I have had for years this annoying rotational squeaking noise which appears to be coming from the back of my'66. I only hear the noise after the car has been driven and at low speed in the 10 to 15mph range. I have been going through the archives about brake problems and was wondering if the squeaking noise could be the result of rotor runout? While the car has been restored, I am sure nobody has measured the rotors for potential runout. What do you think? I have never measured rotors before but, plan to get a dial gauge and measure each rotor for thickness and runout so at least I know what I've got.
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Re: C2 Rotor Runout
John,
If it is coming from the brakes it could be from runout. It could also be from a piston hanging up or frozen, or contaminated pad or pad movement in the caliper.
Wayne -
Re: C2 Rotor Runout
Hi John:
If you have a rotational squeak, I don't think rotor runout would be the most likely cause. I think that spindle bearings, U-joints, or parking brake hardware might be more likely candidates.
To see if pad/rotor contact variations due to runout are the cause, try applying the brake very lightly when the squeak is present. Usually, the slight change in pad/rotor contact will change the nature of the squeak.
A similar test will sometimes reveal whether the cause is the parking brake. With the squeak present, apply the parking brake lightly to see if the squeaking sound changes (hold the release latch so you can modulate the pressure as you do this).
If neither of these tests have much effect on the squeak, the likely candidates are U-joints or spindle bearings.Comment
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Re: C2 Rotor Runout
John----
Even with rotor runout within spec (.002" TIR for your year, but .004" is usually ok from an air pumping perspective), you may get some "squeaking". What often causes this is the rubbing of the disc brake pad backing plates against the ends of the "pad slot" in the calipers. Rotor runout, no matter how minimal, causes the pads to move laterally and this, in turn, causes the backing plate ends to move laterally in the "pad slot". Unless you have, essentially, "0" TIR, this can happen. There are aftermarket "fixes" for this which include plastic shims that install in the pad slot and plastic slit tubes which install on the ends of the pad backing plates (may require slight t******* of the backing plate ends for installation). Both are effective in eliminating the squeak. The plastic shim type things might not last a long while, though (however, for the amount of use the cars usually get, it may be a lifetime).
It's quite easy to check rotor TIR per the instructions and specifications provided in the FSM. Inexpensive dial indicators and magnetic base stands are available which will work fine for the hobbyist with only occasional need for such tools.
Of course, there are many other possible causes for a rotational squeaking. The above is VERY, VERY common, thoughIn Appreciation of John HinckleyComment
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Re: C2 Rotor Runout
John another way to determine to much runout and possibly finding that your brake pads are moving on the brake pad retainer pin and squeaking is to remove both rear tires and reverse your lug nuts and torque them down on the spindle. Support each trailing arm so they are not hanging down with the tire removed and support the rear of the car with jackstands under the frame. Start the car engage the transmission. Watch the brake pads riding on the brake disc. If you discover that the rivets that retained the disc to the spindle have been removed you could very well have runout. Be careful with your car up and doing this. Placing the removed tires under the frame rails is a safety precaution with your car on jack stands. Bairs will send you shipping boxes and you can send your complete trailing arms to have them refurbished and will never have to worry about wheel bearings, emergency brake problems, or runout.Comment
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