The Long Descent with Fading Brakes
You are driving a loaded 4-axle rigid tipper with a full air-brake system, grossing 31,000 kg, down a long mountain descent on a two-lane road. The descent is 8 km at an average 7% gradient. Your service brakes are in good condition and were adjusted two days ago. The vehicle has a retarder and an engine brake. About 2 km into the descent you notice the brake pedal travelling further before it bites, and the vehicle is no longer holding the set speed with the same pedal effort. The air pressure gauge still reads normal in both circuits. A light truck is 60 m behind you and closing. There is a runaway emergency escape lane signposted 3 km ahead. Your tachograph shows you have been driving for 3 hours 40 minutes since your last 45-minute break, and you have 1 hour 20 minutes of driving left before you reach your daily limit.
1. Diagnose what is happening and set out, in order, the actions you take in the next 60 seconds.
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Diagnosis. Normal air pressure with increasing pedal travel and loss of retardation is the classic signature of brake fade from heat, not an air leak. The drums and linings are overheating because the service brakes have been doing work that the retarder and engine brake should be doing. As linings heat, their friction coefficient falls and the pedal must travel further to generate the same retardation. This is progressive: if you keep relying on the service brakes, you will reach a point where no pedal effort stops the vehicle.
Actions, in order:
- Select a lower gear immediately - the lowest gear that will not over-rev the engine - and bring the retarder and engine brake to maximum. Use the service brakes only in short, hard applications to bring speed down, then release, rather than riding them.
- Reduce speed now, decisively, while you still have retardation. Target a speed at which engine braking alone holds the vehicle. Do not wait to see whether it recovers.
- Hazard lights on and, if safe, a brief brake-light signal to warn the truck behind, which is closing at 60 m and may not have seen your problem.
- Move right and hold your lane, keeping the escape lane option open. Do not overtake anything.
- Assess the escape lane. If speed is still climbing after step 1 and 2, commit to it early - an escape lane used at moderate speed is a controlled stop; used late it is a crash.
- Keep the engine running and in gear so you retain retarder, engine braking and steering assistance.
Driving hours are irrelevant to this decision. You do not stop on a live descent to manage a 45-minute break.
2. You reach the bottom safely. Explain what must be checked before you continue, and how this descent should have been driven from the top.
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Checks before continuing. Heat-related fade does not resolve the moment you stop - in fact, parking with hot brakes concentrates heat into the drums and can crack them or boil the fluid in any hydraulic circuit. So:
- Stop in a safe place and let the brakes cool with the vehicle free to roll slightly rather than holding it on hot brakes; use chocks or a flat surface.
- Inspect drums and linings for cracking, glazing, blueing and oil contamination; check for brake drag and for any wheel running hot.
- Check for air loss and for any signs of a seized or leaking component once cool.
- Record the defect and report it, even if nothing is found - a fade event is reportable information for the operator's maintenance records.
- Have the brakes function-checked before the next descent; if in any doubt, do not descend.
How it should have been driven.
- Gear and retarder selected before the descent began, not after the first sign of trouble. The correct gear is the one that holds the vehicle at a safe descent speed on engine braking alone.
- Brakes used in short, firm applications to shed speed, then released, so heat has time to dissipate - never continuous light pressure.
- Speed set low at the top and held there. Speed gained on a descent is very hard to recover.
- Escape lanes identified in advance as part of the route plan.
- Load and gradient respected: 31,000 kg on 8 km at 7% is a serious descent and deserves a lower entry speed than an empty vehicle.