warped rotor 7k miles on new brakes

[jmgtp]

Over the past thousand miles or so the steering wheel has had a slight shimmy at speeds over 20 mph - only when I brake. Every indication is that it is a warped rotor on the front end.

I changed my brakes about 7k miles ago. I used the OEM rotors and had them machined. I'm going to pull the rotors out next weekend and have them machined smooth again, but what would cause them to warp? They were on the car for over 60,000 miles without a problem and then in under 10,000 miles on a new set of pads they warp. I don't abuse them and they had a gentle break-in. The only real change is that I am using Hawk HPS Ceramic Brake Pads. Is it possible that these generate more heat than the rotor can handle?

[ronemus]

It's actually very rare for rotors to warp. The problem is actually the organic binder used in the OEM pads; it cooks out and deposits on the rotors after hard braking to a full stop (see Stoptech's white paper on the subject at http://www.stoptech.com/tech_info/wp_wa ... disk.shtml (http://www.stoptech.com/tech_info/wp_warped_brakedisk.shtml)). The solution is good brake pads (I like Hawk HPS) and proper break-in of the pads.

[rougeben83]

Don't machine. Just get a wire brush or some sandpaper, scuff the rotor surface and clean with brake cleaner.

Bed the pads as usual and you're good to go.

You need to be aggressive with your bedding. NOT gentle. I usually do 4-5 medium stops from 40mph, then a couple of hard stops from 50-60mph and drive around a bit to let the brakes cool down.

[jmgtp]

In 60k+ miles the rotors never warped on the OEM pads so I don't think they are the problem.

I always machine rotors on any car that gets a new set of pads and never have problems. I don't think I did anything special for break in or to bed the pads in - just drove normal. I'm going to chalk this up to 'shit happens' have the rotors cut and move on. Hopefully it doesn't happen again.

Anyway, this is the first I've driven the Subaru in about 5 months! The morning temps are just too cold now for the summer car and a cold clutch in that car is very harsh. Its nice to be driving something civil without a big lopey idle.

[97legacygt]

Don't automatically assume it is the rotor; it could also be that the hub is warped. Also like rougeben83 said, make sure the surfaces are clean on both the hub, the rotor where it attaches to the hub and where the wheel is mounted to the rotor. If there is a little bit of rust or dirt, it can make it seem like something is wrapped.

[2.5GT]

Driving habits :neutral:

[jmgtp]

If it was the hub wouldn't it have the shimmy all the time and not only when on the brakes? I assume you mean rust build up between the mating surfaces of the hub and brake rotor? I still haven't gotten around to pulling it apart, I always get tied up fixing someone else problems and never my own.

I don't think it is driving habits, I don't abuse this car, that's what the other car is for.

[97legacygt]

If it was the hub, if it was severe enough you probably would feel it all the time. I think if it is only a few thousands of an inch of, then you would feel it only when braking. If you have a dial indicator, you could check if the rotor or hub or both are warped. If you don't, you can probably get a cheap knock off brand for super cheap.

Yeh, I do mean the mating surfaces of the bub and rotor.

[jg09]

My '02 had pretty warped rotors at only 84k when I got it. When I picked it up off the lot, the rotors were already well warped by that time (combine that with the little bit of body damage and the dirty interior and I got 4k off the asking price!). Mine had got to the point where if you turned the wheel just slightly under minimal brake pressure, the whole steering system would start clunking and the wheel would feel like it was being ripped out of your hand. Funny thing is, when I took the rotors off, we could hardly tell that they were warped. They looked brand new.

[ivwarrior]

I always machine rotors on any car that gets a new set of pads and never have problems.

You shouldn't. Why waste rotor material if there's nothing wrong with them?

I'm going to chalk this up to 'shit happens' have the rotors cut and move on. Hopefully it doesn't happen again.


It probably will. I doubt there will be enough rotor mass left after machining them a second time. Save yourself the trouble, buy new ones, and make sure to properly torque your lug nuts when putting the wheels back on.

[jmgtp]

Subaru rotors must suck if they cant handle one or two cuts. I dont think thats the case tho or i would have 4 warped rotors and not just one. Machining rotors is a fairly standard practice when servicing brakes. I just need to get around to doing it.

[ivwarrior]

MOST rotors these days can't handle more than one cut. Just one of the reasons why you should machine them needlessly.

[outbacktweaked95]

^^^ in the garage we rarely if ever machine rotors and never ever get the rotors machined when there brand new. I mean there machined form the factory to their specs its kinda dumb to have them done again without doing anything but pulling them out of a box. Also sanding them down and wire brushing is not a good idea if they get to thin and get hot from braking thetll get stress fractures and explode. trust me its not good at all.