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Q's on Brake Inspection Terminology....Runout, Warpage, etc.... 200

posted by  matt82dl on  Mon Oct 18 01:53 CST 2004
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last visit: Mon Oct 13 10:46 CST 2014
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I'm trying to diagnose some steering wheel shudder under high speed braking in my 940. I have been reading the FAQ and there seems to be plenty of good info in there, but just need a little clarification on the terminology.

Thickness-- OK, this is easy, use a micrometer to measure multiple points on the rotor. What is the spec??

Runout-- When I think of runout I think of a drill bit being crooked in a chuck. I have a test indicator and mag base. How should I check runout. Pull the rotor and check run out of the hub??

Warpage-- Would I measure this by placing test indicator on rotor and then rotate the rotor?? Is the spec .003"??


This is a new to me car, and it was driven in downtown Chicago for years. I suspect that the strut rod bushings might need to be replaced... thoughts on poly vs. rubber??

Thanks for you input.

Matt

--
'82 DL - 158k, '93 945 - 116k








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    Q's on Brake Inspection Terminology....Runout, Warpage, etc.... 200

    posted by  someone claiming to be 240snowmobile on  Mon Oct 18 03:27 CST 2004 [RELATED]

    I don't know offhand what the min thickness is for the rotor, but the spec is always stamped or cast somewhere on the rotor. You might have to take a wire brush to clear the crud and read it. There is usually not much reason to measure more than one place on a rotor, but in your case I guess it wouldn't hurt.

    Set up your base and dial indicator (preloaded and zeroed) pendicular to the rotor, closest to the outside edge but within the pad area. Grab the rotor on opposite sides and check for bearing play. Rotate the rotor and check for runout/warpage (synonyms). If the runout is excessive remove the rotor and check the hub by itself to try and determine whether the rotor or the hub/bearing is the contributing factor. Repeat for both braking surfaces of the rotor and on both sides.

    I had a pair of junk R.O.C. rotors that were so poorly cast (the vents did not follow an even centerline) that were within spec when measured cold but they warped badly once they heated up. I promptly returned them and that was the last time I "saved money" on disposable rotors.

    Don't forget to check your tire/rims and bushings as well.







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