Clean and inspect the brake drum any time the brake drum is removed. Check the brake drum for the following conditions:
| • | Cracks |
| • | Scores |
| • | Deep grooves |
| • | Out-of-round |
| • | Taper |
| • | Surface finish |
If any of the above conditions exist, use the following information tin order to determine if the drum can be returned to service.
Cracked, Scored, or Grooved Drum
A cracked drum is unsafe for further service. Replace cracked drums. Do not weld a cracked drum.
Smooth any light scores. Heavy scoring causes excessive lining wear. You may have to resurface the drum braking surface.
Polish the drum with fine emery cloth if the linings are only slightly worn. Eliminating all grooves in the drum removes too much metal and lining. 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 Drum
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 |
When the drum exceeds the specification limits in taper and /or out-of-round, refinish the drum to true up the braking surface.
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).
When measuring a drum for out-of-round and taper, take measurements at the open and the closed edges of the machined surface and at right angles to each other.
- 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.
Surface Finish
Light scoring can be cleaned up with a fine emery cloth. Heavy or extensive scoring causes excessive lining wear. The drum braking surface will need machining to remove these scores.
If the drum is grooved and the brake linings are slightly worn, the drum should not be machined. Instead, polish the drum braking surface with a fine emery cloth. Eliminating all of the drum grooves and ridges on the lining would require removing too much metal and lining material. The grooves and ridges match and satisfactory service can be obtained by leaving them alone.
Inside Diameter Check
Measure the inside diameter of the brake drum at two or more places around the circumference of the braking surface. The measurements must be made at the same distance in from the edge of the drum. Compare the results with the wear specifications. Refer to Component Specifications .
Taper Check
Measuring a drum for taper involves taking measurements at the inner and outer edges of the machined surfaced at two or more places around the drum. These measurements should be equal.
