Brake Fade on a Loaded Tanker Descent
At 03:30 you are driving Tanker 9, a 2,000-gallon tanker with about 1,500 gallons on board (three-quarter full, baffled), grossing near 54,000 lb, on a 6 percent downgrade that runs 1.5 miles to a stop-sign intersection. The posted limit is 45 mph. You entered the grade at 40 mph in a low gear with the engine brake on high. Halfway down, speed has crept to 52 mph despite the engine brake; the service brake pedal initially held well but now needs noticeably more travel, and the truck is not slowing as expected. You smell hot brake lining. The tank baffles are working, the road is dry, and a passenger car is tailgating about 50 ft behind.
1. What should have been done before the descent, and what do the current symptoms indicate?
Read the worked answer
Before the descent:
- Perform a brake check and a snub test at the top, where there is room to stop if something is wrong.
- Select a gear low enough that the engine brake and compression hold the load without service brakes, generally the same gear used to climb the grade.
- Set a target speed at or below the posted limit, and know where the escape ramp is.
- Confirm the tank baffles are intact and the load is not free to surge.
What the symptoms mean:
- Speed creeping up despite the engine brake plus a hot-lining smell plus a pedal that needs more travel is the signature of overheated, fading brakes. The drums and linings are hot enough that friction is dropping off.
- Distinguish this from an air loss: an air problem typically gives a soft or spongy pedal and a low-pressure warning, not a burning smell. Fade gives a pedal that may still feel firm while the truck simply does not slow.
The descent is already in trouble; the response has to be immediate and decisive.
2. What are your immediate actions, in order?
Read the worked answer
- Stop feeding the fade. Get off the service brakes so they can cool; continuous application is what created the heat.
- Downshift to a lower gear to raise engine braking, if the current speed allows it without over-revving. Do it early rather than after the speed climbs further.
- Use the engine brake and firm, short brake applications rather than light continuous pressure, and keep the speed down between applications.
- Look for the escape ramp or a safe pull-off. If speed continues to climb and braking is not recovering, commit to the ramp. A gravel arrester bed is designed for exactly this and is a far better outcome than a 54,000-lb truck entering a stop-sign intersection at speed.
- Do not pump the brakes and do not rely on the spring brakes as a service brake at speed; they apply only the rear and can lock wheels.
- Communicate: notify dispatch and the incident commander that the tanker is out of service and where you are stopping.
Regarding the tailgater: do not brake-check. Signal early, and let them deal with their own following distance.
3. The escape ramp is 600 ft ahead on the right, you are at 55 mph, and the truck is still slowly accelerating. What do you do, and what do you tell dispatch?
Read the worked answer
Take the ramp.
600 ft at 55 mph is roughly 7 seconds. That is enough time to commit if the decision is made now and not after another attempt to save the descent. The alternatives are worse: continue and arrive at the stop-sign intersection with fading brakes, or attempt a hard stop that overheats the brakes further and may not hold.
Execution:
- Signal, move to the ramp entrance, and keep the steering straight; do not straddle the edge or brake hard at the entrance.
- Enter at a controlled speed, keep the wheels rolling into the arrester bed, and let it stop the truck.
- Expect the load to shift forward and the truck to nose down; the baffles help but the surge will be felt.
To dispatch: your location, direction, that the tanker is in the escape ramp with brake fade, no injuries known, and that the ramp and the road at the bottom need to be considered for closure or traffic control. Request a mechanic and a second tanker. The apparatus does not leave the ramp until the brakes are inspected and the cause is understood.