Brake Drum: Testing and Inspection

With the drum off the vehicle, measure the drum for diameter variation (oval shape). The diameter variation of the drum braking surface must not exceed either 0.0635 mm (0.0025 inch) in 30° or 0.0889 mm (0.0035 inch) in 360°.

Measure brake drum runout. Brake drum runout should be checked with the drum mounted on a brake lathe. Brake drum runout should not exceed 0.1524 mm (0.006 inch).

If either of these measurements are not within specification, reface or replace the drum.

Brake Drum Maximum Diameter Identification:

Always replace the drum if machining will cause the diameter to exceed drum maximum diameter. All brake drums are marked with the maximum allowable brake drum diameter.

DRUM BRAKE AUTOMATIC ADJUSTER

Adjuster Access Hose Plug:

Accessing The Automatic Adjuster:

Place the vehicle on a frame contact hoist with a helper in the driver's seat to apply the brakes. Raise the vehicle. Remove the adjuster access hole plug, from the rear brake support plate. This will allow access to the star wheel on the automatic adjuster mechanism. Then, to eliminate the possibility of maximum adjustment, insert a small screwdriver through the access hole in the support plate and back off the adjuster star wheel approximately 10 notches. It will be necessary to hold the adjuster lever away from the star wheel to perform this adjustment procedure.

Fully apply the brake pedal which will cause the brake shoes to leave the anchor. Upon application of the brake pedal, the adjuster lever should move downward, turning the star wheel on the adjuster. Thus, a definite rotation of the adjuster star wheel can be observed if the automatic adjuster is working properly. If one or more adjusters do not function properly, the respective brake drum must be removed for servicing of the adjuster mechanism.