Braking on Downgrades and Emergency Braking
Before the downgrade
- Check the brakes at the top of the hill by applying them firmly while still at speed. If they do not hold, stop and find out why before descending.
- Choose a gear low enough that engine braking holds your speed; a common rule is the same gear you would need to climb the grade.
- Set a safe speed before you start down and stay under it.
Snub braking
Apply the brakes firmly enough to drop about 5 mph, then release and let the engine brake hold the lower speed. Repeat as needed. This lets the drums cool between applications and keeps the vehicle controlled. Do not ride the brakes down a long grade: heat causes brake fade, and overheated drums can stop working altogether.
Emergency braking
Above about 20 mph, use stab braking: apply all the way, release the moment the wheels lock, and reapply as soon as they roll. Below 20 mph, use controlled braking, which is firm pressure without locking the wheels. With ABS, apply firm steady pressure and steer.
If the brakes fail
Downshift, use the parking brake gradually (applying it fully at speed can lock the wheels and cause a skid), and look for an escape ramp. Use the ramp rather than ride it out.
Worked example
On a 6 percent grade with a loaded trailer, the pedal starts to feel soft at 45 mph. You release the brakes, downshift two gears, and the engine brake holds 30 mph. If speed still climbs, take the escape ramp; continuing to apply the service brakes only adds heat.
Traps
Do not say an engine brake replaces the service brakes, do not use the spring brake as a normal hill-holding tool, and do not stab the brakes at low speed.