In the August ’95 Tech Talk column, Fred Metzler Jr. wrote a letter describing excessively rapid brake-pad wear on his ’93 Typhoon. Your response indicated that you also experienced similar wear on your ‘9 I Syclone. Let me describe what I found to be the cause of my problem and what I did to fix it.
My symptoms were excessive brake dust on the front wheels and poor braking efficiency. Inspection of the rear drum brake shoes showed slight, normal wear. Inspection of the front pads, however, showed that the outer pads had worn completely through the pad material and were rubbing the metal backing plates on the rotors, thereby destroying the rotors. (The audible wear indicators are affixed to the inner pads, thus I had no audible indication of the rapid wear problem.) Checking the service manual, I found that there should be between 0.010- and 0.024- inch total clearance between the ends of each caliper and the steering knuckle. (Use a feeler gauge, measure clearances at each end of the caliper and add the clearances together.) Both calipers measured well below the minimum tolerance.
Heat generated during braking was causing each caliper to expand and bind in its steering-knuckle mounting. During braking, hydraulic pressure overcame the friction, and the pads moved against the rotor. However, upon release of brake pressure, only the caliper piston and inner pad would retract. The caliper remained stuck in its mounting, holding the outer pad firmly against the rotor, wearing the outer pad and continuing to generate heat, which continued to bind the caliper in its mounting.
The fix was to disassemble the calipers from their mountings and to hand file (using a mill file) the steering knuckle to provide the proper clearance. Since this is a “cut and try” operation, it should be done in several small, careful steps. It’s easy to remove too much material and wind up with brake calipers that “clunk” with each brake application.
Following the replacement of all worn parts with GM service parts, I have had much improved braking and only normal wear for the past 30,000 miles (about half pad depth). Yes, these brakes are relatively small for the application, but they have proven adequate for my 65,000 miles worth of daily street driving. You just have to remember their limitations.
JOHN R. BELL Marysville, WA
Thanks for the advice. Readers, this problem can occur on any late GM chassis running Moraine floating calipers. The required caliper-knuckle clearance varies per year and chassis-check your service manual.