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Old 06-09-2012, 03:40 PM
Join Date: Dec 2007
Posts: 5,061
Digital Caliper for measuring brake rotor?

Hello all, I purchased a digital caliper from NAPA auto parts. It was on sale, a good deal so to speak. I need to check the rotor thickness on the 1991 560SEL and the 1984 300DT. Can I use this device to measure the rotor thickness? I have read that I should measure the thickness in several different places.

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Old 06-09-2012, 05:00 PM
TnBob's Avatar
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Join Date: Dec 2009
Location: Shelbyville, Tn
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Yes of course. They are used much like a C clamp without that much force. Best to use your thumb to close it.
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Old 06-09-2012, 05:01 PM
Can't Know's Avatar
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Join Date: Sep 2010
Location: Sunny CA
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It's not particularly easy, but you can use it.

Micrometers are best because they are a point-check whereas the jaws on the caliper get in the way. With rotors, the biggest problem is the lip that develops. You can use small spacers to get around the lips (spacers at the pointed ends of the caliper between the jaws and the surface of the rotor), then deduct the thickness of the spacers. Do this at a couple of different locations around the rotor just to be sure you have an accurate measurement.

The problem you then run into is that it's really hard to set the spacer while the rotor is on the car, and pulling them off means removing the brake caliper, etc. It's a lot of work to me...that's why I have a micrometer.

Good luck.
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Old 06-09-2012, 06:00 PM
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Join Date: Oct 2007
Location: SoCal
Posts: 651
As mentioned, unless you have a special brake disc caliper, you need to use some sort of spacer to clear the lip which forms on the edge of the disc. I use a couple of small 1/2" round by 1/4" thick magnets. Micrometers work fine but are much more accurate than you need. Even previous generations measured to the nearest 0.001" (new ones 0.0001"). You only need to measure to the nearest 0.025" or 0.1mm.

If your brakes are operating smoothly, the values won't change much at different locations. And depending on the backing plate it may be hard to measure several places unless you remove the discs. Not recommended.
Good luck.

1998 E320 Wagon
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Old 06-09-2012, 06:04 PM
Join Date: Dec 2007
Posts: 5,061
OK, I took the tool back to NAPA and traded it on the correct "Digital Brake Disc Caliper" (about $90 OUCH!). so, I won't have to use the spacer washers which should make this job easier. anyone know the thickness measurements for the brake rotors on either a 1991 560SEL or a 1984 300DT?

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