by Norman Nock
Originally published in the Austin-Healey Magazine, January 1994
There are certain frequencies (noises) that humans react negatively to like a baby crying, sirens and screeching brakes. The noise from brakes is always there but is dampened out by the large mass of the brake system components but the noise becomes noticeable when components wear. If your hair stands on end when you use your brakes something should be done to stop the noise.
When your front brake pads are down to 1/16" they should be replaced. The brake rotors should also be ground when you replace brake pads to help prevent any noise. The Minimum thickness for Austin-Healey brake rotors is .325". Brake shops will not turn your rotors less than minimum. When replacing brake pads the locating pins and shims should be replaced. A kit made by Girling is available called a "Squeal Deterrent Kit" that includes pins and shims. The shims should be lightly coated with a product that is made for British cars called PBC. Poly-Butyl-Cuppysil, #153245, looks like brown toothpaste. Other products are available made in the USA. Remember, if all you do is replace the brake pads you could still get brake squeal. Rough rotors will file and scrape away the brake pad friction material, and could cause clicking, thumping or knocking when brakes are applied.
A good test to determine the quality of the finish on a rotor is if you can run a ballpoint pen across the turned surface making a solid line. lf you get dots it is not a fine enough finish. The ideal finish is 40-50 RMS "root mean square" — the difference of peaks and the valleys.
Rotors should be sanded to remove the peaks after grinding to give a non- directional surface. Clean rotors with a commercial brake cleaner, or soap and water. Rotors will rust very quickly after they are cleaned unless the vehicle is put into regular use. If any product is put on the rotors to stop them from rusting, it would have to be cleaned off before the car is put into service.
Here's a summary of what can cause brake noise:
Rotors need to be ground.
Wrong kind of friction material.
Loose fitting calipers, bolts or abutment.
Poorly fitted pads.
Loose fitting pegs.
Foreign material embedded in pads.
Small rock touching rotor.
Also check the felt pad and adjusting peg on front and rear drum brakes; rear drum brakes on cars fitted with front disk brakes. Use PBC to lubricate the felt pad, all metal to metal moving parts between brake shoes, backing plates, and wheel cylinders. Do not put PBC on linings. Replace dust seal #BTC171 to help keep foreign materials out.
Backing Plate Adjusting Peg:
To adjust the peg, back it off until it does not touch brake shoe. Have your helper hold pressure on the brakes. Screw in peg till it just touches the shoe then lock into place. Brakes should be worked on only by qualified mechanics.
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