Your vehicle’s air brakes protect your life. Therefore, you should know how to adjust them in case of an emergency. The process of adjustment can be completed in three steps: air brake inspection, air brake adjustment and air brake final safety check
Air Brake Inspection
Meticulous inspection of air brakes could save your life and the lives of others. You can quickly and easily inspect your air brakes by following a seven-step inspection technique.
Purposeful inspection requires knowledge of the parts and their functions. A brief synopsis of the parts, functions and relevant safety checks are outlined below:
Air Compressor – this pumps air into the storage tanks, check the belt for position and tightness. Check adjuster tension. Only tighten to adjust when the engine is off and if you have the technical expertise. Note that some vehicles are equipped with automatic adjusters. Do not adjust an automatic adjuster. See an expert.
Air Compressor Governor – for automated air pressure control between 100 and 125 psi.
Air storage tanks – to hold/retain compressed air. Excessive air leakage is a sign of malfunction and needs urgent attention.
Air tank drains – for oil and water drains.
Alcohol evaporator – to add alcohol to the system, as in anti-freeze.
Safety valve – automatic pressure control/excessive pressure cutout that should start and stop at the 100-125 psi readings respectively.
Brake pedals – to engage the brake system.
Foundation brakes – the brake drums need to be checked for cracks.
Application pressure gauge – applied brake pressure indicator. Check for the rate of pressure build up. Must reach 80 to 90 psi in 3 minutes at idling speed. If not, there‘s a problem.
Low air pressure warning – Under 60 pressure-drop indicator. Always check this and be sure it is functioning by, first, switching off the engine and then switching the engine back on. Depress and release the brake pedals and listen for an indicator noise. This warning device is the lifeline of the air brakes.
Stop light switch – warning to trailing vehicles.
Front Brake Limiting Valve – (of historical interest)
Spring brakes – measure the truck pressure. Should come on when the pressure drops to 20 psi.
Parking Brake Controls – used on slopes. Test to be sure they work by trying to move at a low speed with the parking brake engaged.
Antilocking brake system (ABS) – works together with the yellow malfunction lights.
Air Brake Adjustment
Using the manufacturer’s manual, find out the push-rod stroke specification of your car.
Locate the slack adjuster unit and adjust with the appropriate wrench.
Watch the S-cam as you turn the adjuster. Excessive movement indicates you are turning in the wrong direction; try the opposite direction.
Following the counter-clockwise direction, tighten until brake shoes fully press against the brake drums.
Measure the push-rod and confirm that it is less than 2 inches.
Air Brake Final Safety Checks
Because of the importance of air brakes, after you complete the adjustment, repeat the following steps:
Recheck the low pressure warning signal
Rebuild the air pressure to between 90 and 125 psi and recheck the safety cut out function on the safety valve.