Drum brakes versus disc brakes, brake controllers and sway systems — your caravan brakes can enhance safety well beyond regular stopping. John Hughes tells us everything there is to know about brakes.
Braking systems are among the most critical components for all vehicles on the road, from bicycles to road trains. In this article, we look at various aspects of caravan brakes including the pros and cons of drum versus disc brakes and how they are actuated. We explore various types of brake controllers from basic through to the latest iterations. Finally, we cover additional systems that utilise your brakes to enhance safety, including breakaway devices and stability control.
Why does a caravan need brakes?
A caravan adds a lot of mass to a tow rig. If a caravan does not have its own brakes, then the tow vehicle must provide the braking force to slow down the caravan as well as the car. The reality is, cars are not designed to cope with this extra load. An unbraked caravan will dramatically increase rig stopping distances, have the potential to push the tow rig around and cause the tow vehicle brake system to fail due to overheating.
That’s why we have laws governing caravan brakes. Any trailer with a gross trailer mass (GTM) of more than 750kg must be fitted with brakes. Between 751kg and 2000kg GTM, brakes must be fitted to at least one axle of the trailer. Theoretically, a sub-2000kg tandem axle van may have brakes fitted to just one axle. In reality, though, most caravan manufacturers fit brakes on both axles for extra stopping power. For any caravan with a GTM of more than 2000kg, every wheel on both axles must be braked.
Electric drum vs hydraulic disc brakes
Most Australian caravans have electric drum brakes at each wheel. This system is dated, but it’s proven, cost-effective and reliable. Inside each wheel’s drum is a pair of brake shoes and an electromagnet. When you press the tow vehicle’s brakes, an electrical signal flows through the trailer plug to each drum magnet. The magnet, mounted on an actuating arm, becomes energised and is attracted to the spinning steel inner face of the drum. As the magnet grabs the drum surface, it pulls the actuating arm, forcing the brake shoes outward until they press against the drum’s interior.
Brake shoes spread out to force the brake pads onto the drum
This design has some clever aspects. Drum brakes are self-energising — as the shoes contact the rotating drum, they are dragged further into the drum, multiplying the braking force. A relatively small magnet and arm can thus produce significant stopping power. Brake shoes also have a large friction contact area which helps distribute force and can make them very durable in normal use. The enclosed drum can keep out some mud and debris. Also, many drum brake assemblies can incorporate a mechanical handbrake linkage for parking.
However, drum brakes do have downsides. They tend to run hotter and don’t shed heat as efficiently as discs, which can lead to brake fade on long downhill runs. If water gets inside during a river crossing or driving in heavy rain, drum brakes can take longer to dry out and regain full effectiveness. Electric drum magnets also lose some performance at very high speeds where the magnets grab the drum less effectively. Offroad, the constant vibrations and dust can cause faster wear of components, and mud or sand that sneaks past the seals can affect braking until cleaned out.
A hydraulic disc brake actuator receives an electrical signal to activate the brakes
Disc brakes are the norm in modern passenger cars and many 4WDs. They are increasingly an option for caravans — especially in the offroad and premium segment. A disc brake uses a flat rotor (disc) attached to the wheel hub and a calliper that squeezes brake pads onto the rotor to create friction.
The initiation of the braking process is the same in both drum and disc brakes. An electrical signal is sent to the caravan brakes when the tow vehicle is braking or in some instances decelerating. The difference with disc brakes is that the signal is sent to an electric over hydraulic actuator (EOH). This is a hydraulic pump unit that creates hydraulic pressure to activate the brakes. EOH systems require constant electrical power to operate. We have seen vans with flat batteries fail to operate the actuator, rendering the caravan brakes inoperable. Also, your breakaway system must be wired into the EOH unit so it can trigger the pump during a breakaway event.
