Air brakes are the most important safety system on a semi truck and trailer. When something goes wrong, it is not a problem to put off until next week. For owner-operators and fleets running out of Vancouver, Burnaby, Surrey, Delta, Langley, Coquitlam, Abbotsford and Mission, knowing the early warning signs can prevent a dangerous situation and a long, expensive breakdown.
This guide covers the most common semi truck air brake problems, what causes them and when to call a mechanic.
How Truck Air Brakes Work, in Brief
An engine-driven air compressor builds air pressure, a governor controls when it builds and stops, and an air dryer removes moisture before the air is stored in the tanks. When the driver presses the brake pedal, air flows through valves and lines to the brake chambers, which push the slack adjusters and apply the brakes. Spring brakes act as parking and emergency brakes and apply automatically if air pressure drops too low.
Because the whole system depends on holding air, small leaks and worn parts quickly affect braking performance.
Warning Signs of Air Brake Problems
- Low air pressure warning light or buzzer coming on
- Air pressure building slowly after start-up
- Air pressure dropping fast when parked with the engine off
- Hissing sounds from lines, fittings, gladhands or chambers
- Brakes dragging, overheating or smelling hot
- Truck pulling to one side when braking
- Longer stopping distances or a soft, unusual pedal feel
- Spring brakes applying on their own while driving
- Water or oil found when draining the air tanks
If the low air warning comes on while driving, stop safely as soon as you can. Do not keep driving with a system that cannot hold pressure.
Common Causes of Air Brake Problems
Air Leaks
Leaks are the most common air brake problem. They can come from cracked or rubbed air lines, loose fittings, worn gladhand seals between the truck and trailer, leaking valves or a damaged brake chamber diaphragm. Many leaks can be heard when the system is fully charged and the engine is off.
Compressor, Governor and Air Dryer Problems
A worn compressor, a faulty governor or a clogged air dryer can cause slow pressure build-up, pressure that will not stay in range, or moisture and oil in the tanks. Moisture in the system can damage valves and freeze in cold weather.
Brakes Out of Adjustment
When slack adjusters, pushrods or brake components wear, the brakes can go out of adjustment. This means longer stopping distances and uneven braking. Brakes that keep going out of adjustment usually point to a worn part that needs replacing, not just another adjustment.
Brake Chamber and Spring Brake Problems
A leaking service diaphragm, a damaged chamber or a failing spring brake can cause leaks, dragging or brakes that do not release fully.
Worn Brake Components
Worn shoes, pads, drums or rotors, along with damaged camshafts, bushings or return springs, all reduce braking performance and can cause noise, pulling or overheating.
Do Not Ignore Small Air Brake Problems
A slow leak or a brake slightly out of adjustment might not seem urgent, but air brake problems get worse and can lead to failed inspections, roadside out-of-service orders and, most importantly, unsafe braking. Fixing a leaking fitting or chamber early is far cheaper than dealing with a breakdown on the highway.
Simple Checks Drivers Can Do
- Do a proper air brake check as part of every pre-trip inspection
- Listen for leaks with the system fully charged and the engine off
- Watch how quickly air pressure builds after start-up
- Drain the air tanks regularly, or check that automatic drain valves are working
- Inspect gladhand seals, air lines and chambers for damage
- Report any warning light, pulling or dragging right away
Can Air Brakes Be Repaired at the Roadside?
In many cases, yes. A mobile semi truck and trailer mechanic can find and fix air leaks, replace air lines, fittings, gladhand seals, valves and brake chambers, check and adjust brakes and replace slack adjusters at your yard or on the roadside. If the problem is hard to pin down, mobile diagnostics can help find the real cause, including ABS faults.
Mobile Air Brake Repair Across Metro Vancouver
Solid Heavy Truck & Equipment Repair repairs air brakes on semi trucks, trailers, dump trucks and fleet trucks across Vancouver, Burnaby, Surrey, Delta, Langley, Coquitlam, Abbotsford, Mission and all of Metro Vancouver, 7 days a week from 8 AM to 11 PM.
Air brake problem? Call (778) 955-3113 or request a free quote.
