I recently purchased a micrometer and dial gauge and plan to measure for rotor thickness and runout. When using the micrometer, when I take the measurement, do I turn the adjusting barrel until the micrometer just touches the surface of the rotor or do I continue to to turn the barrel until its tight against the rotor and I can turn it no further?
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Re: C2 Measuring for Rotor Thickness
John,
The micrometers that I own have a clutch mechanism that prevents the user from over tightening the instrument. If you do not have the clutch arrangement, gently close the barrel with the thumb and middle finger until the mic. closes on the part being measured.
It's kind of an acquired feel that comes with experience. To get some practice, I suggest that you get out your feeler gauge set and make some measurements on items of known thichness. This will also help you with reading the micrometer.
Regards,
Gene -
Re: C2 Measuring for Rotor Thickness
John:
Actually, somewhere between those two positions. Turn it until it just touches, then loosen your grip on the barrel and let your fingers slip while continuing to rotate clockwise. You will develop a feel, eventually, but DO NOT TURN TOO TIGHT, as you can damage the instrument. Better micrometers have a small racheting barrel on the end to provide the proper torque automatically.
Also, the proper way to hold the mike, is with your little finger through the loop, the instrument across the palm of your hand, and adjusting the barrel with your thumb and forefinger.
JoeComment
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Re: C2 Measuring for Rotor Thickness
I'm glad someone asked these questions before me. When measuting runout - do you measure as far out radially as you can get. Any runout will be more pronounced as you move farther from the center.
BrianComment
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Re: C2 Measuring for Rotor Thickness
If I recall correctly, the '66 shop manual states that you should set-up the dial gauge about one inch from the rotor's edge.Comment
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Re: C2 Measuring for Rotor Thickness
When measuring rotor thickness you should check along three or four radials lines spaced every 120 or 90 degrees at three points - near the inside, center and outside of the friction surface.
You will find a few thou difference, and often the center may be worn more than the inner and outer portions and there may be a ridge at the outer edge.
The point of these measurements is to get an average and compare it to the minimum thickness. As long as there is no brake chatter then the amount of rotor thickness variation or runnout is not that critical.
Depending on use, rotors can look pretty knarly, but be perfectly serviceable. The front rotors on my Cosworth Vega are worn more in the center of the friction surface and they have a pronounced ridge on the outside edge. They are well scored and peppered with numerous short (no more than one-half inch) radial cracks and basically look like hell, however, they are well above minimum thickness.
The reason for their condition and appearance is over 4000 miles of race track hot laps and about six sets of pads, yet the brakes perform superbly and there is no chatter. These rotors are fully serviceable. I just have to go through a thoughful break-in process with new pads to ensure that they seat to these well "broken-in" rotors.
DukeComment
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