Drum Brake System: Testing and Inspection

WARNING: Brake assembly dust and dirt should not be removed by either blowing off with an air gun or vacuuming with a standard industrial vacuum cleaner because a health hazard from breathing in asbestos dust may develop. Also, any machining done on brake linings or pads should be done using proper exhaust-ventilated equipment.

NOTE: Removal of dust and dirt from brake assemblies should be done by using the Rotunda Brake and Clutch Service Vacuum 091-00001 or Rotunda Brake Parts Washer 065-00016 or an equivalent.

INSPECTION
1. Use Rotunda Brake/Clutch/Service Vacuum 091-R0001 or equivalent to remove all dust from backing plates and interior of brake drums (1126).
2. Inspect the following components of the brake system:

Wheel Cylinders
1. Rear wheel cylinders should not be disassembled unless they are leaking. Pull back each rear wheel cylinder dust boot and inspect for leakage.
2. Excessive brake fluid at this point indicates leakage past the piston cups and a need for rear wheel cylinder (2261) overhaul. A slight amount of fluid is nearly always present and acts as a lubricant for the pistons. If evidence of leakage is noted, the rear wheel cylinder should be disassembled, inspected and overhauled.
3. Inspect the rear wheel cylinder bore for scratches and pitting. If the rear wheel cylinder is pitted or has deep scratches, the rear wheel cylinder must be replaced.

Brake Drums
1. A brake drum should be visually inspected and measured with Rotunda Brake Drum Micrometer 104-00046 or equivalent. Before making an inspection or measurement, remove grease, brake fluid, or other contaminants from the brake drum using denatured alcohol.
2. Best shop practice requires measuring every brake drum with a brake drum micrometer regardless of visual inspection. The brake drum micrometer is set to the drum diameter and measures the amount and type of wear. Measure the diameter at various points 45-degrees apart around the brake shoe and lining contact area, and at the bottom of the deepest groove to determine if the brake drum requires replacement.

Brake Lining
1. Inspect rear brake shoes and linings (2200) for excessive lining wear or shoe damage. If lining is damaged or worn within 0.79mm (1/32 inch) of the rivet heads on riveted linings, it must be replaced. Replace any rear brake shoe and lining that has been contaminated with oil, grease or brake fluid. Replace rear brake shoe and lining in axle sets only. Never replace just one rear brake shoe and lining of a brake assembly. Replace both primary and secondary shoes. Prior to replacement of lining, brake drum diameter should be checked to determine that brake drum diameter is within specification. If braking surface diameter exceeds specification, the brake drum must be replaced.
2. Check condition of rear brake shoes and linings, retracting spring, hold-down springs, and brake drum for signs of overheating. If rear brake shoe and lining metal parts have a slight blue coloring, indicating overheating, retracting and hold-down springs should be replaced. Overheated springs lose their tension and could allow new rear brake shoe and lining to drag and wear prematurely, if not replaced.





Springs
1. Check springs for:
^ Spread or collapsed coils
^ Twisted, bent or damaged shanks
^ Discoloration -- This is a sign of brake overheating. Overheated springs lose some of their tension and should be replaced.

Backing plate
1. Inspect the brake backing plate for correct mounting and securely tightened mounting nuts. Torque to 34-47 Nm (25-35 ft lb)
2. Inspect the brake shoe and lining contact pads (where the brake shoe and lining rests).
^ Deep grooves in the brake shoe and lining contact pads could restrict brake shoe and lining movement.
^ If grooves exist, hand sand the brake shoe and lining contact pads.
^ If the grooves are still present after hand sanding, the backing plates must be replaced. Any attempts to remove the grooves by grinding may result in improper brake shoe and lining to brake drum contact.
3. Inspect all other brake parts and replace any that are worn or damaged.