Moving Truck Fire Traced to an Overheated Rear Brake, North Texas (2021)

A moving company asked us in 2021 to find out why one of its box trucks caught fire on a North Texas highway while running empty. No insurer or other investigator was involved, so we were free to take parts apart. The company is kept anonymous.

From the outside in

We examined the truck at the repair shop where it had been towed. The cab and the engine compartment had no fire damage, and the fluid levels were where they should be. The worst damage ran up the right side of the cargo box from the rear tires toward the cab, and the inner right rear tire had burned down to its steel belts. Under the box the plywood floor was charred. The exhaust system was in good condition, and the battery cables, though damaged by heat, showed no arcing.

Inside the box, the fuel load was plywood walls and flooring, plastic skylights and moving blankets. On the right wall a burn pattern rose from floor to ceiling above a gap between the floor and the wall. The patterns showed the fire entering the box from outside rather than starting within it.

Taking the wheel ends apart

A shop mechanic removed the outer right rear wheel so we could reach the inner dual and the brake. The upper brake shoe on that side was discolored by heat, and its lining had large heat cracks. On the left rear, the shoes were in good condition. The lining measured about 5/16 of an inch on both sides. We also reviewed the work summaries for the truck.

Where the fire began

The area of origin was the right rear dual wheels, and the point of origin was the right rear brake shoes. An overheating brake was the only competent ignition source we found, and it ignited the inner tire. From the tires the fire climbed the side of the box and burned into the plywood and blankets inside. We ruled out the electrical system and the exhaust as ignition sources. Overheated brakes are among the first things we check in vehicle fire investigations.