Brake Fade on a Wet Mountain Grade
You are driving a 40-foot coach with 42 passengers and a gross weight of 36,500 pounds down a 6% grade that is 5 miles long. The pavement is wet, and the posted speed for heavy vehicles is 35 mph; the general limit is 55 mph. At the summit, your speed is 58 mph. The coach has an automatic transmission with a retarder and a 'use lower gear' sign for vehicles over 26,000 pounds. You enter the grade in drive, with the retarder on its middle setting. After 1.5 miles, you have used the service brakes almost continuously to hold 55-60 mph. The pedal now feels low and spongy, you smell hot brake lining, and the speed has crept to 64 mph despite the retarder. Traffic is light behind you, and a narrow dirt pullout is about 300 feet ahead.
1. Identify the driving errors that led to this situation and explain what should have been done at the summit.
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The errors began before the grade. Entering a 6% downgrade at 58 mph in drive ignored the heavy-vehicle speed and the lower-gear sign. A 36,500-lb coach at that speed carries far more energy than the brakes can absorb over 5 miles. The retarder was only on its middle setting, so the service brakes had to do most of the work.
At the summit the driver should have:
- Slowed to the posted 35 mph or lower before the grade began.
- Selected a low gear-generally the same gear that would be needed to climb the grade-so engine braking held speed.
- Set the retarder to a high setting and tested the brakes at low speed before committing.
- Used controlled snubs: apply the brakes firmly to reduce speed, release, and let speed build only to a safe limit. Continuous light application overheats drums and pads.
- Checked the wet-road traction limit and kept extra space ahead.
Once the pedal went low and hot lining was smelled, the driver was already in brake fade. The correct response is not to keep pressing harder and hope; it is to reduce speed immediately using lower gear and retarder, then stop at the first safe place.
2. What immediate actions do you take now, and what do you do once stopped?
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Immediately: keep both hands on the wheel, apply a firm, steady brake application to get speed down, shift to a lower gear, turn the retarder to maximum, and turn on hazard flashers. Do not use the parking brake at highway speed; it can lock the rear wheels or damage the driveline. Aim for the pullout 300 feet ahead, but do not turn sharply at speed with passengers aboard.
If the coach will not slow enough for the pullout, look for a runaway ramp or a wider escape area. Do not continue down the grade hoping the brakes recover. If you must stop on the road, stop as far right as possible, keep hazard flashers on, and get passengers to a safe location away from traffic if there is fire risk or the coach is blocking the lane.
Once stopped in the pullout: set the parking brake, place the transmission in Park, and let the brakes cool. Do not pour water on hot brakes. Inspect for fluid leaks, damaged drums or hoses, and pedal firmness. Smelling hot lining and a low pedal mean the coach should not continue until inspected and repaired. Notify dispatch, arrange another coach or a mechanic, and document the incident.