Brake Fade on a 7% Descent
You are driving a 40-foot coach with 44 passengers down a signed 7% grade that runs for 6 km on a two-lane highway in northern Ontario. The road is wet and the outside temperature is 4°C. Your bus has an automatic transmission with a retarder, ABS, and air brakes. You entered the grade at 85 km/h in high range with the retarder set to its lowest setting. After 2 km you notice a hot-brake smell, the service brake pedal feels softer and travels farther, and the bus has crept up to 95 km/h despite light continuous brake application. The air pressure gauge still reads 105 psi. A sign at the top of the grade warned trucks to use low gear. Your next safe pull-off is 800 m ahead. Passengers are chatting and do not notice the change.
1. What hazard is developing, and what should you do in the next few seconds?
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The hazard is brake fade from continuous light brake application on a long grade. The brakes are overheating, which explains the hot smell, the softer and longer pedal, and the speed creep despite braking. Wet pavement also reduces traction and increases stopping distance.
Immediately increase the retarder to its highest setting, manually select a lower gear, and use firm brake applications followed by release rather than riding the brakes. Turn on hazard lights, keep both hands on the wheel, and aim for the pull-off 800 m ahead. Avoid sudden steering or hard braking that could cause a skid. Tell passengers to stay seated. The air pressure is still normal, so this is not yet a low-air problem; the priority is reducing speed and allowing the brakes to cool before they fail further.
2. What was wrong with the descent setup, and what is the correct technique for a long 7% grade?
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The setup was wrong in three ways: you entered the grade too fast, remained in high range, and left the retarder on its lowest setting. A 7% grade for 6 km should be treated as a serious descent, especially wet.
The correct technique is to slow down before the grade begins, select a low gear that will hold a safe speed without continual service braking, and set the retarder to a high setting. Use intermittent firm brake applications to bring speed down, then release, letting the brakes cool between applications. Do not ride the pedal continuously. Use pull-offs to check brake temperature and allow cooling, and keep speed low enough that a stop could be made safely. The warning sign at the top was a cue to change the setup before entering the grade, not after symptoms appear.
3. If the pedal goes to the floor and the retarder fails while speed climbs to 110 km/h, what is your plan?
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Prioritize steering and warning others. Keep both hands on the wheel, turn on hazard lights, sound the horn, and look immediately for an escape ramp, a wide shoulder, or an uphill pull-off. Do not shut off the engine. Manually select the lowest available range to use whatever engine braking remains, and use the retarder if any function returns.
If service brakes are gone, the spring brakes may eventually apply as air pressure drops, but that can lock the rear wheels, so be ready for a sudden stop and keep the bus straight. If an escape ramp is available, use it. If not, use the safest available terrain or shoulder to scrub speed gradually rather than striking a fixed object at high speed. Warn passengers loudly to brace themselves. After stopping, secure the bus, evacuate if there is any fire risk, and call 911 and dispatch.