To achieve maximum drum life and optimum performance, proper brake maintenance and brake balance are essential. Consult your truck or trailer manufacturer’s maintenance manual for proper maintenance of the braking mechanism.
The following procedures are suggested as a means of obtaining maximum service and to determine the need for replacement.
NOTICE: When replacing lining, brake drum, or rotor on one end of the axle, replace the same components on the other end of the axle. This will maintain a proper braking load on the axle.
A1. Inspection of Brake Drums or Rotors.
When relining brakes, the brake drum or rotor should be cleaned and inspected.
To be suitable for further service, the brake drum or rotor should pass the
following checks:
A. The brake surface should be free of scoring, excessive heat checks, and free
of cracks.
B. The brake surface diameter should be within the maximum diameter cast or
stamped on the drum or minimum thickness cast or stamped on the rotor.
C. The mounting holes and pilot must be round and true.
D. The mounting surface must be clean and flat.
CAUTION: If any of the above conditions are not met, the brake drum or rotor should be replaced.
A2. Turning the Brake Surface. It may be desirable to turn or resurface the braking surface to remove small heat checks or other surface defects. The following should be noted when turning:
A. When resurfacing a drum, allow at least 0.040 under the maximum diameter and on a rotor 0.040 over the minimum thickness for additional wear. For example, this usually means the drum may be turned a total of 0.080 over the brake surface diameter of a new brake drum.
Example: New Drum Diameter: 16.500
Rebore Allowance: 0.080
Diameter after the reboring limit is reached: 16.580
Wear Allowance: 0.040
Maximum Diameter: 16.620
WARNING: DO NOT TURN OR WEAR A BRAKE DRUM OR ROTOR BEYOND THE MAXIMUM DIAMETER OR MINIMUM THICKNESS STAMPED OR CAST ON THE BRAKE DRUM OR ROTOR.
The maximum diameter or discard diameter is the maximum diameter to which the brake drum may be turned or worn, and still be usable. If any portion of the brake surface exceeds the maximum diameter it must be discarded. The maximum diameter cast into the backplate portions of the brake drum supersedes all published information.
