Odd wear on rotors?

[metolious69]

I have a 2000 4WD Tahoe (110,000 miles). I had some vibration/shimmy when I applied the brakes. I replaced the front brake pads and this seemed to stop the vibration only for a short time. I've had mechanics look at the rotors and they checked out fine. So the vibration (when braking) is back and I'm not sure what to check next.

I did notice that the front rotors had some odd wear. There was a slight rust build up on the outside edge and the inside edge (where the brake pad surface comes into contact with the rotor surface). Its about 1/4" in depth. I thought that when I installed the new pads, that this would be worn away when I applied the brake. The rust build up is still there. The 'rusted' area actually wore a grove into the old brake pads. The rust seems brittle to the touch and I'd expect it to wear away when braking.

Not sure what to check next or what may be causing the vibration when braking. Should I go ahead and have the rotors turned? Could this vibration be coming from the rear (pads/rotors)?

Any suggestions?

[mtmaurer8ooo]

Yes, it could, assuming that you have rear disc brakes but it may also be the front, or it could be from both. I feel bad to be the one to tell you this, but you wasted money on those pads. One of the cardinal rules of brakes is that only put new pads on clean rotors. What I mean by clean is new or turned - you have to have a 'new' surface to mate the new pads to, or as you found out, you will ruin your new pads. So realistically, you should have turned or replaced the rotors in the first place. Past that, we need some more info. How did the tech check the rotors that he said were fine? Did he just look at them? Mic them? Gauge them to see if they are/were in fact true? Let us know some more about her if you can, and we'll go from there. M.

[metolious69]

That makes sense to turn the rotors before installing new pads. To my knowledge, the mechanic probably just ran his finger across the rotor surface and assumed that the surface was true.

I believe that I will go have the front and rear rotors checked (turned or replaced), then install new pads.

What does it usually cost to have rotors turned and do you know the cost of new ones.

Thanks

[maxwedge]

A dial indicator will determine which rotor is causing the problem, by measuring runout, rust build up between the rotor and hub can also cause this.

[metolious69]

Can anyone tell me why I would have the rust build up on the surface on the rotor? Shouldn't the brake pad wear down the rust when it contacts the rotor. The brake pad surface covers the entire area of the rotor surface. It just doesn't make sense.

However, I do plan to have the front rotors turned in a couple of days and install new pads and see if that takes care of the vibration. If not, then I'll attack the rear pads and rotors.

Thanks for the info.

[maxwedge]

I said between the rotor and hub, which refers to the rear of the rotor to the wheel mount hub, not the braking surface or wheel mount surface.

[metolious69]

I understand what you were referring to, but I doesn't answer my question about the rust build up on the braking surface of the rotor and why the brake pad would wear down the rust on contact.

[wonder squirrel]

Does the rotor have imbedded rust on it, or just flash rusting?

[metolious69]

The rust does not appear to be imbedded. I looks like surface rust.

What are the remedies for imbedded verses surface.

[metolious69]

I just replace both sets of rotors and the vibration has been eliminated.

Thanks for the info.