There is a huge range of couplings available on the market and your local trailer supplier will carry most of the following couplings. If you require a duo-fit coupling or a have a specific coupling in mind, you may need to shop around. Duo fit couplings have the advantage of fitting both 1 7/8” and 50mm towballs, which are the standard sizes in New Zealand. Other towball sizes are available but you may need to import a coupling to suit the towball. The following couplings are the commonly used and there are many other types available not listed.
Unbraked Couplings
Lever Type
This is the most common type of coupling on an unbraked trailer and is one of the simplest to operate and maintain. There are quite a few different models and styles available and have a multitude of mounting options. Some of the fancier models have a duo-fit tongue arrangement to allow fitting to 2 different diameter towballs.
Pressed Steel Lever Coupling
The pressed steel coupling is one of the cheapest couplings available and is suitable for a towing capacity between 500- 900kg. They operate with a trigger operated lever to close the coupling tongue under the towball and a double action lock trigger/lever trigger to release the coupling. These are only suitable for lightweight trailers and should be regularly cleaned and maintained. This type of coupling can be troublesome if the weather is very cold and wet, especially with cold hands and can jam up if sand or rust gets into the mechanism. They are normally fixed to a straight drawbar with a couple of thru bolts and are easily replaced if required.
Standard Cast Lever Coupling
This coupling is the mainstay of the light trailer industry and is simple by design and function and almost foolproof in its use.
It uses a cast iron enclosure which covers the towball and has a cast tongue which operated by the lever clamps the underside of the towball sphere and is kept in postion by a loaded spring. A locking pin slides over the top of the lever to give additional safety protection by preventing the lever from lifting. The locking pin is turned ninety degrees to locate and lock itself.
Unless poorly lubricated, this coupling will give many years of use and the only maintenance required, apart from the odd squirt of grease is to replace the locking pin and spring as this is the most commonly damaged part of the coupling.
These couplings are rated between 2000 – 2500kg towing capacity and will have their rating cast into the body of the coupling.
Plunger Type Couplings
These couplings utilize a handle rather than a lever to fit and release the coupling and the main head casting is more formed to fit around the towball. The spring loaded tongue comes down at an angle behind the towball and prevents the coupling from lifting. On the side of the coupling a trigger style locking lever is provided to add extra safety. This type of coupling comes with a wear/anti-rattle adjuster on the front of the casting and can be adjusted to take up any slack within the coupling.
These couplings require regular lubrication to ensure continued ease of operation. The most commonly replaced part on this coupling is the the trigger lever, spring and pin and on older couplings the cotter pin between the tongue and handle can wear out and break. If the trailer has too much rearward weight and is lifting the drawbar up,(huge potential for an accident), the coupling can be nearly impossible to remove from the tow vehicle (you may need to get yourself and a couple of your mates to jump up and down on the drawbar to get the coupling to release). These couplings are rated between 2000 – 3500kg towing capacity depending on the braking systems used.
Braking Couplings
Mechanical Braking
Mechanical braking is the cheapest type of braking for a trailer but has its drawback of having one of the lightest braking capacities (around 1200 to 1750kg towing capacity – hub dependent)
The coupling uses a spring dampened movable coupling head which uses the tow vehicles momentum and braking to operate an attached lever. The lever is connected to a pair of mechanical drum braking hubs by cables and depending on the amount of braking the tow vehicle is doing, roughly the same is transferred to the hubs. This type of braking is not overly common, but is used on lower capacity trailers where a little bit of braking is preferred. Constant attention is needed to ensure that the cables have the correct tension to ensure efficient braking.
Hydraulic Braking
Hydraulic override braking couplings are one of the most popular styles of coupling for the 2500kg towing capacity trailers. They use the same style spring dampened moveable coupling head as the mechanical coupling but the rear of the coupling rests against a miniature hydraulic pump system (master cylinder). When the tow vehicle brakes, a proportionate amount of the braking energy is transferred through the coupling to the master cylinder and this pushes hydraulic fluid through tubing to the hubs. The hubs can be either drum or disc style. Maintenance of the coupling involves greasing the main coupling shaft and head and keeping the hydraulic oil topped up. Most master cylinder setups also include a hand brake lever for operating the brakes manually. This brake should only be used for when maneuvering the trailer off the tow vehicle or as a temporary park brake and not used as a fulltime parking brake, especially on a slope. Continued pressure on the brakes can cause leakage around seals or on a poorly fitted joint over time, causing brake failure. Beware of using the brake lever handle as a pivot when moving the trailer, you will bend and break it.
Electric Braking Couplings
Plunger Type couplings as shown are the most common type of coupling used for an electrically braked trailer. Using electric drum hubs and an electric brake controller, these are the most efficient couplings to use. An additional hand brake lever is fitted to the coupling. With cables run back to the drum brakes and adjusted correctly you have a working and reliable handbrake. These couplings are rated up to 3500kg towing capacity.
