Sparesbox Blog

How do Brake Shoes Work?

By James Andrew

Wed Oct 07 2015

Brake Shoes Explained

Brake Shoes are a major component of the Drum Brake System, one of the earliest braking systems to appear in automobiles. A Drum Brake is simply a large metal barrel or “Drum” that rotates with the wheel as part of the hub assembly. When you apply pressure to the brake pedal, hydraulic cylinders or pistons force the Brake Shoes (which sit internal to the drum) against the inner surface of the drum, creating friction and therefore slowing the vehicle. Brake Shoes often serve multiple purposes, not only as the main brakes, but as the vehicles handbrake as well. Vehicles often have a cable attached to one of the Shoes, which is levered by the handbrake within the car. Even nowadays a Drum Brake is often used within the conventional Disc Brake to act as the handbrake.

 

Drum Brake Mechanism

 

Contrary to popular belief, Drum Brakes are very effective due to their “self energising” action. As the first edge of the Brake Shoe is pushed into the spinning drum, the downward motion pulls the rest of the shoes surface against the drum. For this reason almost all Brake Shoes have what is known as a leading and a trailing edge, where the liner material is closer to the edge of the backing plate on one end than the other. This needs to be observed when replacing your Brake Shoes.

 

Left Rear Brakes

 

Drum Brakes vs. Disc Brakes

 

The achilles heel of the Drum Brake is its heat retention. The thick metal drum and shoes retain an enormous amount of heat, and with little to no airflow over the operating parts, they cool slowly. This is one big disadvantage in motorsport that lead to the eventual rise of the Disc Brake.

 

The other disadvantage is maintenance. While a conventional Disc Brake is self adjusting, Drum Brakes require adjusting to remain even. As the proximity of the shoe-to-drum can be adjusted on each corner, incorrect adjustment can lead to the car pulling left or right when braking. Uneven wear due to leaking cylinders or broken adjusters can lead to uneven adjustment and an ineffective handbrake. Similar to Disc Brakes, as Drum Brakes wear they leave behind a dust. This dust is allowed to collect within a Drum Brake causing harshness and noise.

 

How Brake Fit Together

 

Can I replace my Brake Shoes myself?

 

The replacement of Brake Shoes can be very tricky and tedious depending on your car. Your first time changing them will likely end in many curse words and throwing of spanners. They rely on a series of pins and high tensile springs to operate correctly, all of which need to go back exactly as they came out and with the correct adjustment. If you do decide to give it a go, leave yourself plenty of time. If you can get the assistance of a friend who has done it before we highly recommend it! Always wear goggles and hand protection, as the springs can be merciless when (and they will if you’re inexperienced) they fly off in any which direction at 100 miles per hour. Always do one side at a time so if you get stuck you have another side to reference. And just incase you can’t remember how the Brake Shoe went together, it pays to take a photo beforehand.