Warped rotors from messed up alignment

[bubbajan21]

Hello all, this is an E34 question. A few months ago, my E34 was shimmying very hard on braking and sometimes cruising. I initially replaced the front brake rotors thinking it was a warped rotor causing the vibration and the problem seemed a little better, but by no means fixed. I then changed the thrust arms with E32 bushing'd arms and BMA accidentally sent me one E34 arm and one E32 arm. I was unaware of this and installed the arms and ran them for a while (one E34 arm, one E32 arm). The alignment was all off on the passenger side wheel, it would rub on the fender liner sometimes, and the problems were all still there. I brought it to a BMW-specific shop around me and they replaced the E32 arm with an E34 arm, but now they are telling me that because of the alignment issue, all four brake rotors are warped. Does this seem at all possible to anyone? The front rotors have a few thousand miles and the rears have about 10,000. So what does everyone think? Is this possible or is that baloney?

[jlevie]

While it is possible that the rotors are warped, it is more likely that they have uneven pad deposits. Neither will be caused by alignment problems.

The usual cause of uneven pad deposits is bring the car to a stop with overheated pads. On the street it is very unlikely to occur when using OE or better pads. But ridiculously easy to do when using low dust pads.

[canakami]

They're full of shit on the arm part. Look at Pelican parts, it's the same part number for either arm. The shimmying you're experiencing is normal for an E28/24/34/32/23 due to the design of the steering system(i.e. ball joints everywhere). So fact that it's under braking but also during cruising reinforces that fact, everything probably needs a refresh. Bad alignments mess with tire wear and handling, not on forces affecting the brake rotors. Is it possible that they're all warped? Sure, if you're riding the brakes going down hill all the time, or if the calipers/pads are hanging up and overheating them in normal driving.

I would suggest taking the car to another shop for a second opinion. Also, this chassis is VERY sensitive to wheel balance. So I'd check that was well before they try and charge you for a complete brake job.

Mileage on the chassis?

[bubbajan21]

I just checked and the arms are in fact different for E34 and E32. BMA replaced the arm for me for free and acknowledged that they sent me the wrong part.

Chassis has 83K miles so I don't know that it's quite time for a front end refresh, BUT I am still running on winter wheels and tires that are nearing the end of their life so that may be a big part of my problem. It just doesn't seem very plausible to me that all four brake rotors could be warped at once.

[canakami]

iirc the only difference is the strength of the bushing, I had E32 arms on my E28 without any issues or funny business, I've been wrong before though...