Couplings are the most important parts on a trailer as they form the link between the trailer and towing vehicle. This guide should help you purchase fit and maintain them.
These are mainly found on small trailers as by law a trailer used on the road that has no brakes can not gross over 750kg. these are normally pressed steel and fit around a box section and can vary in box size. There are also some better quality cast couplings like Bradley ones these are rated for 2600kg but can only still be used to pull 750 kg on the road.
These are easy to fit and setup normally there are 2 vertical bolts to go through a box section all that is required is to drill 2 holes through the drawbar and fit the bolts throught the coupling and the box section. we recomend that these bolts are high tensile and have a washer on each side with a nylock nut to prevent them from coming loose. The Bradley couplings are designed to be bolted to a pleat but it is a simular fitting procediour. There is no specific height to to set a coupling but we strongly recomend that if you are building a trailer from scratch that yo try and make the coupling suit a towball with a height to the center of the ball of around 400mm from the ground when un loaded when the trailer is sat level. the reason we recomend this is that towballs on passanger vehicles that comply with EC94/20 should have a height of 350-420mm when fully loaded, if you know this will be towed by one particular vehicle it is always a good idea to match the trailer to the towing vehicle. when doung this with a twin axle trailer it is always an idea to set the coupling slightly lower than the towball to give a little nose weight and to stop the trailer lifting the rear of the car as this can make the car jack knife when the trailer wants to go in a straight line and pushes the rear of the towing vehicle that has little traction. Also if the coupling is lifting the vehicle it can cause excessive wear on the coupling and towball and eventially the coupling could fail and you could loose the trailer.
Secondary coupling cables.
By law you must have a secondary coupling cable fitted to an unbraked trailer in the case of the coupling failing this is a heavy duty cable or chain that attached the towing vehicle to a trailer / caravan. This should keep the trailer from straying if the coupling fails. we recomend that this fitted indipendantly, this means avoid fitting to coupling bolts and the towball where ever possible. if you fit around the neck of a towball and the bolts on towball fail or come lose then there is no effect taken by the cable as it has come off with the towball and it is the same if fasterned to coupling bolts. This is very difficult as secondary coupling cables are short to try and stop the coupling hitting the floor.
With an unbraked coupling there are not many things to maintain. Basically a coupling must be kept greased and clean also the mechanisium must be oiled, also you should inspect the coupling to make sure there is no wear where it attaches to the towball and make sure it is securly attached to the trailer and the bolts are not loose.
A coupling must be kept clean as debris in the coupling can stop the coupling attaching to the towball properly and it can cause excessive wear to the coupling and towball.
The coupling must be greased inside to allow the coupling to pivot easily and not wear the inside or the towball.
The mechanisum from the handle to the ball must be kept oiled with thin oil to keep it working correctly.
The coupling must be regually checked for wear or damage to avoid the coupling from failing.
To be finished shortly.