Generally, disc brakes deliver more consistent performance, shorter stopping distances, and superior fade resistance than an equivalent drum brake system. Less fade on extended steep descents increases safety. Drivers often report that disc brakes on a heavy van feel more responsive, with less of the grabbing or shudder that sometimes afflicts electric drums when they heat up. Additionally, disc brake callipers can be designed with dust seals and high-temperature components suited to harsh conditions.
Brake callipers squeeze the brake pads onto the disc
Unlike drums, disc brakes fling off water and mud readily, so they recover grip faster after a dunking. They also tend to be easier to inspect and maintain. Replacing disc brake pads is usually simpler than pulling apart drums to service shoes and magnets.
However, disc brakes are generally more expensive than drum assemblies, and the setup is more complex due to the hydraulic lines and actuator. Another consideration is hydraulic disc systems need a separate mechanical parking brake mechanism (or an always-pressurised actuator) to hold a trailer at rest.
Disc brakes are growing in popularity in high end vans
Old-school override brakes
While a rarity these days, override brakes were once common on lighter caravans. They are simple systems not requiring any electrical connections or a separate brake controller in the car. However, they are only legal up to 2000kg GTM and realistically, they’re effective only on much lighter vans.
Override brakes use the inertia of the moving trailer when the tow vehicle slows down. A sliding mechanism in the trailer coupling moves inward activating a mechanism to apply the brakes. In essence, the trailer tries to ‘catch up’ to the car, and in doing so it forces its own brakes on.
Mechanical versions activate a cable or rod that directly pulls on the brake levers usually paired with drum brakes. Hydraulic versions pressurise a small master cylinder when the trailer pushes forward. This forces brake fluid through hydraulic lines to the trailer brakes for smoother and often stronger braking than a cable system.
By nature, override brakes apply a fixed braking force relative to the movement of the coupling, which can be less precise. Also, there is no way for the driver to independently control the trailer brakes from the vehicle.
Brake controllers
If your caravan has electrically activated brakes, a brake controller in the tow vehicle is an essential piece of the puzzle. The controller is an electronic device that manages the activation signal sent to the trailer’s brakes. Until recently, most brake controllers were aftermarket components retrofitted into the tow vehicle’s wiring harness. Traditional units are typically mounted under the dashboard and more modern units are fitted as a dial on the dash. Alternatively, wireless versions controlled through a phone or separate remote are now on offer. Plus, some cars now have brake controllers factory fitted.
Some vehicles now include factory-fitted brake controllers
There are two main types of brake controllers. Time-delay models are more basic/lower cost and proportional models are more expensive/sophisticated.
A time-delay controller begins applying the trailer’s brakes as soon as you hit the brake pedal (or manual override) but delays full braking force, ramping up over time. You can usually adjust full braking power to come on slower or quicker. Time-delay controllers are simpler and often cheaper. However, because they don’t sense the vehicle’s deceleration, they tend to be less smooth. If you brake gently in traffic, a time-delay controller might still ramp up more braking than needed, resulting in a tug from the caravan. Conversely, in a sudden stop, it might not feed the trailer full power quickly enough.
A proportional (or inertia-sensing) brake controller detects how rapidly your tow vehicle is slowing down and quickly adjusts the trailer braking to match. Inside these controllers, an accelerometer or pendulum device measures deceleration. If you slam on the brakes, a proportional controller will send strong voltage to the trailer brakes. If you’re feathering the brakes down a gentle slope, it will only apply light power. Also, if you are slowing the tow vehicle with engine braking and not the brakes, the proportional controller will activate the caravan brakes where a time-based controller would not. Proportional controllers deliver much smoother, coordinated braking. Ideally, you won’t even notice the trailer doing its share because it is in sync with the tow vehicle.
Some brake controllers are wirelessly controlled through a phone app
Most brake controllers have two user interfaces meaning the unit needs to be mounted within easy reach. The first is to adjust the braking force of the trailer brakes. It is important to follow the instructions and learn how to use the adjustments for various towing conditions. Second is the manual override, a hand-operated control to activate the trailer brakes independently of the tow vehicle to control trailer sway. More on that soon.
