Surface Finish
Whenever brake drums are removed, thoroughly clean and inspect the drums for the following conditions:
| • | Cracks |
| • | Scores |
| • | Deep grooves |
| • | Out-of-round |
| • | Taper |
Some minor surface wear is normal and will not affect brake operation. However, the inside diameter should never exceed the maximum specification. Refer to Inside Diameter Check for more information.
Always replace a cracked drum because a cracked drum is unsafe for further use. Never attempt to weld a cracked drum. Smooth up any light scores. Heavy or excessive scoring will cause excessive brake lining wear and it may be necessary to resurface the drum braking surface.
If brake linings are to be replaced, always refinish a grooved drum. A grooved drum, if used with a new lining, will wear the lining and make proper brake performance difficult to obtain.
If the brake linings are slightly worn (but to be reused) and the drum is grooved, polish the drum with fine emery cloth but do not refinish. Eliminating all of the grooves in the drum and smoothing the ridges on the lining requires the removal of too much metal and lining. If left alone, the grooves and ridges match and satisfactory service can be obtained.
Inside Diameter Check
Before refinishing a drum, measure the inside diameter. During refinishing, only remove enough metal to obtain a true, smooth braking surface.
If a drum will not true up when refinished to the maximum allowable inside diameter specification, the drum must be replaced.
If the inside diameter exceeds maximum limits, proper heat dissipation will be adversely affected and may cause distortion of the drum.
Ensure that the maximum inside diameter of the drum meets the following specifications:
| • | 182 mm (7.16 in) for a 2-Door model |
| • | 202 mm (7.95 in) for a 4-Door model |
Taper and Runout Checks
An out-of-round or improperly tapered drum makes accurate brake shoe adjustment impossible. It is also likely to cause excessive wear of other parts due to its eccentric action. An out-of-round drum can also cause severe and irregular tire tread wear and a pulsating brake pedal.
When the drum exceeds the specification limits for out-of-round and/or taper, refinish the drum to true up the braking surface. Replace the drum if the drum cannot be brought within specifications by refinishing.
When measuring a drum for out-of-round, taper, and wear, take the measurements at the open and closed edges of the machined surface and at right angles to each other.
Runout is a low spot in the roundness of a drum. If runout exceeds maximum specification, replace the drum because improper stopping or pulsating brakes could result.
Use the following specifications:
| • | Out-of-round (Maximum) - 0.01 mm (0.0004 in) |
| • | Taper (Maximum) - 0.1 mm (0.004 in) |
| • | Roundness (Maximum) - 0.04 mm (0.0016 in) |
Balance
When brake drums are manufactured, the brake drums are balanced and weights are welded in place as required. Do not remove any of these weights. The balance of the drum can usually be checked on an off-vehicle balancer. An out-of-balance drum must be replaced.
