Brake Drum Inspection. Pontiac Sun Runner - 4WD (Canada) 1998

For 1990-2009 cars

### Surface Finish

Whenever brake drums are removed, they should be thoroughly cleaned and inspected for cracks, scores, deep grooves, out-of-round and taper. Some minor surface wear is normal and will not affect brake operation. However, inside diameter should never exceed the maximum specification.

A cracked drum is unsafe for further use and must be replaced. Never attempt to weld a cracked drum. Smooth up any slight scores. Heavy or extensive scoring will cause excessive brake lining wear, and it may be necessary to resurface the drum braking surface.

If brake shoes are to be replaced, always refinish a grooved drum. A grooved drum, if used with a new shoe, will wear the shoe and make proper brake performance difficult to obtain.

If the brake shoes are slightly worn (but to be reused) and the drum is grooved, polish the drum with a fine emery cloth but do not refinish. Eliminating all grooves in the drum and smoothing the ridges on the shoe would require removal of too much metal and pad, while 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 enough metal should be removed to obtain a true, smooth braking surface.

If a drum will not true up when refinished to the maximum available inside diameter specification, the drum must be replaced.

If the inside diameter exceeds the maximum limits, proper heat dissipation will be adversely affected and may cause distortion of the drum.

Drum Inside Diameter (Maximum):

• | 2-Door: 222 mm (8.740 in)

• | 4-Door: 256 mm (10.07 in)

### Taper and Runout Checks

An out-of-round or improperly tapered drum makes accurate brake shoe adjustment impossible and is likely to cause the excessive wear of other parts of the brake mechanism due to its eccentric action. An out-of-round drum can also cause severe and irregular tire tread wear as well as 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. If the drum cannot be brought within specifications by refinishing, it must be replaced.

When measuring a drum for out-of-round, taper and wear, take 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 specifications, the drum must be replaced as improper stopping or pulsating brakes could result.

• | 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, they are balanced and weights are welded in place as required. Do not remove any of these weights. Balance of the drum can usually be checked on an off-vehicle balancer. An out-of-balance drum must be replaced.