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Defining Vibration Fatigue | Caravans and Boat Trailers

by | May 15, 2016 | Trailer & Caravan Safety | 0 comments

Vibration Fatigue in Caravans and Boat Trailers

Vibration fatigue in caravans and boat trailers is one of the leading causes of bearing failure, spring failure and failures associated with your running gear.

Have you ever seen an axle wobble in the middle as its owner drives down the highway, oblivious to what is occurring under his rig?

In America, the hollow axle is the most popular axle by far. This video demonstrates the effect of vibration on electric wiring run through a hollow axle.

This causes axle flex suspension fatigue. Poorly manufactured axles are another cause.

The driver probably feels a slight vibration or something stranger than the last time he towed but cannot quite put his finger on it.

Have you seen the Air Crash investigation and heard them mention vibration fatigue?

Vibration can also occur when axles are too long. For example, 39mm Round Axle @ 2000mm on Max weight of 750kg

The axle beings to vibrate, and the vibrations go throughout the trailer and cause numerous problems.

The common problems of vibration fatigue are premature spring aging, spring collapse, shackle bolt, Bush and spring shackle plate wear, constant bearing failure and bearing destruction. Then there are huge problems inside the rig.

Now I am only mentioning boat trailers because the addition of rust accelerates vibration fatigue; however, vibration fatigue applies to caravans and campers more so because these Grey Nomads have a lot of equipment inside their trailer.
vibration fatigue

Here are the tell-tale signs of vibration fatigue.

  • 39mm Round or 40mm Square Axle is overweight.
  • Too wide for a 39mm Round Axle would be 1800mm @750kg
  • and 2000mm @ 1,000kg for a 40mm Square.
  • Loose u-bolts are caused by vibration fatigue.

If you have doubts, put a straight edge on your axle beam. If the gap is more than 5mm, you will get vibration fatigue. The more significant the gap, the bigger the problem.

Get your mate to follow you down the highway and do a small test.

Accelerate to 100 km and have a good look at your axle. Lower the speed and reduce the vibration fatigue.

How do I fix vibration fatigue?

First, you need to identify fatigue as follows:-

  • Bearing Failures and
  • Spring Failures

Why Caravan Bearings and Boat Bearing fail

The following measures can cure fatigue:-

  • Axle upgrade
  • Spring Upgrade
  • Shock Absorbers
  • Top Tip: Let the air out of your tyres, say 25 psi, on corrugated roads, then back to normal pressure on the highway.

Once your rig is vibration-free, then Shock Absorbers are a necessity.

If you have doubts, call us, but it is wise to go and get a weight bridge certificate. Manufacturers’ weights are always under-done.

Add 200kg for fuel and bait, and you are close to your accurate on-road weight.

If you are thinking about Independent Suspension for your rig, this type of suspension has zero axle flex.

Here is some research data completed some time ago on, in 1979.


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