Whenever brake drums are removed, they should be thoroughly cleaned and inspected
to see if the drums are cracked, scored, deeply grooved, or beyond the specified out-of-round
limit.
| • | A cracked drum is unsafe for further service and must be replaced. Do
not attempt to weld a cracked drum. Smooth out any slight scores. |
| • | Heavy or extensive scoring will cause excessive brake lining wear and
may require refinishing the drum braking surface. |
| • | If the brake linings are slightly worn but are still reusable and the
drum is grooved, polish the drum with a fine emery cloth but do not refinish it. Eliminating
all grooves in the drum and smoothing the ridges on the lining removes too much metal
and lining. If left alone, the grooves and ridges match, and satisfactory service
can be obtained. If the brake linings need to be replaced, refinish a grooved drum.
A grooved drum, used with a new lining, will not only wear the lining, but also will
make it difficult, if not impossible to, obtain proper brake performance. |
| • | An out-of-round drum makes accurate brake shoe adjustment impossible and
is likely to cause excessive wear of other parts of the brake mechanism. An out-of-round
drum can also cause service and irregular tire tread wear, as well as a pulsating
brake pedal. |
| • | The extent to which a drum is worn or out-of-round can be measured accurately
with an inside micrometer fitted with the proper extension rods. When measuring a
drum for wear or the extent to which it is out-of-round, take measurements from the
inside edge to the outside edge of the machined surface at 90-degree intervals
around the circumference of the drum. |
| | When the drum exceeds the specified
out-of-round limit, refinish the drum. |
Inspect the brake drum as follows:
- Inspect the drum for cracks or damage.
- Measure the inside diameter.
Specification
The inside diameter wear limit value is 231 mm
(9.1 in).
- Replace the drum, if the measured value is over the
limit, or if the defect is found.
