Brake Shoe

A brake shoe is the friction element of the air brake system that presses against the wheel to slow the car. It is the wearing part that actually contacts the wheel and turns the car's motion into heat.

Where It Sits

Brake shoes attach to the heads of the brake beams in the truck. Each shoe is held in a shoe head and is positioned so that its curved face matches the tread of the wheel. When the brakes are not applied the shoe stands just clear of the wheel; when they are applied the brake rigging, driven by the air brake cylinder, forces the shoe firmly against the rotating tread.

What It Does

As the shoe is pressed to the wheel, friction between the shoe face and the wheel tread retards the wheel and brings the car to a stop. The shoe is intended to be the sacrificial part of that contact, wearing away over time so that the much more valuable wheel is preserved. Shoes are made of materials chosen for their friction characteristics and wear rate, and the friction also conditions the wheel tread.

Wear and Inspection

Because it does the rubbing, the brake shoe wears and must be replaced when it reaches its wear limit; a shoe worn too thin, broken, or out of position no longer brakes effectively. Worn and defective shoes are routine inspection findings, and the minimum thickness and condemnable conditions are set by the AAR interchange rules and field manual.