Last week, I took the M3 back into Bavarian Machine for its “break-in” service, necessary after the engine was rebuilt. They like to retorque the head studs to make sure that everything seats nicely, and that there are no more problems with the head gasket.
While it was in there (there’s that expensive phrase again), I had them look at my brakes. At the track in mid-February (LSRPCA event at TWS), I had the brake shimmy problem again. Once the brakes got hot, and only when the brakes were hot, the whole front end of the car felt like it was shaking apart every time I put my foot on the pedal. When the brakes cooled down, the shimmy went away. So, the track weekend was fun, but the brake problems were really frustrating me, especially since I thought they were solved before.
When I was changing my pads after the event, I noticed that the dust boot on one of my front calipers seemed not to be seating correctly. So, I asked BMS to take a look at all of the calipers, and briefed them on my braking problems.
Turns out that both of my front calipers were bad. Both dust seals had gone bad, and the pistons were completely rusted/scored/pitted. This explains the behavior on the track; once the brakes got hot, the pistons expanded just slightly, but enough to cause binding on the inside of the caliper, causing inconsistent caliper clamping action. Rear calipers were fine.
It was actually cheaper to put some new calipers on the front than to rebuild them, especially because the pistons would have to be replaced. So, that’s what they did, in addition to putting on new rotors all the way around.
But, the best news is in the next post.
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