Surface Finish
Whenever you remove brake drums, thoroughly clean and inspect the drums
for the following conditions:
Minor surface wear is normal and will not affect brake operation. However,
ensure that the inside diameter does not exceed the maximum specification.
Refer to Inside Diameter Check for more information.
A cracked drum is unsafe for further use. Do not attempt to weld a cracked
drum. Always replace a cracked drum. Refer to
Brake Drum Replacement
.
Smooth any light scores using a fine emery cloth. Heavy or excessive
scoring will cause excessive brake lining wear. Resurface the drum braking
surface, as necessary, if the brake shoe lining is excessively worn. Refer
to
Brake Drum Refinishing
.
If you are replacing the brake shoes, always refinish a drum with deep
grooves. A drum with deep grooves, if used with new brake shoes, will wear
the brake shoe lining and adversely affect brake performance. Refer to
Brake Drum Refinishing
.
If you are not replacing the brake shoes and the drum is grooved, polish
the drum using a fine emery cloth. Do not refinish the drum. Eliminating
all of the grooves in the drum and smoothing the ridges on the brake shoe
lining requires the removal of too much metal and lining. If left alone,
the grooves in the drum and ridges on the brake shoe lining match and you
may obtain satisfactory brake performance.
Inside Diameter Check
| • |
Before refinishing a drum, measure the
inside diameter. Ensure that the maximum inside diameter of the drum does
not exceed 222 mm (8.74 in). |
| • | If the inside diameter exceeds maximum limits, the proper heat
dissipation will be adversely affected and may cause distortion of the drum. |
| • | During refinishing, only remove enough metal in order to obtain
a true, smooth braking surface. Refer to
Brake Drum Refinishing
. |
| • | If you refinished the drum to the maximum allowable inside diameter
specification and you did not obtain a true, smooth braking surface, replace
the drum. Refer to
Brake Drum Replacement
. |
Taper and Runout Checks
An out-of-round or improperly tapered drum may cause the following conditions:
| • | Inaccurate brake shoe adjustment |
| • | Excessive wear of other parts due to its eccentric action |
| • | Irregular tire tread wear |
| • | A pulsating brake pedal |
When measuring a drum for out-of-round, taper, and wear, complete the
measurements at the following locations:
| • | The open and closed edges of the machined surface |
| • | At right angles to each other |
Runout is a low spot in the roundness of a drum. If runout exceeds the
maximum specification, replace the drum. 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) |
When the drum exceeds the specification limits for out-of-round and/or
taper, refinish the drum in order to obtain a true, smooth braking surface.
Refer to
Brake Drum Refinishing
.
If you refinished the drum to the maximum allowable inside diameter
specification and the drum exceeds the specification limits for out-of-round
and/or taper, replace the drum. Refer to
Brake Drum Replacement
.
Balance
Brake drums are balanced during manufacturing by welding weights on
the drum, as required.
Do not remove any of these weights.
Inspect the balance of the drum on an off-vehicle balancer. Replace
an out-of-balance drum. Refer to
Brake Drum Replacement
.
