Brake fade and a soft pedal on a long descent
You are driving a loaded minibus down a long mountain descent with a series of bends. The vehicle is fully loaded with 14 passengers and luggage. About two-thirds of the way down, you notice the brake pedal feels spongy and travels further before biting, and the vehicle is not slowing as sharply as before even with firm pressure. You can smell a hot, acrid odour. Your speed has crept up to about 60 km/h on a section signed for 40 km/h. There is a lay-by about 150 m ahead on the right. The engine is running normally and the steering feels fine.
1. What is happening, and what is your immediate plan?
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Diagnosis: the symptoms - spongy, longer-travel pedal, reduced braking force despite firm pressure, and a hot acrid smell on a long descent with a heavy load - point to brake fade (overheated brake linings/discs) and possibly boiling brake fluid producing gas in the lines. Both reduce braking effectiveness exactly when you need it most.
Immediate plan:
- Stop braking continuously - continuous dragging is what caused the heat. Use engine braking by selecting a lower gear to hold speed, which takes the load off the brakes and lets them cool.
- Aim for the lay-by 150 m ahead and stop there safely. Do not continue the descent on fading brakes.
- Warn following traffic - hazard lights, and a light brake application to show you are slowing.
- Once stopped, let the brakes cool. Do not pour water on hot discs/drums - thermal shock can crack them. Do not immediately set off again.
Key point: a loaded vehicle on a descent needs engine braking, not riding the pedal. The fade is a warning that the brakes were being overworked.
2. After cooling, how should you drive the rest of the descent, and what should you check before continuing?
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Before continuing:
- Check the brake fluid level (a low level or dark fluid suggests a leak or overheating) and look for leaks at the wheels.
- Test the pedal: it should feel firm with normal travel. If it is still spongy or long, do not continue - get the brakes inspected.
- Check for a burning smell that persists, and look at the wheels for excessive heat or fluid weeping.
Driving the rest of the descent:
- Select a low gear before the descent begins so engine braking holds the speed; use the brakes in short, firm applications rather than continuous light pressure.
- Keep speed well below the signed limit given the load - 40 km/h signed means treat it as a maximum, not a target, with 14 passengers aboard.
- Leave a large gap ahead so you rarely need to brake hard, and use the bends to scrub speed gently.
- Stop periodically on long descents to let the brakes cool if the descent is very long.
Safety principle: with passengers aboard, a brake problem is a stop-and-fix problem, not something to manage on the move.