Brake Fade on the Descent with a Load Shift
You drive a 3-axle tractor unit with a 3-axle semi-trailer, gross combination mass 40 t, carrying steel coils. The coils were loaded by the shipper and secured with two web straps over the top; you did not check the lashing points because the shipper said it was done. On a 6 km descent at 6 %, your brake pedal has begun to travel further and the vehicle pulls to the right under braking. The trailer's ABS warning lamp has illuminated. You smell hot brake lining. Halfway down there is a lay-by on the right and a steep escape lane is signposted 1.5 km further on. Traffic behind is close.
1. Explain what is happening mechanically and what your immediate actions must be.
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The symptoms point to brake fade combined with an ABS fault and a load-securing problem.
- Longer pedal travel and a hot lining smell indicate overheating brakes: the friction material is losing effectiveness (fade) and the brake fluid may be approaching boiling, which can let the pedal go to the floor.
- Pulling to the right suggests uneven braking between sides, consistent with one side overheating more or a seized component.
- The trailer ABS lamp means the trailer's anti-lock system is not functioning, so a hard application may lock trailer wheels and jack-knife the combination.
- Two straps over steel coils on a 40 t combination is almost certainly inadequate; if the coils shift under braking, the load can move forward and destabilise the outfit.
Immediate actions:
- Do not brake harder. Select a low gear and use engine braking and the retarder if fitted to hold a steady low speed.
- Use the brakes in short, firm applications with recovery intervals rather than continuous light pressure, so they can cool.
- Put on hazard warning lamps and, if safe, allow the close traffic behind to pass.
- Take the lay-by on the right, stop, chock the wheels, and let the brakes cool before inspecting. Do not pour water on hot drums or discs.
- If you cannot stop safely, use the escape lane rather than continuing to the bottom.
2. After stopping, how do you assess and correct the load securing before continuing, and what do you record?
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Assessment:
- Identify the coil mass and dimensions from the consignment note. Steel coils are dense; a single coil can weigh several tonnes and, unrestrained, will move forward under braking with enough force to penetrate the cab.
- Check that each coil is individually restrained, not merely covered by straps. Coils should be laid in a purpose-built cradle or chocked, with the axis across the vehicle or in a well, and secured with rated chains or straps to the vehicle's lashing points, with edge protection where straps cross steel.
- Verify the straps: check for cuts, fraying, and the label rating. A typical 50 mm strap may be rated around 2,500 daN lashing capacity; compare the total lashing capacity with the load mass and the applicable securing standard. Two straps are unlikely to meet the requirement for a multi-tonne coil.
- Check the lashing points on the trailer for deformation and confirm the trailer floor and headboard are sound.
Correction: do not move until the load is properly secured. If the correct equipment or cradle is not available, arrange for it or transship the load.
Record: note the defect in the vehicle/load defect log, photograph the original securing, inform the operator and the shipper in writing that the load as presented was not adequately secured, and note the ABS fault and brake condition for the workshop. Report the ABS fault and brake overheating as defects requiring repair before the vehicle is used again.