Most trucks on the road today contain drum brakes powered by compressed air. Drum brakes offer reliable and effective results. Yet as time goes on, drum brakes experience a lot of wear and tear. Improperly maintained brakes accumulate such wear and tear much more quickly than they should, hastening the rate of component failure.
The drums, in particular, often succumb to premature failure as the result of maladjusted components. To make matters more complicated, a wide variety of underlying issues may affect the rate of drum brake wear. If you would like to boost your knowledge of truck brake troubleshooting, keep reading. This article investigates three factors that can lead to premature drum wear.
- Worn Camshaft Bushings
- Faulty Relay Valve
One of the most important components in a drum brake goes by the name of the brake cam. This S-shaped piece of metal attaches to the end of the camshaft,and remains in constant contact with the cam rollers attached to the two brake shoes. When you release the brakes, the camshaft rotates so that the skinny part of the cam touches the cam rollers.
When you depress your brake pedal, the camshaft rotates so that it contacts the cam rollers in its wide orientation. This pushes the cam rollers outward,causing the brake shoes to contact the drum and create the friction necessary for stopping.
As the intermediary between the brake pedal and the brake cam, the camshaft experiences a lot of stress over time. This stress tends to wear out the secondary component known as the camshaft bushing, which provides flexible support to the camshaft. As the bushing wear, they allow more and more non-rotational movement into the camshaft.
Technicians refer to this movement as radial play. If the radial play of a camshaft exceeds 0.030 inches, then the bushing has likely reached the end of its lifespan. At that point, the radial play causes the brake cam to exert different amounts of pressure on each of the cam rollers. As a result, the brake shoes do not contact the drum equally.
This uneven contact has several negative repercussions. For one thing, the brake shoes wear down unevenly. For another, the camshaft experiences a greater amount of stress, potentially causing it to fail as well. Finally, the poor contact causes the drum to develop uneven wear patterns.
If the radial play becomes too severe, one of the brake shoes may even remain in constant contact with the drum’s surface. This leads to the problem known as brake drag, which causes your engine to work harder, while also overheating the drum and brake shoes. For the absolute best braking, try to keep radial play no greater than 0.010 inches.
Premature brake drum wear may also stem from issues with your truck’s air system. In particular, faulty relay valves often lie behind excessive or uneven drum wear. There lay valve acts as an intermediary between the foot valve and the brakes at the rear of your truck, making up for the phenomenon known as brake lag.
Brake lag occurs as a result of the especially long distance between the front and rear brakes on a truck. If only one valve controlled the air going to both front and rear brakes, the rear brakes would engage noticeably after the front brakes,creating unsafe braking conditions. There lay valve ensures that air reaches all of your truck’s brakes at virtually the same time
A faulty relay valve creates serious problems when it comes to braking safely. In addition, a bad relay valve can exacerbate drum wear. In some cases,a bad relay valve fails to release air pressure when you lift your foot from the brake. As a result, the rear brake shoes remain in contact with the drum.
In other words, a faulty relay valve also contributes to brake drag, and can lead to premature drum failure.
For more information about keeping your brakes in tip-top shape, contact the truck and brake professionals at Godfrey Brake Service &Supply.