What are some common brake camshaft failures?

Brake camshaft, as a core component of truck braking system, operates under high load and high friction conditions for a long time, and many kinds of failures may occur.

Brake camshaft, as a core component of truck braking system, operates under high load and high friction conditions for a long time, and many kinds of failures may occur. The following is a detailed analysis of its common failures and their causes and effects: 
Camshaft Wear Failure 
1. Abnormal wear on cam surface 
Manifestation: grooves, scratches or uneven wear on camshaft working surface, and craters may be formed in serious cases.
Cause: 
The clearance between the brake shoes and camshaft is too small, resulting in increased dry friction.
Insufficient lubrication (e.g., deteriorated lubricant, clogged oil circuit) and lack of protection for the friction surface.
Dust, metal shavings and other impurities enter the brake drum, forming abrasive wear.
Impact: Uneven pushing force of brake shoes, resulting in reduced braking force, and the vehicle may experience braking run-off.
2. Journal wear 
Performance: The diameter of the camshaft and bushing journal parts becomes smaller, and the fit clearance increases.
Reason: 
Insufficient wear resistance of the bushing material or coaxial deviation during installation.
Long-term high-frequency braking leads to overheating of the journal and bushing friction.
Impact: camshaft operation generated by shaking, brake shoe action lag, brake response time is extended.
Camshaft Deformation Failure 
1. Bending Deformation 
Manifestation: The axis of the camshaft deviates from a straight line, which may lead to brake shoe stagnation or movement interference.
Cause: 
Instantaneous excessive impact during braking (e.g. emergency braking).
Uneven tightening torque of bolts during installation, resulting in imbalance of force on the shaft.
The vehicle is overloaded for a long time and the braking system is overloaded.
Impact: The brake shoes cannot open normally, the braking force decreases greatly, and even causes brake failure.
2. Deformation of the cam profile 
Manifestation: The eccentric profile of the cam changes its shape (e.g., the degree of ellipticity exceeds the standard).
Causes: 
Material fatigue (metal lattice distortion after long-term high-frequency use).
High temperature annealing (loss of material hardness due to brake overheating).
Impact: irregular brake shoe travel, braking force suddenly large and small, the vehicle may produce violent shaking when braking.
Failure of connection parts 
1. Loose or broken bolts 
Performance: Loose or broken bolts connecting the camshaft with the drive shaft and brake arm.
Reason: 
The bolts are not tightened according to the specified torque during installation, or the bolts are loosened due to vibration during use.
Insufficient strength of the bolt material, fatigue fracture after prolonged exposure to alternating loads.
Impact: Camshaft and brake system transmission disconnection, brake function completely failed.
2. Worn splines/keyway 
Manifestation: Wear and slippage of the spline teeth or keyway connecting the camshaft to the drive shaft.
Cause: 
Frequent braking causes repeated shocks to the transmission torque.
Excessive spline clearance and concentrated contact stress.
Impact: Reduced power transmission efficiency during braking, delayed or weakened braking force.
Lubrication System Failure 
1. Oil line blockage 
Performance: The lubricant cannot reach the camshaft friction surface, and there is dry grinding locally.
Cause: 
Excessive impurities in the lubricant are deposited in the oil passage.
The rubber sealing ring is aging and falling off, blocking the oil circuit.
Impact: accelerates the camshaft wear, and in serious cases, may cause locking and stalling.
2. Oil seal failure 
Manifestation: oil leakage from camshaft end seal, lubricant penetration into the brake drum.
Cause: 
The oil seal is aged, hardened or scratched during installation.
The camshaft axial movement is large, the oil seal lip wear.
Impact: Lubricant contamination of the brake drum and brake shoes, resulting in reduced friction and longer braking distance.
Abnormal Noise Failure 
1. Friction noise 
Performance: “squeak” “click” sound when braking.
Cause: 
The camshaft surface is poorly lubricated and rubs directly against the brake shoe pins.
Metal shavings from wear are trapped between the friction surfaces.
Impact: Although it does not affect the braking function temporarily, but it indicates that the parts are abnormal and need to be overhauled in time. 2.
2. Impact noise 
Manifestation: “clunking” sound when the vehicle is traveling or braking.
Reason: 
camshaft and bushing clearance is too large, when running to produce shaking impact.
Loose connecting parts, such as camshaft fixing nut loose.
Impact: It may aggravate the damage to the parts, or even cause the camshaft to fall off.
VI. Comprehensive faults related to braking performance 
1. Uneven braking force 
Manifestation: Difference in braking force between left and right wheels of the same axle exceeds the standard (e.g. more than 15%).
Reason: 
The camshafts of the left and right wheels are not worn to the same degree.
Deformation of the camshaft on one side leads to insufficient opening of the brake shoes.
Impact: The vehicle will run to one side when braking, which may lead to loss of control at high speeds.
2. Braking drag 
Performance: After releasing the brake pedal, the brake shoes do not fully return to their original position and there is continuous resistance at the wheels.
Cause: 
The camshaft is not flexible (e.g. deformed, rusted), resulting in delayed resetting of the brake shoes.
Stuck camshaft and brake shoe contact area (e.g. foreign object embedded).
EFFECT: Overheating of brake drums, increased tire wear, and increased vehicle fuel consumption.