Uneven brake pad wear, now what?
 

My front right outside pad is completely worn. The inside pad still has lots of life to it. After reading this
thread, I think that I might have to lube the sliding caliper. How do I it and what piece do I lube?

I did notice on the outside pad that there was a real rough spot, the size of a penny, on the surface that touches the rotor. Would this be the cause of the premature wear?

Most brake pads use adhesive to make the actual pad stick to the backing. The "rough spot" is probably just the adhesive.

Mine was starting to do the same thing as yours, I just ended up replacing the calipers for $100 each instead of taking a chance with the brakes failing, i.e. if you have to ask what to do to fix a siezed caliper then you (and I) shouldn't be doing it, just for safety's sake.

That would be on the back side of the rotor. I'm talking about the actual surface that comes in contact with the rotor. There is a penny size section that flakes/crumbles away, right in the middle of the pad. It looke like it is in the exact location of where the piston comes in contact with the pad on the backside. There's an outline of the same thing where the other piston hits on the pad but theres not a rough patch though.

Look, if I can change my rotors and brake pads, I'm sure I can do this. I just need to know what exactly I'm lubing. Sheesh :rolleyes:

ck,
You want to keep the slider pins and the tubes the bottom bolts slide through greased. From what I've seen it's not unusual to suffer uneven wear with this "floating" design even though it's supposed to cure it. ;)
It sounds like possibly the metal backing plates may be missing if the piston shape is manifesting itself in the front side of the pad. My first problem was a stuck caliper caused by degraded rubber piston boots, locking the piston, preventing it from pulling back. This is easily spotted when the caliper is swung back off the pad mounting.

Glenn

Thanks! Now I wonder if using aftermarket (Raybestos) shims is part of the problem... They don't cover the entire backside of the pad. And looking at the SubaruParts.com parts diagram, they seem like they should. In fact, the OEM shims are doubled up on the inside (two on the inside and one on the outside). Diagram is here: SubaruParts.com brake diagram

I know my mechanic instructed me to reuse the OEM backing, and it makes some sense that the piston might exert uneven pressure on the pad if not backed in full. However, with 2 pistons is it only one doing that, and is it possible you're experiencing the stuck piston I described on one of the two?

Glenn

I don't think it's a stuck piston. I had to use a c-clamp on both to move them back out of the way to flip up the caliper. Would it be ok if I pressed on the brake while the caliper was flipped up and someone was watching the pistons? Or is there a possibility of pushing the pistons out too far if I were to do that (without having the pads to restrict their travel)?

Don't do that!
 

They will fly out if unrestricted. :eek: Mine were obviously shot, with metal showing through the piston boots and the boots were all brittle, etc. A visual would tell all. Be sure to load up the sliders with caliper grease, place the correct backing plates and should be good to go with the new pads. Be sure to bed them in properly too.

Glenn

I didn't know the importance of the caliper moving freely side-to-side. After really inspecting the booties and the pins that the caliper travels side-to-side on, I found that they were very dirty. They were stuck with crude inside the rubber booties. I took them off gingerly (the booties seem rather fragile) and cleaned all the metal surfaces and applied an ample amount of caliper lube.

I also installed new pads and new OEM shims (2 on the inside and 1 on the outside). My brakes work great now.

Sidenote: It's really amazing how something so little, and seemingly so inconsequencial as little rubber booties, could make such a difference in something so major like braking.