Fleet managers in the United States must make sure their trucks are safe to drive, or they can face serious legal consequences. Although you need to thoroughly check your trucks on a scheduled basis, some parts are more liable to wear than others and must therefore receive closer attention. Brake shoes are a vital part of a truck's ability to stop safely in an emergency, so it's crucial that you spot and deal with any of the early signs of damage or wear. Find out how rust-jacking can affect a truck's brake shoes, and learn more about the steps you need to take to guarantee the vehicle is fit to drive.
How brake shoes work
Truck manufacturers have used brake shoes for several decades, and these vital components are a core part of any drum brake system. When a truck driver brakes, a wheel cylinder forces the brake shoes out and against the system's spinning drums. This process creates friction, which slows the drum and brings the vehicle to a halt.
Brake shoes are curved steel parts that manufacturers coat with a material that increases friction on one side. This makes the part work more efficiently when the driver activates the brakes. If the brake shoes don't work as effectively as they should, the truck will skid, which could result in disaster.
The problem of rust-jacking
When a truck driver brakes, the brake lining can move fractionally away from the brake shoe. This can happen due to the sudden extreme temperature that the friction causes and/or because of fine particles from the road getting in between the two parts. Ongoing movement every time the truck driver brakes can slowly wear away the special layer on the brake shoe.
In turn, this process (micro-abrasion) can expose the bare metal of the brake shoe. Water and grime from the road surface can then quickly touch the bare metal, triggering the surface to oxidize and form rust. Layers of rust can gradually build up between the shoe and the brake lining. Eventually, the lining could crack, which could seriously impair the truck's ability to brake safely.
Signs to look for
Certain signs strongly indicate that you have a problem with rust-jacking. Common characteristics include:
- You have at least 1/8" of usable brake lining remaining above the rivet heads.
- The lining buckles between the rivet heads, leaving a gap between the shoe and the lining block.
- Visible cracks run horizontally across the lining and along the edge of the lining block.
Certain trucks are more susceptible to the problem. For example, trucks that regularly drive in wet or damp conditions are obviously more likely to experience the issue. Exposure to sea water or salt and chemical compounds used to de-ice road surfaces can also accelerate the process.
Perhaps less obviously, trucks that cover less mileage can become more vulnerable because the shoes don't need to work so often. In turn, this allows rust to develop more quickly and to a greater extent. The quality of the brake parts also makes a difference. Many brake shoes now include stronger, thicker layers of paint that are better able to resist micro-abrasion.
If you see the signs of rust-jacking, you don't actually have to throw away old shoes every time. If the damage isn't too bad, it's possible to remanufacture the shoe to replace the worn layer.
If you're replacing parts, make sure you use high-quality brake shoes that can cope with the demands you place on your fleet. Talk to your supplier about new developments in brake shoe technology, such as special coatings and manufacturing processes that can extend the life of these vital parts.
Of course, prevention is generally better than cure, so it's important to take steps to prolong the life of existing shoes. Regularly spray the truck's undercarriage to wash away salt and grime deposits. Don't blast the truck with a pressure washer. Use a gentle hose instead, or you may damage other vulnerable parts of the truck.
If there's a problem with your trucks' brake shoes, you could run into serious trouble. Make sure your mechanic, someone like Godfrey Brake Service & Supply, knows which signs to look for.