What safety hazards can a worn truck camshaft cause?

Camshaft wear is a relatively common fault in truck braking system, if not dealt with in time, it will cause various threats to driving safety.

Camshaft wear is a relatively common fault in truck braking system, if not dealt with in time, it will cause various threats to driving safety. The following are the specific safety hazards it may cause and its mechanism of action: 
Decrease in braking force and prolongation of braking distance 
1. Directly affecting the braking efficiency 
Wear Principle: After the surface of the camshaft (especially the cam contour) is worn out, the “lift” of the camshaft that pushes the brake shoes to open up will be reduced. For example, the maximum lift of a normal cam is 12mm, but after wear it may drop to 10mm, resulting in a reduction of about 15-20% in the area where the brake shoe meets the drum.
Safety Hazard: Braking force is directly proportional to the friction area, and insufficient fitting area will reduce the braking force of the whole vehicle, and the braking distance at the same speed may be extended by 10%-30%. For example, when the original braking distance is 30 meters, it may increase to 39 meters after wear and tear, which is easy to cause rear-end accidents in emergency situations.
2. Uneven braking force leads to runaway 
Difference between left and right wheels: If the camshafts of left and right wheels are worn differently (e.g. left wheel is worn 0.5mm, right wheel is worn 1mm), it will lead to the difference in braking force between the two sides exceeding the safety standard (usually the difference is ≤15%).
Driving risk: the vehicle will shift to the side with large braking force when braking, especially when driving at high speed (e.g. above 60km/h), the deflection may lead to loss of control of the vehicle, or even run out of the lane or collide with other vehicles.
Chain risks caused by abnormalities in the braking system 
1. Brake shoe sticking and delayed reset 
Effect of journal wear: If the clearance between the camshaft journal and the bushing widens from the standard value of 0.05-0.1mm to more than 0.3mm, it will lead to camshaft wobbling and the brake shoe may be stuck in the half-open state.
Potential danger: 
When the brake pedal is released, the brake shoes are not fully returned to their original position and the wheels are continuously subjected to braking resistance, leading to a sharp rise in the temperature of the brake drums (up to 300°C or more), which may lead to cracking of the drums or corrosion of the brake shoe friction pads.
Prolonged stalling will make the tire abnormal wear, tread temperature rises, increasing the risk of tire blowout.
2. Lubrication failure aggravates component damage 
The vicious cycle of wear and lubrication: metal fragments generated by camshaft surface wear will be mixed into the lubricating oil, forming abrasive wear and further aggravating the damage to journals and bushings. When the lubricant is heavily contaminated, this can lead to camshaft seizure (e.g., a truck with a worn camshaft that was not serviced in time ended up with a camshaft seizure on a mountainous downhill slope, leading to braking failure).
Chain consequences: the moment of clutching will produce a huge impact, which may lead to brake arm fracture, drive shaft deformation, and even make the whole braking system fail.
High-risk scenarios under special working conditions 
1. Downhill braking failure in mountainous areas 
The fatal effect of wear and tear: In continuous downhill sections, trucks need to use the brakes frequently, and the worn camshafts may be deformed due to thermal fatigue, resulting in a drastic reduction of braking power. For example, a heavy-duty truck lost braking power due to a worn camshaft on a long downhill grade and crashed into the refuge lane.
Risk mechanism: After the camshaft is worn, the speed and strength of the brake shoe opening decreases, which can not offset the gravity force of the vehicle in time, resulting in loss of control of the vehicle speed.
2. Wet road braking side-slip 
The amplification effect of uneven braking force: In rainy days or icy and snowy roads, the tire adhesion itself is lower, if the left and right wheel braking force is uneven due to the wear of the camshaft, the vehicle is more prone to side-slip or tailgate. Experimental data show that when the difference in braking force is more than 10%, the probability of skidding on wet roads increases by 2-3 times.
Hidden Safety Hazards and Increased Maintenance Costs 
1. Accelerated Wear and Tear of Other Components 
Indirect Effects of Wear and Tear: Abnormal wear and tear of the camshaft will change the balance of forces in the braking system, resulting in additional stresses on the brake shoe pins, return springs and other components. For example, a truck with untreated camshaft wear had its brake shoe return springs replaced 3 times in a row within 6 months, increasing maintenance costs by about $2,000.
Safety Hazard: Early failure of other components may cause brake failure at an unknown moment, increasing driving uncertainty.
2. Brake failure caused by high temperature 
Relationship between wear and heat dissipation: Wear of camshaft leads to poor fit of brake shoes, and the heat generated by friction during braking can not be evenly distributed, and the local temperature may exceed 400℃, resulting in thermal failure of brake shoe friction pads (coefficient of friction decreases by more than 30%).
Case in point: In a logistics truck, the right rear brake drum overheated and the friction pads failed due to camshaft wear during the hot summer months, and the truck failed to stop in time at an intersection and collided with a lateral vehicle.