Brake Drum: Service and Repair
STANDARD PROCEDURE - BRAKE DRUM MACHININGIf a brake drum is deeply scored or warped, it can be machined on a brake lathe equipped to machine brake drums. Follow the manufacturers instructions on the machining procedure.
Measure the brake drum inside diameter before machining. If machining the drum will cause the drum to exceed maximum allowable diameter, do not machine the brake drum. It needs to be replaced.
CAUTION: Do not machine the brake drum if it will cause the drum to exceed maximum allowable diameter.
All brake drums are marked with the maximum allowable brake drum inside diameter (Fig. 40).
When machining, make sure the final finish feed cut is set to fine in order to avoid a screw effect on the brake shoes when the brakes are applied. This final feed cut specification varies from lathe manufacturer to lathe manufacturer.
BRAKE DRUM
REMOVAL
1. Raise vehicle.
2. Remove rear tire and wheel assembly.
3. Slide brake drum off mounted wheel studs of hub and remove from vehicle (Fig. 41). If drum does not come off, further brake clearance can be obtained by backing off brake adjuster screw using following steps:
a) Fabricate pawl release tool like one shown using a coat hanger or heavy mechanics wire (Fig. 42).
b) Remove plug from rear of support plate below wheel cylinder.
c) Insert fabricated tool through access hole in support plate, under adjuster, against lever pawl (Fig. 43). Pawl is attached to and pivots from leading shoe. When inserting tool through hole, directing tool somewhat forward (toward leading shoe) assures better contact with pawl.
d) While pushing on pawl with fabricated tool to disengage it from adjuster star-wheel teeth (Fig. 43), rotate star-wheel downward to back off adjustment using a small screwdriver or brake adjuster tool.
e) Once adjuster screw is backed off a sufficient amount, drum should slide off wheel studs.
f) Remove tools and reinstall plug in support plate.
INSTALLATION
NOTE: Before installing drum, inspect brake shoe linings for wear, alignment, and contamination. Repair or replace as necessary.
NOTE: If rust or any foreign material is present on hub, drum or wheel mating surfaces, wet wire brush these areas to remove prior to assembly of parts.
1. Properly remove any buildup formed along outer edge of drum's machined braking surface.
2. Adjust brake shoes to drum diameter using a brake shoe gauge.
3. Install brake drum on rear hub and bearing (Fig. 41).
4. Install tire and wheel assembly. Tighten wheel mounting nuts to 135 Nm (100 ft. lbs.) torque.
5. Lower vehicle.
6. Road test vehicle stopping in both forward and reverse directions. Automatic-adjuster will continue to adjust brakes as necessary during road test.