You can "see" how much run out you have by securely holding in place something like a dental pick or screwdriver. You would do well to have an assistant turn the rotor while you hold the pick on a solid platform (wooden or cement block?)so it does not move. Move the pick in until it touches the rotor while it is being slowing rotated. The distance between that contact point and the largest gap created during rotation is the runout and can be measured with a feelers gauge. This is of course a crude setup but for these purposes works just fine.

I would agree that what other people have suggested concerning cone bushings has definite merit. The pulsing on braking I was getting in my 1991 745T was indeed nothing more than worn bushings. Their replacement resulted in the problem disappearing.

Randy

Can't consider anyone who wants to learn something new a dummy.

Dial indicator is pretty easy to use. Most have a plunger that moves in and out under spring tension. There is a gear rack attached to the plunger and it drives a gear on the needle of the dial. The dial reads in .001" (mm available).

To use, you anchor the base on something stable and place the plunger against the surface of the disk. Rotate the disk and read the minimum and maximum values. Subtract and you have the runout.

I can't say how important it is to measure runout. If you are having problems with the brakes pulsatting, or if you are putting on new rotors and want to confirm they are true, it is probably a good idea.

Good luck,
Dan