Clean and inspect the brake drum any time the brake drum is removed. Inspect the brake drum for the following conditions:
| • | Cracks |
| • | Scores |
| • | Deep grooves |
| • | Out-of-round |
| • | Taper |
| • | Replacement diameter |
| • | Improper balance, when necessary |
Cracked, Scored, or Grooved Drums
A cracked drum is unsafe for further service. Replace cracked drums. Do not weld a cracked drum.
Severe scoring (groove depth in excess of 1.5 mm (0.060 in) causes excessive lining wear. The drum braking surface may need to be refinished. Slight scoring can be smoothed with emery cloth.
If the linings are not worn to the minimum lining thickness and the drums are not worn to the replacement diameter, grooves can be polished with fine emery cloth. Eliminating all the grooves in the drum braking surface removes too much metal. Left untouched, the grooves and ridges match. Satisfactory service can be obtained.
Always refinish a grooved drum when replacing the brake linings. Using a grooved drum with new linings will wear the linings. This may cause improper brake performance.
Out-of-Round or Tapered Drums
An out-of-round or tapered brake drum can cause the following symptoms:
| • | Inaccurate brake shoe adjustment |
| • | Excessive wear on other brake parts because of eccentric action |
| • | Severe and irregular tire tread wear |
| • | Pulsing brake pedal |
Out-of-round and taper can be measured accurately with an inside micrometer and extension rods. The drums should be refinished if taper or out-of-roundness exceeds 0.015 mm (0.006 in).
- Measure the drum inside diameter at the inner edge of the machined braking surface.
- Measure the drum inside diameter at the outer edge of the machined braking surface.
- Record the measurements.
- Repeat steps 1 and 2 at two or more places around the drum.
- When the brake drum exceeds the specification limits in taper and/or out-of-round, refinish the drum.
Inside Diameter Check
Measure the inside diameter of the brake drum at two or more places around the circumference of the braking surface. Measure at the same distance in from the edge of the drum. Compare the results with the wear specifications. Refer to Component Specifications . Replace the drum when necessary.
Balance
Manufacturers use weights to balance brake drums. Do not remove these weights.
Inspect the drums for proper balance when maintaining wheel balance is difficult.
Inspect the drums on off-vehicle balancers. Replace the drum if it is out of balance.
