Brake Rotors

[ErikT]

Can OEM rotors be resurfaced?

I had my "new" E30 inspected two weeks ago at Merchant Tire in Bethesda. It is not the first time I've had issues with them, but since the shop is two blocks from my house the convenience always lures me in for minor stuff.

After dropping my car off for inspection the svc. manager calls and informs me I need rear brake pads to pass inspection ($200). I used to do that kind of thing myself but I was anxious to get my "new" car road-legal so I said "OK". He calls again asking if I want to replace the rotors as well ($200). After telling me they were within spec, I said "No thanks, just resurface them".

They squeek occationally. A week goes by and the squeek turns into a squeel. It has now morphed into screeching.

I take the car back and show them how the brake pad appears to be making contact with the non-polished part of the rotor. Turns out, the rotor is "cupped" and wasn't resurfaced "because that kind of rotor can't be resurfaced"?!?. I'll be screeching until the pads get grooved. Obviously, had I known that, I would have told him not to fix anything and I'd swap new rotors and pads in myself. I felt bad enough paying them to swap the pads...now I'm going to have to take it apart anyway.

Are these guys completely full of it? I guess I thought all shops resurfaced rotors if they replaced brake pads...isn't that standard procedure?

I'm waiting till Bob, the service manager gets back from vacation before calling & getting to worked up.

-Erik

[AG]

Can OEM rotors be resurfaced?

Yes and no. There is nothing physical about the rotors preventing them from being resurfaced. However, BMW specs 1.6mm of wear from new (at least on the E46) whereas most other manufacturers spec 2.0mm+ of wear. Once you've put some wear on the rotors and then resurface them, you're basically at minimum thickness. If you're not doing the work yourself, from a labor/cost point of view, it makes more sense to replace the rotors rather than resurface them when replacing pads. If you can do the work yourself, just replace the rotors when necessary.

[ErikT]

AG, Thanks for the info.

When I used to do that myself I always replaced the rotors, it was wayeasier than having them resurfaced anyway. I was too busy/lazy to deal with it. I guess if they had told me they weren't going to resurface them I would have handled the whole thing differently.

[SharkD]

The screeching may be due to an improper replacement of the rear calipers - if the anti-rattle clip wasn't re-installed the pad carrier and the pads will vibrate and make the "squealing" noise. You might want to pull your rear wheels (or look through the wheel spokes) and see if there's a metal clip that looks like part #7 in this parts diagram.

Regardless, waiting for the pads to "groove" is dangerous -- until those pads fit the shape of your rotors, you're driving with only a small part of the rotor surface in contact with the pad.

Just so you know, a set of Mintex rear stock "street" pads for an E30 run $34 at Bimmerworld and a pair of stock rear rotors is $59. Changing those pads and rotors takes about a half hour.

[Scotty]

I don't want to hijack this thread, but I do have a related question.

I'm getting set to install new rotors and high-perf pads. Should I use old pads to "bed" the new rotor before bedding the new pads?

[OwnedbyDuncan]

What pads? I would use the new pads with new rotors that way whatever material the pads deposit on the rotors will be the same. I usually let the pads and rotors acclimate to each other for 200miles or so and then bed the pads in and off gas them. If I had a DS or autox might have to use a different method.

[1996 328ti]

I don't want to hijack this thread, but I do have a related question.

I'm getting set to install new rotors and high-perf pads. Should I use old pads to "bed" the new rotor before bedding the new pads?

You are bedding in the pads, not the rotors.
If I don't outgas brand new pads before a track event, the first session is a little scary. The car will not track straight under moderate braking.

[mlytle]

original poster got hosed on the prices. as sharkd said, pads and rotors are CHEAP for these cars and it takes 15-30min per corner to do all the labor.

bedding in pads is a 1/2 lap deal. drag the brakes coming out of the pits down the main straight at summit, a few more hard stabs before getting to turn 5 and they are ready for full tilt boogie on the green flag lap.

[Scotty]

FWIW, I found an interesting tech article and FAQ at StopTech.

A friend was informed by Wilwood that new rotors typically should be treated to a few low-intensity heat cycles to "temper" the metal. Pads should then be treated to a different set of rising-intensity heat cycles to transfer pad material to the rotors and outgas the compound adhesives. I can't find solid validation for the rotor-tempering process but the pad bed-in is common knowledge.

From what little I know about hardening steel, it seems sensible that the rotors, after being cast and machined, may need to be heat-treated before being lit up in racing conditions...?

[chicane]

Yes and no. There is nothing physical about the rotors preventing them from being resurfaced. However, BMW specs 1.6mm of wear from new (at least on the E46) whereas most other manufacturers spec 2.0mm+ of wear. Once you've put some wear on the rotors and then resurface them, you're basically at minimum thickness. If you're not doing the work yourself, from a labor/cost point of view, it makes more sense to replace the rotors rather than resurface them when replacing pads. If you can do the work yourself, just replace the rotors when necessary.

It depends on the car as to whether the cost benefit is still there but in large part you are correct. When you factor in taking the rotors off then down to the machine shop, and I don't know what your shops charge but now it is something like $15 -20 to turn a rotor, and bringing them back installing, you might has well just replaced. It used to be $5 at Trak Auto I remember.

[M-technik-3]

Ok us E30 guys should have a DIY fest. Pool knowledge together and do projects on each others cars.

I need to do two more Timing belts this week and head gaskets if some one is bored...

[1996 328ti]

Well we have a DIY coming up in Sept at FunkTion Auto.
5 lifts, 2 techs to help.
I'm replacing front rotors and pads this Saturday at Convenience but just notices I should probably replace the rear rotors too. Need to pick up pads first.

[M-technik-3]

Yeah, saw that figured most of us have things that take more time like the wheel bearings and rear sub frame issues. These will take more time than simple diy oil change , ecu chip swaps and the like things that I have seen at diy events at other chapters.

[OwnedbyDuncan]

Greg,

Dont forget on mine timing belt and water pump were done late last fall.
Bill Shook at Kraftwagen has all the service records.

Dave Apker

[M-technik-3]

No I haven't Dave, It's the Eta Sport and a i that need to be done.