DIY caravan shock absorbers

It's shocking, but the dampeners in your vehicle’s suspension might be your van's most neglected and underappreciated components. These lonely shock absorbers under the floor play an essential part in keeping the tyres on the road, minimising vibration, controlling sway, and managing spring movement over rough ground.

A common misconception is that shock absorbers help support the weight of the van. They don’t.

Our travels over 2022 taught me a great about this important part of van maintenance because it took three differing professional opinions and many miles on our journey to WA to track down unusual tyre wear, especially on the left rear of our 2012 Trakmaster, which we acquired about a year ago.

My initial reaction was that the wheels were out of alignment, but a mechanic in the middle of nowhere was sure it was the low quality of the aggressive all-terrain tyres. I travelled on to Esperance, where the advice was that it was the alignment but that they couldn't look at the van for a month. In Albany, the repair centre told me the wear wasn't because of alignment. They checked it anyway – it was within tolerances- and convinced me it was a problem with the shock absorbers. None were available so we carried on and eventually returned home with the problem unsolved.

A shock absorber is a hydraulic piston between the caravan chassis and the wheel. As the wheel moves over bumps in the road, the piston travels up and down and forces oil through small valves to slow the movement of the piston. The size and design of the hole determine the dampening rate, moderating the spring movement and converting the kinetic energy to heat.

Over time the heat and vibration will reduce the shock absorber's efficiency, and in extreme circumstances, it will lose oil and the dampening effect. When this happens, the wheels will continue to bounce, causing uneven tyre wear and potential damage to suspension components.

One sign that the shocks are past their use-by date will be evidence of heavy oil leaks, but some misting isn't uncommon. Our existing shocks didn't show damage, but once off the van, they were much easier to move in and out than the new ones.

Our model Trakmaster uses the independent Sugarglider suspension and Pedders shocks. You could choose an aftermarket brand with the same open and closed length and strength. Most old shocks will have a part number stamped on the metal body for easy identification to help chase new parts.

While the Trakmaster owner's group had some alternative suggestions for other shocks, I decided to go with the standard model on the advice of Jason at Halen Vans, who specialises in all things Trakmaster. He supplied four shocks at around $250 each.

Replacing the shocks

Replacing your shock absorbers should be straightforward with a set of basic tools. As in all things mechanical, make sure the working area is safe. It may be possible to jack up the van and remove wheels to access the shock absorber, so the van must be well supported under the chassis. Rather than remove the wheels, you can choose to work underneath the chassis with the tyres safely secured on blocks for a bit more room and this is the path I chose.

As the task is to remove and replace the old shocks with four new ones, it's a good idea to note how the old components come off. So, start with a small tarp under the work area and a parts tray to collect all the nuts, washers and bits and pieces. Next, take a photo of where the fittings came from or store them in plastic bags to separate the top components from the bottom ones.

Each shock will have a top and bottom bolt through the eyes, and it's an excellent trick to undo the bottom bolts first to stop the shock from swinging down and hitting you. If the old shocks were fitted using a rattle gun (a no-no in good mechanical practice) then a long spanner would be helpful to get the nuts loose. The bolts should come free quickly, but if the rubber bushes have been pinched due to overtightening, a rubber hammer will move them.

The new Pedders dampeners didn’t come with new crush tubes, which separate the rubber bush and the bolt, so I removed the old ones. They were easily hammered out with a small spare 10mm socket I had, but anything of a similar size will do the trick.

Reassembly

Reassembly is the reverse of removal. Starting with the top bolt, the shock absorbers can be moved into place by hand. Use a new Nyloc nut, and in the case of an offroad van, it's a good idea to cover any exposed thread with a second nut or a nylon sleeve to prevent stone damage.

Getting the proper torque setting for the nuts from manufacturers is almost impossible. I tried several Pedders outlets and their head office but have yet to succeed. The best advice for correct tightness came from our friends at Couple Mate in Queensland. They advise that overtightening will excessively squash the rubber bush and reduce its flexibility, causing premature wear and possibly breaking the eye or bolt. Under tightening can lead to the nut coming loose and potentially stripping the nut off the tread, allowing the shock absorber to move and eventually slide off the mount.

Couple Mate advises that shock absorbers should be tightened with a spanner rather than a rattle gun to avoid over-tightening.

When tightening up the shock absorbers, rotate the nut until you feel it contact the outer mounting washer and bush. Two full turns of the spanner clockwise should secure the shock absorber in place. Grab the shock and ensure it does not rattle on the mount and that there is still flexibility in the bush. The shock absorber is too tight if the bush is bulging over the outside of the washer. Watch out that the rubber boot is properly positioned as it can move off its mounting slot as you manipulate the shock into place. Without a tight fit, dust and mud can settle on the stainless-steel shaft and cause damage. You might notice in the photos that I freshened up the paint on the suspension to match the shiny new shocks.

Remember to check the mounts after you have towed the van for a hundred kilometres and again during regular service or if travelling over rugged terrain for extended periods.

With the new shocks in place and new tyres all round we headed to North Queensland and back with the van behind. After around 5000km, the tyres show minimal sign of wear. The most noticeable difference in towing has been that the van no longer moves when a big, enclosed semi comes past. This makes sense as the resistance of the shock absorber slows the driver side edge from compressing and the opposite side from expanding. I think the change has been a success.