Question for any mechanics

[chris4001asat]

I had brakes put on my wifes car 4 months ago. First time ever that I didn't have to replace rotors, and I'm 41. She commented a few days later that the steering wheel shook when she hit the brakes. I drove it around the block and felt a little vibration, but thought it came from just resurfacing the rotors. We went on vacation a few weeks ago, I was driving, I hit the brakes coming off the Eway, and had my arms and head just about shake off of me. I've been going to the same garage for a good 5 years, but the last few times, I've kind of questioned a few things they told me. I went to a different garage to have them look at the brakes, and they said it looks like the rotors were never turned by how glazed over they were. I went back to the original garage and told them about the vibration, and that it started after the brake job. They said the rotors might need to be turned again, for a charge, or they might need to be replaced, at a higher charge. He said the rotors should have been turned at the original brake job, that its included in the price.
Can you tell by looking at rotors if they've been turned recently? Any other thoughts?
Thanks to all who reply

[bobba66]

I would change the rotors. On newer cars the rotor are thin to start with. Not much material for resurfacing. Also, make sure your ball joints, tie rod ends etc. are in good shape. Any slop in the steering or suspension can cause a vibration.

[T-Bird]

Hi.

They still turn passenger car brake rotors in the good old US of A???

You're kidding, right?

The last ones that I've seen were in the nineties, after that the minimum thickness has been so close to the thickness when new that only grinding could remove the hardened surface gently enough.

If and when I turn rotors or drums (yes I have a special lathe for that), the fee is roughly 50€ for the small (>14") ones and 100-200€ for the big 'uns (14"-30"), cash .

If the rotor is vented, a condition You described happens as the ridges between the surfaces rust and the whole rotor starts to flex under the load.

If that's the case, EVENTUALLY THE RIDGES WILL BREAK AND THE ROTOR WILL SHATTER, in the worst case taking the caliper and parts of the suspension arms with it. In any case that wheel will lock, and the game is lost.

Please do You and your wife a favour and tell the hack-job garage to stick it and buy new rotors.

Regards
Sam

[Johnny Crab]

Originally Posted by T-Bird

Please do You and your wife a favour and tell the hack-job garage to stick it and buy new rotors.

Regards
Sam

+1
The rotors on my Chevy Tracker had a similar vibration issue but were "turnable" but only this time. Next time = new rotors.

BTW, What kind of car is it?

On our larger vehicles, I usually replaced rotors myself(and repacked bearings, etc.) but that's me. I did not trust making the thickness smaller as outlined in the previous post. IF you DIY, rotors for common vehicles are quite reasonable at all autoparts stores.

Also if it is a Ford Taurus, our daughter had one with a similar vibration-when-braking issue. The brakes were fine but research showed a design flaw(cost-savings?) in that the factory tie rods are extremely fragile and one was in bad shape at its connection points. New tie rods cured the vibration.

[Mike N]

I would have replaced the rotors before turning them. And assuming they were cut at the last brake job, there is no way there's enough material left to take another cut out of them.

Anyway, you should be able to tell if the rotors were turned or not. Hopefully they cut the entire braking surface, and not just the area where the pads ride (typically there is a little extra surface in the face of the rotor that the pads never touch). Look at the surface of the rotor near the center hub and see if it looks like it was cut. If it's all rusty they probably never turned them.

In any event, you'll need new rotors to cure the pulsation. No way would I try and turn pulsating rust belt rotors, you're just asking for trouble. Hopefully the shop that did the work would credit you whatever you paid for turning the rotors towards a new pair of rotors.

[chris4001asat]

It's a Mazda 5. A small minivanish wagon kind of thing. When I mentioned about any kind of warranty for the rotors, he said no. Kind of pi$$@* me off a bit. 2 complete sets of tires, countless oil changes plus other stuff. You'd think he'd want to keep a steady customer happy.

[Pilgrim]

It's almost certainly warped rotors caused by rotors being too thin and warping due to heat.

You can't eyeball them, you use calipers to measure their thickness - if the thickness of the rotor is under the minimum, you don't turn them or re-use them when replacing the brake pads - you replace them. Because if they get any thinner, they will warp from the heat of operation as yours have.

I don't have any problem with re-using rotors on most vehicles, but some are specifically designed not to be re-used and must be changed with every set of pads (Audi and BMW often do this). Regardless, all rotors have a minimum thickness spec which must be observed when changing brake pads. If the rotor is less than that thickness or turning would reduce it to less than that thickness, you just don't re-use it.

Rotors aren't just friction surfaces - they're also heat sinks, and that function is just as important as their role in creating friction. The energy generated by the friction created in stopping a car is turned into heat...and metal can only stand so much heat before warping.

Where your shop could potentially be very wrong is that if rotors are too thin, turning them again would only make them operate worse because there is even less material to act as a heat sink. I suspect that's why they mentioned that replacement may be required...because every mechanic knows this. My suggestion to you is that if you replaced the pads and the rotors warped, they're already too thin and you should assume they must be replaced.

Mike N is absolutely right. You need new rotors. Get them.