HOW MUCH DO YOU KNOW REALLY KNOW ABOUT YOUR CARAVAN’S AXLES?

Your caravan’s axle(s) are one of its most important components. But when is the last time you actually thought about it, let alone inspected it? The entire weight of the van rests on the axle, minus the ball weight. So whether your van has stub or beam axles, let’s look at the ins and outs of the crucial piece of equipment.

AVOIDING AXLE FAILURES

Axle failures can and do occur, though arguable an axle system that is truly fit for purpose and has been properly maintained should not fail.

What would constitute improper use of an axle? For a start, much depends on how you load your van. Consistently overloading a caravan – i.e., exceeding the weight capacity of the axle – is asking for trouble.

Axle failures can occur if the travel of the suspension is compromised, so the shock load is transferred into the suspension instead of the suspension medium – i.e., the spring or airbag. Failures can also occur if the suspension is used in a way it was not designed for. An example might be driving too fast for the conditions, leading to a situation where the shock loading exceeds the shock load the suspension was designed to cope with.

Owners of tandem vans have a particular responsibility when it comes to minimising stress on their rig’s running gear. Tightly ‘jack-knifing’ or ‘screwing’ the van in order to turn around, for example, can cause the tyres to distort on the rims and place massive lateral forces on the van’s running gear. These forces can exceed the lateral forces that occur under normal towing conditions.

BUYING USED

If you’ve ever inspected a second-hand caravan, there’s a good chance that you didn’t think to inspect the axle(s). The truth is, it can be difficult to identify any potential faults or defects here. However, it is often easy to spot a repair.

Caravan repairers can be a useful source of information. Why not ask them about the specific issues affecting various axle types? And remember: if you find a repair on one side of the van, always check the other side too.

It’s worth pointing out that a repair doesn’t always indicate a failure – it may be a repair to damage caused in a small accident, for example.

Fatigue in stub axles, found in independent suspension systems, is hard to spot. You can, however, identify a bent stub axle by initially checking the gap between the backing plate and the back edge of the brake drum. This should be parallel. If it’s not, there’s a problem.

GROSS TRAILER MASS

A trailer’s group axle rating should be equal to – but preferably greater than – the trailer’s Gross Trailer Mass. If it isn’t, it’s time to walk away from any potential purchase. Or if you already own a van, seek recourse if possible. If not, it will be necessary to see a caravan specialist to have the situation properly rectified. In any event, the running gear of a caravan is only as strong as its weakest link. The GTM should never be lower than the lowest-rated ‘link in the chain’.

Fortunately, the above scenario is uncommon. Additionally, reputable axle/suspension manufacturers will stamp their products with a weight rating as well as a serial number.

If you’ve just purchased a new or second-hand van, it’s a good idea to load it as you would for a trip, including with full water and gas tanks, and visit a weigh-bridge. With the van still connected to the tow vehicle, position the van so that only its wheels are on the weigh-bridge.

The weight on the weigh-bridge ticket must not exceed the van’s Gross Trailer Mass on the van’s compliance plate or the weight capacity stamped on the axle.

SUMMING UP

Like with anything, you get out what you put in. If your van has been fitted with quality, reputable axle(s) and suspension, and it is treated properly over the course of its lifetime, it is unlikely to mysteriously fail.

If you take anything away from this article, let it be this: be aware of the ratings of the axle set/suspension system. These are there for very good reason. Never exceed them!