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I was trying to measure run out on my brake discs to see if I need to replace or shim them and I kept getting wild all over the place readings as I turned the axle. All four lug nuts where snuggly in place, and the brake pads had already been removed. The first thing I have to say is I'm not sure if I'm reading the dial caliper correctly.

I set my dial meter to about zero:

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Then I pushed on the disk with my thumb and the dial indicator moved left about 0.16mm:

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Then I pulled on it and the dial moved to the right about 0.42mm:

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So I've got about 0.59mm play in the brake disk. Run out is supposed to be a max of 0.07mm, and axial end play on the front wheel bearing is supposed to be 0.05mm. Do I have bad wheel bearings ( they were actually a bit hard to rotate ) or could this be something else?

  • Where do you attached the "foot" of the dial indicator? – Martin Jan 9 '17 at 15:07
  • @Myself To the top of the brake caliper cover. You can see it best in the first picture to the right of the needle. – Robert S. Barnes Jan 9 '17 at 17:01
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If you are pushing and pulling on the brake disc then you are measuring the play in the bearings. To measure the run-out of the disc, you should rotate the disc slowly and note the maximum and minimum readings without pushing or pulling on the disc. The pointer should be as close to the maximum diameter of the disc - or at the distance specified in the manufacturers manual.

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    But is that the proper way to measure the play in the bearings? Or do I need to remove the brake disc and measure on the hub? – Robert S. Barnes Jan 8 '17 at 19:37
  • What are you trying to measure : if you want the run-out on the disc then rotate the disc etc as explained, if you are wanting to measure the play on the bearings, then you need to proceed as you originally explained, but at the correct distance as the further you measure from the bearing the larger the measurement... – Solar Mike Jan 9 '17 at 8:45
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So after doing a little youtube research I saw that to check the bearings I need to put the tire back on and then try to wiggle it back and forth. I did that and there was quite a bit of back and forth play, so it seems pretty obvious now that the wheel hub bearings are shot.

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