Emergency Stops and Brake Failure Procedures
If service brakes fail
- Keep steering control; downshift progressively to use engine compression.
- Apply the parking brake gradually, not in one hard yank, to avoid locking wheels or damaging the mechanism.
- Look for an escape ramp, runaway truck lane, or flat off-road area.
- If air pressure is low, spring brakes will apply automatically at 20–45 psi; do not fight them.
- Do not pump air brakes when pressure is lost; pumping uses remaining air and does not restore a failed circuit.
Emergency stop with working brakes
Apply firm, continuous pressure; with ABS, hold the pedal and steer. If the vehicle has no ABS and wheels lock, release just enough to regain steering, then reapply. After any emergency stop, check for air loss, brake damage, and load shift before moving.
Worked example
A truck's low-pressure warning activates at 60 psi on a downgrade and the service brake pedal feels weak. The driver downshifts, moves to the shoulder, and applies the parking brake gradually. The spring brakes apply as pressure falls. The driver does not continue to the next exit; the correct decision is to stop as soon as it is safe. At 60 psi the warning has met the requirement, but the system is already at the safe-operating limit.
Traps
Waiting for zero pressure is dangerous. Using the parking brake as a hard emergency brake at highway speed can cause a skid. Pumping the pedal wastes air. Continuing after a warning because the pedal still feels a little firm is a serious error.
After the stop
Secure the vehicle, chock wheels, and do not move until the air system and brakes have been checked and the fault is corrected.