Determining when it’s necessary to schedule brake maintenance has less to do with how many miles you drive than with what the nature of that driving is. For instance, a local delivery truck making dozens of stops each day will obviously wear down brakes much more quickly than an over-the-road driver making stops only three times per day.
Or do they? The surprise element in this equation is heat. While a waste management truck making multiple stops in a single minute can run its brakes at a temperature of 450 degrees, that of an over-the-road truck may average only 125 degrees. Low temperatures like these can wear out shoe linings in just a couple of months, with drums needing replacements every three times the shoes are changed.
Here is a quick checklist you can use to see if it’s time for brake maintenance:
Check S-cam Brakes’ Slack Adjusters: After parking on level ground and chocking the wheels, turn off the parking brakes to allow movement in the slack adjusters. If you can move the slack adjuster more than an inch where it’s attached to the push rod, you need an adjustment. A truck built after 1994 will have automatic slack adjusters, but they still need checking. When the pushrod stroke has exceeded the legal brake adjustment limit, you need a repair. It can be tempting to make a manual adjustment, but that is simply masking a deeper mechanical problem.
Examine Brake Drums, Linings and Hoses: Check your brake drums to ensure they don’t have cracks longer than one-half the width of the drum’s friction area. Be sure that the linings are not loose or soaked with lubricant, and check to be sure they are not dangerously thin. Check air hoses for spots where they could be cut or worn.
Check Low Pressure Warning Alert: Turn the engine off when you have adequate pressure, then turn the electrical power on, stepping on and off the brake pedal to reduce pressure. Ensure that the warning signal activates before the pressure drops to below 60 psi. If the signal does not work, have your truck serviced.
Test Spring Brakes: Fan the air pressure to reduce pressure in the tank, and the tractor protection valve and parking brake valve should close if it’s a tractor-trailer combination. The parking brake valve should close on single vehicles and other combinations when pressure falls below 20-40 psi.
Monitor Air Pressure Buildup: When in operation, the pressure should increase within 45 seconds from 85 to 100 psi in a dual air system vehicle. If this is not occurring, you should not drive until the truck has been serviced.
Measure Air Leakage: Turn off your engine, fully-charge system at 125 psi, then release the parking break to time the air pressure rate. The loss rate shouldn’t be over 2 psi per minute in a single vehicle, and below 3 psi for a combination vehicle. Then, with the brake pedal, apply 90 psi or more, watching the initial pressure drop. If it’s more than 3 psi for a single vehicle, or 4 psi for combination vehicles, your air loss rate is too high.
Check Cut-in and Cut-out Pressures on Air Compressor Governor: When running your engine at a fast idle, the air compressor should be cut-out by the air governor at around 125 psi, and the air pressure should stop rising. While the engine is still idling, pump the brakes to reduce air pressure, and the compressor should cut-in at the manufacturer’s cut-in pressure.
Check the Parking Brake: Stop your truck, then put the parking brake on. Put your vehicle in a low gear and test that the parking brake holds.
Check Service Brakes: At normal air pressure, move the vehicle forward slowly and then apply the brakes firmly, taking note of any pulling to a particular side or unusual response in your vehicle. This test helps you identify problems you may not notice while driving on the road. It can be challenging to know when to take your truck in for brake maintenance or repair, but your safety and the safety of others depends on high-performing brakes. And if you’re in the Lincoln, Nebraska, area or the Lexington, South Carolina, area, stop by Gray Diesel & Equipment Services to get your brakes in good, working order.