rra640

I did a search and didn't find anything similar.

I noticed that my left rear brake rotor has multiple large ridges across the surface. They are fairly deep. The rest of the rotors are very smooth. What could have caused this? Pads are fairly new and rotors have never been turned, but appear to be in good shape.

I was going to pull it off and have it turned, but would like to know what the root cause might be. Would it be better to resurface both the left and right at the same time? The right side is very smooth. I thought maybe some of the other components within the caliper might need to be replaced??

I am not getting any type of vibration, noise, or squeaking. Handling is fine. Just replaced the OEM tires and wear was even on the original tires.

Vehicle is a ’98 GS400 46k miles. All stock.

Thanks!

rominl

iTrader: (4)

umm, some stones or so got caught between the pads and the rotors? just a guess

rra640

Well, I guess that's possible... but I would be surprised if that were the cause. The ridges are very smooth, kind of rounded over. Not sharp.

I'm not even sure it can be turned because they would have to take a lot off to get smooth.

I'm just afraid that if I replace it I would chew up another one if I don't know what the cause it. Is it wise to replace both sides at the same time or can I just replace the one that is bad?

BossGS4

iTrader: (2)

I've seen this before on a single piston Subaru caliper. For some reason the piston got 'hung up' on one side. As you kept using the brake the brake pad started to wear unevenly, so even if the piston 'un-sticks' the pad is already wearing at an angle. This wears the pad faster and eventually the steel backing plate starts to grind your rotor and PRESTO gauging occurs.

Agressive pads can also cause this, I want to say Metal Master pads used to rip up my stock Mitsu rotors or was it Hawk.

Either way I would examine the rear caliper piston and get new slotted rotors and ceramic pads.

DaveC

rra640

So, if I understand you correctly... you are saying that it might have been stuck at one time and is now "unstuck"? I'll inspect them and see if the wear looks uneven. I have never noticed any metal rubbing sounds. In fact, the brakes are silent. Should I be looking for leaking seals? Can the calipers be rebuilt? Should I install greese on the pistons? I guess i'll just replace both pads and rotors on the rear so they are both the same age.

BossGS4

iTrader: (2)

Yes in that specifica case of the Subaru ..... the piston was nod sticking/binding in the caliper yet the pad had worn at an angle. Upon disassembly and rebuild the caliper was fine. Other causes MIGHT have been something in the retaining clips that would keep one side of the pade from moving freey but I found nothing in the clip or in the grease that was left.

I would clean and regrease the retainer clips (where the tabs of the pads themselves slide) and the caliper slider pins with brake caliper grease

Inspect for leaky seals (i.e. the bellows around the piston) and verify the operation of the pad retainer clips your caliper slider pins.

Rebuild kits (if available) can usually be found at NAPA

mobilyte

iTrader: (3)

i have the same problem on my LS. I inspected/repaired the caliper (because of a broken bleeder valve) and turned both rotors. the other side is still super smooth, but the trouble side has warped again. i understand that the rubber brake line may be suspect, internal failure can cause bulges (not always noticable from visual inspection) that prevent the caliper from returning after the brake pedal is released. sliding pins, shims, and retaining clips are greased on a semi-annual basis.