DRIVING/TOWING - TOWING
Every year in Australia there are around 160 accidents with the use of vehicle jacks. Deaths and injuries, ranging from amputation and fractures to crush trauma, result from vehicles falling off vehicle jacks.
When you jack up a car or 4WD, only one corner is raised off the ground and the other three wheels have ground contact, limiting how much weight is loaded onto the jack. But when you jack up a trailer only one wheel or pair of wheels has ground contact, along with the coupling on the tow vehicle.
The jack may have to support half the loaded weight of the trailer, not merely a third to a quarter.
The jack stability position is much worse if the ball isn’t connected to a tow vehicle, allowing the trailer to ‘walk’ on its jockey wheel or stand.
Obviously, a trailer or caravan jack needs to be up to the lifting and holding task, but equally as important is where it is positioned.
In the photo a caravan-specific Trail A Mate hydraulic jack is connected to a manufacturer fitted jacking point. This jack also doubles as a drawbar stand and jockey wheel.
There is an Australian consumer product safety standard for vehicle jacks, referencing the Australian/New Zealand Standard AS/NZS 2693:1993 Vehicle Jacks or AS/NZS 2693:2003 Vehicle Jacks (with variations). Clause 4.9 of AS/NZS 2693:2003 defines a caravan jack as:
‘A jack which is limited in its application to caravans and trailers fitted with its specific engagement fitting and is not intended to be used to lift a caravan or trailer at other than the specific engagement points.’
Because weight is distributed differently in each caravan, caravan jacks are required to have an engagement fitting specific to a particular make of caravan. This is designed to reduce the likelihood of accident and injury by providing users with a precise location to position their jacks for the safe lifting of their caravans.
If you have a trailer or caravan and don’t have a specifically approved jack and jacking points for it you should contact the manufacturer for guidance in this vitally important area. The recommended jack types and fitting locations differ widely among makers of similar-looking trailers and caravans.
For example, one caravan with an independent suspension requires a scissor jack under a suspension trailing arm, while another insists on an external post-type jack, fitted to a chassis lifting point behind the rearmost axle. Yet another forbids chassis jacking altogether.
It’s little wonder that many trailer and caravan owners are confused and you have to spend only a short amount of time researching blogs to find a host of widely differing ‘expert’ opinions on how to jack up different types of trailers and caravans.
We’re indebted to the Carvan Council of Australia for the following technical summary of safe jacking procedure.
Caravan jacks must be approved to the Australian Standard; have the top positively located by a mating locating recess to prevent any horizontal slippage; be operational when the caravan is empty and fully-loaded; be positioned on a firm base; have a sufficient load rating and have a sufficient length
A caravan jack must, when on a firm base, be low enough to engage a locating recess when any tyre is fully deflated and have sufficient travel to enable a fully inflated tyre to replace that tyre.
Allowance must be made for the suspension ‘droop’ when the caravan is raised and for the probability that the load on one side of the caravan will be greater than on the other side – typically around 10 percent.
The relationship between a jack’s Load (lifting force) and its Travel, is a basic physics topic of Moments: Force
With the ball as the pivot, the weight over the suspension (M) x its distance (LM) from the pivot must be overcome by the jack’s available Force (J) x its Distance (LJ) from the pivot.
The jack’s available travel (extended length minus retracted length) must be sufficient to enable a tyre to be safely replaced. MxLM=JxLJ
The greater the LJ Distance, the lesser the J Force can be… and vice-versa.
The Caravan Council also urges owners never to trust a jack, because accidents regularly occur when jacks fail or slip.
It is most important to practise changing a wheel before heading off on a trip, so that you know exactly what to do if you have the misfortune to have a punctured tyre on your travels:
Do you know where everything you will need is stored and how to use it all?
Does the wheel brace fit the wheel-nuts and do you have the strength to loosen tightened nuts?
Does the top of the jack correctly suit the caravan maker’s stipulated jacking points? Does the jack have sufficient liftingcapacity (Load Rating)?
Does the jack have sufficient travel and is the minimum height low enough?
Because of the difficulties experienced by many trailer and caravan owners when jacking up their vehicles, there have been several techniques and inventions designed to make the task easier.
Most of these suit dual-axle trailers and caravans, because these are the heaviest and can be more difficult to jack up. For instance, there are many documented reports of people bending axles or chassis, by using incorrect jacking points.
One technique is to run one of the axles up on a block, a rock or a load-levelling wedge, but this often doesn’t raise the second axle clear of the ground.
One invention is a variation on the load-levelling ramp, typified by the Andersen Rapid Jack. This crescent-shaped plastic block is designed to raise the front or rear wheel of a dual-axle pair, by the simple action of the tyre rolling up on it. When that wheel has climbed the ramp it leaves the second one free of the ground, making it easy to change that wheel.
Another variation is the Lock ’n’ Level device that consists of two air bags, joined by a manifold. Both bags can be inflated by a 12V pump, to act as load levellers, or one bag alone can be inflated, to leave the second axle hanging, for an easy wheel change.
Both these devices rely on suspension droop of no more than 130-170mm, or the second axle will still have ground contact.
If there’s too much suspension droop for these devices to work you may be able to fit restraining webbing to the suspension, to limit droop.