Caravan brakes are probably the least talked about – most important thing on a caravan. Most of the time we usually trust the caravan manufacturer, and take what they give us. The rest is handled by the caravan dealer, who usually organizes the car trailer plug wiring, and installs a brake controller in the car. They give a brief on how to use it, and what it does. And off we go to enjoy our first trip in our brand new caravan.
It is usually only when we encounter our first scary skid, sway or god forbid – a jack-knife, that we sit down and actually do some research on what the hell happened. It doesn’t take a college degree to figure out that the incident, probably had something to do with the brakes. Slamming on the brakes in a hairy situation is usually the what we would have been doing just before everything went south.
There are a lot of factors that are involved when considering towing a caravan safely. However being able to slow down or stop when the moment calls for it is probably the most important thing. Braking technology in automobiles has progressed a lot over the last few decades. Most new cars come standard with disc brakes and some sort of safety brake control feature like ABS (Anti-lock Braking System).
Caravan brake systems however, are still governed by cost rather than safety. Most manufacturers prefer the standard Electric Drum Brakes. They are easy to fit, low cos and easy to wire up and control. In this article we will be elaborating on various types of caravan brakes and the differences between them. But first we will look at the legal requirements for caravan brakes.
All brakes that are fitted to trailers and caravans in Australia are required to comply with Australian Design Rules No. 38. The ADR’s in this section are mainly used by brake manufacturers to calculate appropriate braking forces required for various ratings. The most relevant rule to caravan manufacturers, and DIY modifiers is the classification of the trailers based on their weight and the type of braking required for each weight class. The Vehicle Standards Bulletin for Building Trailers specifies three distinct categories:
The most standard of all caravan brake types the drum brake relies on friction of the braking shoes, on the inside of a drum to provide the stopping power. The entire braking assembly is housed in a cylindrical metal casing or drum.
A typical drum brake assembly consists of:
Drum brakes are due to the following advantages:
The main disadvantage of drum brakes is the brake fade (reduction in braking force) caused due to over heating. The drum brakes rely on the efficient contact of the shoes with the inner surface of the drum. Over long periods of continuous use the brake drums can heat up quite significantly. This causes the drum to expand – and since it is circular the only way it expands is outward. This reduces the contact between the drum and the shoe, causing a reduction in braking. At high temperatures the properties of the brake shoe lining also change, causing less friction and hence less braking.
Depending on how the actuator arm is activated, there are two types of drum brakes.
In mechanical drum brakes the actuator arm is made to move mechanically via steel cables. When pulled tight the steel cables cause the actuator to pivot and the braking shoes to engage the drum. Mechanical drum brakes are only used on trailers that weigh less than 200kg when fully loaded. The brakes are actuated via an over-ride coupling.
When the towing vehicle brakes the coupling pushes against the ball attached to the vehicle. This moves the coupling in and out of a override cylinder. This motion tightens the cables causing the actuator arm within the drum to engage the brakes.
Electric drum brakes are the stock standard brakes fitted to most caravans with loaded weight above 2000kg. By law they are required to be able to control the braking force form inside the tow vehicle. This is achieved via a braking controller mounted on the tow vehicle dash. The braking controller controls the current to the brakes and allows the tow vehicle brake pedal to talk to the caravan brakes via the trailer plug. Electric drum brakes are highly popular because of their quick braking response compared to the mechanical variant. The motion of the actuator arm is achieved by movement of an electromagnet attached to its end.
When the brakes are activated in the tow vehicle – an electric current is sent via the trailer plug to the electromagnet in the drums. The current charges the magnet and magnetizes it causing it to move outward towards the metal drum due to magnetic attraction. This in turn pivots the actuator arm which activates the brakes.
When a caravan travels offroad or over corrugations for long periods of time, the metal to metal connections within the drum brakes can face severe damage. Due to the constant rattling over one another the connection and joints can wear and damage over time greatly reducing braking efficiency. To overcome this brake manufacturers release off-road versions of their brakes with rubber bushings and grommets that prevent wear due to metal to metal contact and rattling.
Due to the fact that it uses electricity to initiate and control braking response, electric drum brakes are not used for marine and extreme off-road (creek crossing) applications.
Disc brakes have proven their performance – being widely used in the competitive motorsport since the 1950’s. Braking is achieved by using a calliper with pistons that pushes friction pads against a rotating disc attached to the wheel. The motion of the piston is achieved using hydraulic fluid such as the typical DOT brake fluids used in a car braking system.
A typical disc brake assembly consists of:
Disc brakes have many advantages over drum brakes:
The main disadvantage with disc brakes is the cost. They are fairly expensive compared to a similar set of drum brakes. It is also more difficult to incorporate the parking handbrake, especially in electric over hydraulic brake types. Another problem is that the actuator usually requires some position to be mounted on the outside of the caravan. Drum brakes don’t have this hassle to deal with.
Mechanically actuated disc brakes are actuated using a hydraulic over-ride coupling. Since braking cannot be independently controlled by the driver in the car, here again the maximum weight limit on the trailer or caravan is 2000kg.
The master cylinder is located above the coupling. As the coupling moves in and out, the master cylinder piston is compressed and braking is achieved. The handbrake manually compressed the master cylinder to act as a parking brake when required.
These disc brakes are used on all trailers above 2000kg GTM. They can be controlled via dash-mounted brake controller similar to electric drum brakes. They have an actuator that converts the electric signal from the braking car into hydraulic response in the master cylinder. The actuator can come at ratings up to 1600PSI, for really strong braking power when needed. The ALKO iQ7 Offroad braking system uses compressed air to compress the hydraulic fluid during braking to achieve a better response. The compressed ait is maintained by an on-board compressor and is stored with the hydraulic fluid in a reservoir tank.