Disc Brakes

Travel trailers have utilized electrically-operated drum braking systems for many years. But today, some RVers are considering upgrading to disc brakes. But is retrofitting disc brakes to an existing trailer worth the expense? To answer this question, it is important to understand how brake systems work.

As a vehicle moves down the road, it develops a tremendous amount of stored energy in the form of inertia (the tendency to keep it moving). To stop the vehicle, the brakes use friction to convert this kinetic (moving) energy into heat. In the case of drum brakes, an electrical impulse from the tow vehicle actuates an electro-magnet against the face of the brake drum. As the wheel rotates, the magnet moves a lever, causing the shoes to be forced against the rotating surface of the drum.

The heat built up from the friction of this contact dissipates the kinetic energy, but also causes the brake drum to expand from the heat developed in long downhill runs. As the drum expands, it moves slightly away from the brake shoes and we experience classic brake fade. Electrically operated brakes have always been a clunky kind of affair. If not properly adjusted, the tow vehicle experiences a sudden jolt as the brakes start to grab. When the trailer comes to a stop, there may be no more rotational force to push the shoes against the drum, leaving us with no braking action after a stop. If you were stopped at a traffic light on a hill, the tow vehicle's brakes would have to hold the entire load of trailer and tow vehicle in position.

We have become accustomed to disc brakes on modern cars and trucks. The main components of a disc brake are the brake pads, the caliper which contains a piston, and the rotor, which is mounted to the hub of the wheel.

Disc brakes are more effective than drums in stopping a vehicle, since the pads are pushed by greater hydraulic pressure against each side of a rotor. When you push your foot against the brake pedal, the hydraulic fluid pushes the piston so that the pads are forced against the surface of the rotor. The heat developed by the friction is now dissipated into the surrounding air by the cooling vents in the rotor. As the rotor expands due to heat absorption, it does not move the pads away, and as a result we do not experience brake fade as can occur with drum systems.

When you remove your foot from the pedal, the rubber dust seal exerts just enough pressure to pull the piston back and the pads move away from the rotor.

Disc brakes for trailers operate with high hydraulic pressure developed by a 12-volt pump mounted in the trailer. The pump receives a signal from the standard electric brake controller in the cab of your tow vehicle to know how much pressure you need to be able to stop. Some disc brake systems have a slight delay before the pressure builds sufficiently in the brake lines. Systems that build the pressure faster will mean better and smoother braking.

Some aftermarket disc braking systems require up to two full seconds before recognizing the brake signal, and then another two seconds or so to build up the pressure to apply the brakes. Because disc brake systems have higher pressures pushing the pistons and pads against the rotors, they stop trailers in a shorter distance than drum brakes.

When drum brake shoes wear down, the drum may get scored and may need to be refaced before replacing the shoes.
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