Applicable Systems
Street Crane Overhead Crane
Symptoms
The hoist brake fails to hold the load when the motor stops. The load drifts downward, indicating brake engagement failure.
Possible Causes
- Brake disc or shoe worn beyond the minimum thickness
- Brake actuator (pneumatic, hydraulic, or electromagnetic) not developing sufficient force
- Brake spring fatigued, reducing the clamping force
- Oil or grease contamination on the brake friction surfaces
Troubleshooting Steps
- Step 1: Measure the brake disc or shoe thickness and compare to the minimum specification
Replace if below the minimum thickness stamped on the component - Step 2: Check the brake actuator: air pressure, hydraulic pressure, or coil voltage
Repair or replace if the actuator does not achieve the rated force - Step 3: Inspect the brake friction surfaces for oil or grease contamination
Clean with solvent; replace the friction material if saturated - Step 4: Measure the brake spring free length and compare to the specification
Replace springs that have taken a set (shortened)
How to Reset
Reset: After brake repair or replacement, perform a load test with a test weight to verify the brake holds 125% of rated load before returning to service.
Common Replacement Parts
- Brake disc: OEM-specified, match to hoist model (Replace at minimum thickness)
- Brake friction material: Asbestos-free, OEM-specified (Replace in matched sets)
- Brake spring: Die-spring type, match to OEM spec (Replace in sets)
Frequently Asked Questions
- Q: How often should crane brakes be inspected?
Daily before operation: visual check. Monthly: functional test. Annually: disassembly, measurement, and load test.
- Q: What is the brake holding test?
Lift a test load, stop the hoist, and verify the load does not drift. Then test with 125% of rated load for new installations or after major repairs.
- Q: What causes brake failure?
Wear, contamination, spring fatigue, actuator failure, and thermal damage from excessive cycling. Regular inspection and maintenance prevent most failures.
Source: OEM Operation Manual
Category: Crane