Technical Topics No. 11

HOOKING UP.
Before you hook your vehicle up to your trailer there are a number of things to consider. Some of the following information will only apply to the first time you hook up to your trailer and will not need checking while the same trailer and vehicle is used.

TOW-BALL WEIGHT.
The first thing that needs to be checked is the height of the tow-ball on your vehicle in relation to the trailer's coupling. This has to be carried out on level ground. The vehicle and trailer should be laden to about the same weight as they would be used. With the trailer sitting level (see fig 1.) and the vehicle backed-up to within about 100mm of the trailer coupling the height of the centre of the towball and the trailer coupling should be about the same (see fig.2). If there is any great difference it may be necessary to re-distribute the load in the trailer or purchase a different height ball-mount etc.

TOW-BALL MASS
Tow-ball mass is an important requirement for safe, stable operation of your trailer and vehicle combination.

Next, the tow-ball mass of the laden trailer needs to be considered. This can be measured with some basic household materials. You will need three (3) pieces of 100 x 50mm timber, two (2) pieces about 300mm long and one (1) piece about 1m long. You will also need one (1) short piece of broom handle or water pipe about 25-30mm diameter and one (1) piece approx. 200mm long square section timber or steel 25 or 50 mm square and one set of bathroon scales.

Position the trailer on a flat, level surface. Make sure that it is sitting level as in fig. 1.
Standing at the drawbar and looking at the trailer, place one (1) of the short pieces of 100 x 50mm timber on the ground a300mm to the right of the centre of the trailer coupling.
Next, place the bathroom scales to the left of the trailer coupling so that its centre is 600mm from the centre of the coupling.
Now place the 25mm square piece of timber or steel on the top of the 100 x 50mm piece of timber on the ground and the piece of water-pipe or broom handle on the centre of the scales.
The long piece of timber is now positioned across, and resting on both the piece of round material and the piece of 25mm square timber or steel.
Position the other piece of short timber vertically under the trailer coupling and on top of the long piece of timber and lower the trailer jockey wheel untill all the weight of the trailer is taken by the vertical piece of timber and the jockey wheel is just clear of the ground (see fig. 3).
The tow-ball mass can now be determined by multiplying the reading on the scales by three (3).

Ideally the tow-ball mass should be within 5 to 15% of the laden mass of your trailer.

Compare the measured tow-ball mass with the recommended tow-ball mass as specified by the trailer manufacturer.

If there is any great difference between the meaasured and recommended tow-ball mass it may be necessary to re-distribute some of the load in your trailer. Moving items towards the rear of the trailer will lighten the tow-ball mass while moving items forward will increase the tow-ball mass.

TOW-BALL AND COUPLING.
Check the security of the ball mount or tongue securing bolts or pin and check the tightness of the towball securing nut.
Lubricate the towball and coupling with a light smear of molybdenum based or high-pressure type grease.
Line-up the towball under the coupling body and lower the trailer coupling onto the ball. Ensure that the coupling lock is sceured when it is lowered into position.
Connect the safety chains ensuring that there is ample length to allow turning of the vehicle and trailer. Two chains should be used and they should be fitted so that they cross-over under the coupling/towball.
Check the operation of over-ride brakes.

LIGHTS.
Plug in the electrical connection and check the correct operation of all lights.
Make sure that the electrical cabling does not interfere with any of the coupling equipment
Check the condition of all lights, lenses for cracks or fading and security to the trailer body.

BRAKES.
Where over-ride brakes are fitted to the trailer ensure that the reversing lock, if fitted, is released.
Check that the coupling if free to slide back and forth on over-ride brakes (if fitted).
With a vacuum operated braking system, connect the vacuum line and check brake operation with the enging of the towing vehicle runing.. Also check for any leaks around the connections and hoses.
With electric brakes, check adjustment of the hand control, as per the manufacturer's instructions. Operate the foot and hand controls seperately, with the ignition turned on where necessary, and listen for activation noise at the trailer wheels.

BODY.
Fully raise all under body stands on the trailer.
Fully raise the jockey wheel and secure or remove as necessary.
Remove any 240 volt leads (if connected).
Remove drainage hose or bucket.

STABILITY.
Fit any weight distribution bars or sway controls if necessary, as per manufacturer's instructions.
Check tyre pressure, including the spare wheel.

SECURITY AND SAFETY.
Secure any loose items in the trailer and ensure that any cupboard locks are latched properly.
Close or lower all hatches, windows and awnings and make secure.
Turn off any LPG cyclinders and switch any fridge to 12 volt operation. Fit extension mirrors to the towing vehicle where necessary and adjust all mirrors so that both left and right corners of the trailer are visible from the driving position.
Lift any trailer steps and securely latch doors and tailgates.

The information in the above article was derived from an NRMA publication - "Towing in Australia", dated March 2001.