What causes automatic slack adjusters to fail?

Root Causes of Automatic Slack Adjuster Failure

1. Contamination and Foreign Object Intrusion
Dust/Mud Accumulation: In construction machinery or mining vehicles, when the adjuster seal fails, hard particles can infiltrate the ratchet or screw mechanism, causing wear or seizure.
Grease Contamination: Poor-quality grease or grease mixed with metal shavings creates an abrasive paste effect, accelerating abnormal wear of the internal friction pair.

2. Corrosion and Chemical Attack
Salt Spray/Deicing Agents: In coastal or winter road environments, the adjuster housing can rust and perforate, and internal springs or bearings can break due to chloride ion corrosion.
Brake Fluid/Oil Leakage: The seals of hydraulic adjusters swell with incompatible fluids and fail, leading to pressure leaks or piston seizure.

3. Mechanical Overload and Shock
Brake Overload: Frequent sudden braking causes the adjuster push rod to experience impact forces far exceeding the design value, cracking the internal ratchet teeth or deforming the threads.
Improper Installation: Misalignment of the adjuster and brake chamber push rod. Continuous lateral forces can cause uneven bearing wear or housing cracking.

4. Lubrication Failure
Dry Friction: After long-lasting lubricant evaporates or loses at high temperatures, metal parts come into direct contact and rub, resulting in abnormally high-temperature adhesion (such as sintering of the screw and nut).
Incorrect Lubrication: Injecting grease into non-lubricated points (such as certain self-sealing bearings) can damage the original protective design.

5. Material Fatigue and Aging
Spring Fracture: Under high-cycle loads, a return spring that has exhausted its fatigue life suddenly breaks, causing the adjuster to lose its compensation capability.
Plastic Embrittlement: Nylon gears or clutch plates become brittle and crack after prolonged UV exposure or alternating hot and cold temperatures.

6. Design or Manufacturing Defects
Out-of-Control Tolerances: The meshing clearance between the ratchet and pawl is too large or too small, leading to premature wear or intermittent gear slippage.
Inadequate Heat Treatment: Inadequate surface hardness of key components (such as the screw) can cause threads to collapse and deform during repeated adjustments.

7. Human Factors Due to Improper Maintenance
Forced Manual Adjustment: Unauthorized manual adjustment of the adjustment bolt disrupts the preset compensation logic, resulting in subsequent malfunctions. Improper assembly: Omitting thrust washers or retaining rings after overhaul can cause axial movement and failure of internal mechanisms.

8. Temperature Extremes
High-temperature conduction during braking: During long downhill descents in mountainous areas, heat from the brake drum is transferred to the adjuster, causing carbonization of grease or hardening of seals.
Freezing: In environments below -30°C, condensed water can freeze inside the mechanism, locking moving parts.