Brake Repair and Replacement Raleigh Triangle
With large vehicles, brake maintenance is extremely important. The most important aspect of brake service is the duty cycle of the vehicle. A long-haul semi may use the brakes a few times each day while the local garbage truck may be hitting the brakes 200-300 times each work day. Heavy duty use of a vehicle’s brakes could result in the brake shoes being replaced every other month and the drums 2-3 times each year. Over-the-road trucks may be able to stretch their brake shoe replacement to the 250,000 miles mark.
With Brakes, Weather Makes all the Difference
Winter weather can have a big difference in the health and life of brakes in heavy equipment. In colder climates, the use of salt and de-icing chemicals such as magnesium chloride can reduce the life of brake parts. These chemicals can get into tight spaces and cause corrosion, increasing the need for maintenance. Trailers that have been sitting a while with these chemicals on their brake parts can cause the brakes to freeze, with the worst case being the truck actually dragging the trailer’s tires. Washing the underside of trucks is a good preventive measure. Also, installing manufacturer’s suggested parts will go a long way to keeping your brakes healthy.
Types of Truck and Trailer Brakes
While the laws about auxiliary brake systems can vary from state to state, most require any trailer weighing more than 3000 pounds to have their own braking system. Most brake systems for trailers fall into three distinct categories: Electric, surge and air brakes.
Electric Brakes
Electric Brakes work off the electromagnetic principle. With an electric magnet, the more voltage you run through it the stronger the magnet you get. Power is supplied by the pulling truck’s batteries. When the brake is applied, the brake shoes are pulled to the iron brake drum by the electromagnet attached to it. The stronger the voltage that is applied, the more friction applied by the brake shoes to the drum, creating greater braking force.
Trailers fitted with electric brakes require a standalone battery supply in case the trailer breaks away from the pulling truck. In a breakaway, there would be no power going to the trailer from the pulling truck and so the standalone battery is available. A breakaway cable is attached to the trailer and in the event of a breakaway maximum breaking force is applied to the breaks.
Hydraulic Surge Brakes
Hydraulic surge brakes, commonly called just surge brakes, are typically found on smaller trailers or submergible trailers, like those for boats or any other area where an electrical short or lack of enough power can cause brake failure. They work very similar to car brakes. In surge brakes, there is a spring with connected to a master cylinder. When the cylinder is depressed, pressure on the brake fluid increases causing the brakes to engage. The higher the pressure the more force that is applied to the brakes. The pressurized fluid is equally distributed to each brake via a network of brake lines throughout the chassis.
Air Brakes
Air brakes are the most often used in large vehicles and trailers. They work by using air to depress the shoes into the drum. Air brakes are preferred to other forms of brakes due to ease of connection to the main vehicle. The air for the system is applied by the air compressor off the engine the of the vehicle.
Air Brakes in trailers are the only type of brake that will actually stop the vehicle in the event of a leak or a failure. Air Brakes on trailers are always depressed (full braking force) in the rest position. The application of air to the system actually releases the brakes and allows the trailer to move. In the event of a breakaway the trailer would immediately apply the brakes and attempt to stop the trailer.y
Maintenance of Brakes
Brake failure is a common cause of accidents for tractor trailers. Many parts within the brake’s system are designed to be regularly replaced, including the pads, shoes, drum, springs, pins and bushings. Brake shoes have indicators built in to show when the brake pads need to be replaced. Not replacing these parts can cause serious safety issues.
Lubrication is another important part of the overall maintenance. Slack adjusters, both manual and automatic, both require proper lubrication to work well. Also, in the brakes the S Cams need to be properly lubed to allow them to work as intended. The S cam pushes the brake shoes into the drum, stopping the vehicle.
Lines, hoses and air gauges are very important parts of the overall system. All hoses should be checked for cracks and the air pressure should ideally be between 100 psi and 125 psi. Anything less than 60 psi will prevent the trailer brakes from releasing.