of both are so clean with no surface rust. Does anyone know why this would happen? Cause I'm pretty confused about it.

[Galcobar]

This suggests the caliper is not sliding correctly.

The piston of the caliper is mounted on the inner side of the rotor. If the caliper is in good working condition, then when the piston pushes against the rotor it also pulls the caliper backwards (law of physics, for every action there is an equal and opposite reaction). As the caliper moves backwards, it pulls the outer pad against the rotor.

If the caliper is frozen in place on the sliding bushings, then it won't move and will apply no pressure to the outside of the rotor, while all of the pressure is applied by the piston to the inside pad. If the caliper is partially seized, then the pressure will be unevenly distributed between the outer and inner pads.

So first thing to check is whether the caliper is sliding correctly on its bushings. If it's not, you can easily find new boots and bushings or whole rebuild kits online and in stores.

However, you might have a dual problem. If the caliper isn't properly cleaning the rotor, the rotor can develop pits (from rust) and ridges (from cementite, a harder-than-iron compound formed by overheated pad-rotor contact). Fixing the caliper won't get rid of the damage to the rotor; for that, you have to get the rotors turned and the damaged portions shaved off. If you don't, the pits will continue to exist and the cementite ridges will prevent proper pad contact, leading to the rotor staying rusty again.

This post has been edited by Galcobar: Nov 26, 2012 - 3:12 PM