Breakaway systems need caravan brakes
In simple terms, a breakaway is a safety device that activates the caravan’s brakes if it ever becomes uncoupled from the tow vehicle while moving. It is legally required on vans with a GTM exceeding 2000kg. The system typically consists of a switch connected to the trailer’s brake circuitry and a small onboard battery. A thin cable lanyard attaches the switch to the towbar or vehicle. If the van disconnects, the lanyard pulls the switch, immediately applying the caravan’s brakes via battery power.
If the pin is pulled out of the breakaway switch the caravan brakes are automatically applied
Breakaway systems require battery power
Sway control systems need caravan brakes
Your caravan brakes can enhance safety well beyond regular stopping. Their superpower is the ability to correct trailer sway. In a trailer sway event, the desired response is to apply the trailer brakes without slamming on the tow vehicle brakes. This action pulls the caravan back into line behind the tow vehicle while also slowing down the van.
Drivers can do this manually via the brake controller’s manual override switch. Experienced towers practice using the brake controller override for early intervention of sway.
However, in a sudden sway event, not every driver reacts in time or has the presence of mind to hit that manual brake switch. This is where automatic caravan-mounted antisway systems come in. Generally known as electronic stability control (ESC), sensors measure the lateral acceleration/yaw of the trailer to detect the onset of a sway.
When sway is detected the caravan’s brakes are automatically applied to counter it. Even the quickest human cannot match the reaction time of an electronic system that senses a sway and activates in milliseconds. Furthermore, some automated systems can apply a measured braking force appropriate to the severity of the sway — gentle for a small oscillation, or harder for a violent fishtail.
ESC systems apply the brakes to manage sway
First-generation ESC systems apply all the caravan’s electric brakes simultaneously at a preset level until the sway stops. The system doesn’t know which side the sway is on, it just slows the whole van down to dampen the oscillation. While these systems are effective, it might not be the most optimal way to realign the caravan.
Next-generation asymmetric systems have raised the bar. Instead of braking all caravan wheels, they can brake each side of the caravan independently. If the caravan swerves left, the system will brake the left-side wheels to tug it back. If it sways right, it brakes the right-side wheels. While asymmetric systems straighten the van faster than symmetric systems, they may not reduce the overall speed as quickly since only half the brakes are used at a time.
Sophisticated systems also modulate the brake force based on sway severity. Small sways get a lighter touch, and strong sways get maximum braking. Often small sways can be corrected before the driver even notices.
It should be noted that most ESC systems are designed to interface with standard electric brake wiring and there are very limited options for hydraulic disc brakes. We are yet to see an asymmetric ESC system for disc brakes. The electric/hydraulic actuator does not have the capacity to brake one side of the caravan independently due to the hydraulic lines being plumbed together.
ABS (anti-lock braking system) and integrated sway control is the latest innovation in caravan braking. Adapted from automotive technology, wheel speed sensors and ABS modulators are added to the caravan’s brakes. If the onboard processor senses the caravan’s wheels start to lock up it will rapidly back off and reapply the brakes repeatedly to prevent a skid. This is a significant safety enhancement because a skidding caravan tyre has much less grip and a tendency to swing out of line, potentially jackknifing. By preventing lockups, the trailer maintains stability and slows down in a shorter distance. Avoiding skidding also helps prevent flat-spotting your caravan tyres under heavy braking.
Electric drum brakes continue to be the standard on Australian caravans
Final thoughts on caravan brakes
Caravan brakes might not be the most glamorous aspect of your rig, but they are arguably among the most important for safety. Braking hardware choices can be divided into popular electric drums, emerging hydraulic discs and rare override systems. Brake controllers are the brains of the braking system sending the message from the tow car to the caravan to activate braking. Even further smarts use the caravan brakes for greater safety. This starts with breakaway systems to stop the van if it becomes inadvertently disconnected from the car and steps up to new technologies like ESC and ABS that can keep your van on track in emergency braking scenarios.
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