'07 Z4 Brake issue.

[montero1]

Had the rims on my Z4 powder coated. Wheels were off the car for close to two weeks, car sat on jackstands outside (under a car cover,the rotors were covered). Since re-installing the wheels, when I apply the brakes, I get a bad vibration, like the rims are warped. Sometimes it'll pull the steering wheel back and forth, and it feels like the majority of the vibration is coming from the left front. I re-installed the wheels myself, I am certain they aren't over-tightened. What could have gone wrong?

The car sits for months/weeks at a time.
A few mechanics have suggested that since the car sits so much, the rotors are kaput because rust forms that can't be scrubbed off. Most all of the local mechanics say the rotors can't be turned, since they are already thin and it would make them even more susceptible to warping. One even suggeted getting some high-end rust resistane Brembos if it's going to sit, or soak both sides of the rotor in penetrating oil during storage.
I've let a lot of cars sit for weeks/months, and none of them have ever had this problem.

I'd hate to get new rotors, only to have this happen again. I don't drive THAT aggressive, as in a track day, and only occasionally do I get on it in the curves. Suggestions?


Car only has 18k on it, I bought it a year ago with 9700k.

 

[dparm]

Try re-bedding the brakes:

http://www.zeckhausen.com/bedding_in_brakes.htm

 

[Rand]

you make alot of assumptions and didnt do any troubleshooting(that you told us about anyway)

Cant really recommend anything except troubleshooting the problem instead of throwing parts at it.

you tightened with a torque wrench to the proper torque?

the rust on rotors sounds pretty bogus.

translation: not enough info

 

[51Plymouth]

I have an idea - the same thing happened to me twice, on two different cars of the same model. 1989 Mitsubishi Galant. I had both cars up on blocks, each for about a month or two with the wheels off. Put wheels back on, all of a sudden on each car one or both front rotors are "warped".

In my cars, the front wheel nuts hold the rotor tightly to the hub.

What I think happens is with the wheels and wheel nuts off for extended periods, the rust between the rotor and hub shifts slightly or expands or something, or the rotor becomes slightly loosened and does not tighten back in the same way. Then when you put the wheel back on, the rotor is not perfectly parallel to the hub anymore because of rust or specks of debris that got between the rotor and hub.

I think this condition can be worsened when pressing the brakes with the wheels off. This could cause the rotor to move off the hub, and rust and debris will be uneven between the hub and rotor.

When my wheels will be off for anything longer than a simple tire change, I get some washers the same thickness as the rim, and tighten the wheel nuts back on. (This depends on what kind of wheel nuts you have. The open kind you can just turn over so the flat side will be holding the rotor on.) Then the nuts are holding the brake rotor tightly to the hub the same as if the wheel is on.

I haven't had any problems since doing this process.

You might just have to check and do a very thorough cleaning of the hub and rotor mating surfaces.

 

[double vanos]

I believe 51Plymouth has it nailed. Pull the brakes apart and scrub the rust off the rotors and hub assy. Good place to start anyway.

 

[The Critic]

Try using a wire brush to clean all of the rust off the rotor hat before mounting the tires.

 

[Hounds]

Montero1, you have a PM, sir.

 

[montero1]

Thank you for all the intelligent responses! Btw, I did try rebedding the brakes, it didn't help, so I'll go the way of cleaning the rotors.

 

[montero1]

Sprayed the rotors down, sanded them real good with emory cloth. I did see on the left front two high spots that seemed to go away with the sanding. Took it for a spin, immediately thought "wow, way better", but as I kept on braking throughout the next 10 mins, it got back to it's old pulsating self. At least I think I narrowed it down to the problem being in the front.

 

[bigjl]

Build up of surface rust where the wheels mounts on perhaps?

This area is normally kept covered by the wheels when cars are parked for extended periods of time, which is the difference between this period of time and previous.


Or maybe one of the calipers has siezed slightly as they are also normally kept protected slightly by the wheels.

 

[Tosh]

Maybe the powder coating threw off the wheel balance? Maybe the wheels went back on in a different 'clock' position, aggravating the problem? Try rotating the LF by ~180 degrees?

 

[montero1]

Originally Posted By: bigjl
Build up of surface rust where the wheels mounts on perhaps?

This area is normally kept covered by the wheels when cars are parked for extended periods of time, which is the difference between this period of time and previous.


Or maybe one of the calipers has siezed slightly as they are also normally kept protected slightly by the wheels.



Well I replaced both front rotors today, problem solved. Replaced them with cryogenics from tirerack.com. Maybe I just need to drive it more often, but I know the problem only occured after I Had the rims off for a while. The car sat an awful lot in the 9 months prior with no problems. Furthermore, the brakes were fine towards the beginning of my last trip to Georgia. Somewhere in the middle they started acting up, may have happened while I was on some backroads when I dipped off the highway due to traffic. Thanks for all the help though, sanding them was at least worth a try.