When removing the parking brake drum, thoroughly clean and inspect the drum for the following conditions:
| • | Cracks |
| • | Scores |
| • | Deep grooves |
| • | Out-of-round |
Surface Finish
Clean slight scoring with an emery cloth. Heavy or extensive scoring causes excessive brake lining wear. The drum braking surface will need machining in order to remove these scores.
Do not machine the drum if the drum is grooved and the brake linings are slightly worn. Polish the drum braking surface with a fine emery cloth. Eliminating all of the drum grooves and ridges on the lining requires removing too much metal and lining material. If the grooves and ridges match, leaving the drums alone is satisfactory service.
Inside Diameter Check
Measure the inside of the brake drum at two or more places around the circumference of the braking surface. Perform the measurements at the same distance from the edge of the drum.
Taper Check
Measuring the drum for taper involves taking measurements at the inner and the outer edges of the machined surface at two or more places around the drum.
Cracked, Scored, or Grooved Drums
Replace a cracked drum. A cracked drum is unsafe for further service. Do not weld a cracked drum.
Smooth up any slight scores. Heavy or extensive scoring will cause excessive lining wear. If there is excessive lining wear, resurface the drum braking surface.
If the linings are slightly worn but still reusable, and the drum is grooved, polish the drum with a fine emery cloth. Do not refinish the drum. Eliminating all the grooves in the drum and smoothing the ridges on the lining requires the removal of too much metal and lining. In order to obtain satisfactory service, leave the grooves and ridges alone so that they match.
If you are replacing the brake linings, always refinish a grooved drum. Using a grooved drum with a new lining will wear the lining and make proper brake performance difficult to obtain.
Out-of-Round or Tapered Drums
An out-of round or tapered drum prevents accurate brake shoe adjustment. This type of drum is likely to cause excessive wear of the other brake parts due to its eccentric position. An out-of-round drum can cause severe and irregular tire tread wear as well as a pulsating brake pedal. When the drum exceeds the specification limits in taper and/or out-of round, refinish the drum in order to true up the braking surface. Measure out-of-round and taper accurately by using an inside micrometer and extension rods.
When measuring a drum for out-of-round and taper, take the measurements at the open and closed edges of the machined surface and at right angles to each other.
