Re: Is it common for disc brakes to be unbalanced?
With all the rotating stuff checked and rechecked, I'd be inclined to look at the drive shaft too. I faught that one for quite a while as well, and it did end up being the drive shaft.
I'll throw this out too. If I remember right, the drive shaft needs to be balanced, but also, the drive shaft must be built right. I think it had to do with the yoke positions on the drive shaft. They need to be 90 degrees to each other, not inline with each other. I'm talking about the mounting yokes on each end of the drive shaft. If they are parallel with each other, they bulid up some harmonics when rotating, causing the vibration. I remember Hot Rod doing an article on this, maybe check their site. Also, for normal use, I think the pinion centerline and the trans centerline need to be parallel as well. For race cars, I think you have the pinion pointing down a few degrees from the trans centerline, there-by using the rotational torque of the rear end to line up the centerlines on hard acceleration.