Meritor Hydraulic and Mechanical Drum Brakes Maintenance Manual 4H
This maintenance manual (MM4H) covers the service, repair, and adjustment of Meritor Hydraulic and Mechanical Drum Brakes, including the 13-inch and 15-inch Stopmaster models. These brakes utilize wedge-type actuators to provide balanced braking force through a dual-shoe system.
1. Key Technical Specifications
Proper brake performance relies on precise technical settings and wear monitoring:
- Brake Lining Thickness: Linings must be replaced when the material is worn down to 1/16-inch (1.5 mm) above the rivet heads.
- Drum Service Limits: Standard 15-inch drums have a maximum allowable diameter of 15.120 inches; if a drum is worn or machined beyond this limit, it must be replaced.
- Wedge Head Engagement: During assembly, the wedge head must be oriented so that the adjusting screw and solid plunger are correctly aligned with the leading and trailing shoes.
2. Core Maintenance Procedures
- Brake Adjustment: Automatic adjusters should not require manual intervention during operation; however, during initial installation, the adjusting bolt is turned to bring the linings into contact with the drum and then backed off to provide proper clearance.
- Lubrication: Critical components, including the wedge head, plungers, and adjusting screws, must be lubricated with a Meritor-approved grease, such as Mobilith SHC 460, during every major overhaul.
- Parts Preparation: Metal parts should be cleaned with a safe solvent (kerosene or diesel fuel) and dried with rags or compressed air, while linings must be kept entirely free of oil and grease.
3. Safety and Operational Warnings
- Asbestos/Non-Asbestos Dust: Users are cautioned not to use compressed air or dry brushing to clean brake assemblies, as airborne dust—regardless of material type—can cause serious health problems.
- Actuator Precautions: Never apply air or hydraulic pressure to an actuator while it is disassembled, as internal components can be ejected with high force, causing injury.