Why Ute Chassis Break

Ron Moon — 10 August 2015

Do some research on the internet and you’ll see heaps of examples and a plethora of excuses as to why ute chassis break. But the major reasons cited are overloading the vehicle and the use of airbags to help carry the load.

Over the years, we’ve had a fair amount of experience with cracked chassis; it’s not a new problem. What is new, however, is the number of dual cab utes running around and tackling desert tracks, the number of people towing trailers, and the now-widespread use of airbags as an aid to vehicle suspension when carrying heavy loads.

Back in 2001, we ran a trip across the desert along a number of the Beadell roads. One of the participants had an extremely overloaded dual cab, mainly with the amount of fuel he was carrying (he didn’t have a trailer or airbags to aid suspension). When we suggested it wasn’t required as we were passing fuel outlets, he replied that he wasn’t going to pay those “rip-off bastards” when he had enough fuel to do the trip. He ended up paying in other ways! We welded up his chassis west of Well 33 on Wapet Road, and again when we had better gear at Eighty Mile Beach.

So, what are our recommendations after speaking with the experts?

First up, know what your vehicle weighs — especially when it’s fully loaded. Most people will be shocked when they run their rig over a weighbridge. Remember, the GVM of a vehicle includes everything you’ve packed, the accessories fitted, the fuel — and the occupants.

Set up your vehicle’s suspension properly by talking to a suspension expert and if necessary, fitting good-quality aftermarket suspension. If you’re going to use airbags, make sure you fit appropriate ones. For example, Polyair have three different-sized bellows to suit leaf sprung vehicles; be careful not to run them over-inflated.

Keep an eye on the car’s weight when packing for a trip and load heavy items including jerry cans, tools or water as far forward as possible. Keeping weight to a minimum — in both your vehicle and trailer — is always a good thing.

If towing a trailer, note the overall weight of the trailer, the ball weight and how you load it.

Finally, slow down when you’re on a dirt road or track. Hitting any whoopty-doo, creek, gully or gutter at speed is bound to cause issues. The damage might not be noticeable straight away, but it certainly will be further down the track.

10 common chassis-busting mistakes and how to avoid them

1. Spare wheels carried on the rear of the vehicle place enormous strain on the chassis when traversing bumps and undulations. To reduce this, try to carry extra spares within the wheelbase — either on the roof (if the vehicle’s roof rating allows it) or against the tray’s headboard.

2. Heavy camping gear including water tanks and fridges should be installed or carried as far forward in a single or dual cab ute as possible. Same goes for heavy things such as chainsaws and recovery equipment — within the wheelbase is the best place for the weight.

3. A fridge on a steel slide can weigh 60kg, and some slide-out drawers can weigh in excess of 70kg, even when they’re empty! Keep the weight of accessories and permanently installed equipment in mind when planning and buying equipment for your rig.

4. Add-on airbags in a vehicle’s leaf-sprung rear suspension place a point-load into the chassis that, if the worst happens, can cause bending. Upgrading the leaf-spring suspension is preferable as the chassis continues to carry weight where the vehicle manufacturer intended.

5. If you’re installing a box or service-style body, be sure it has structural mounts over the axle centre line, not just at the four corners. This spreads the weight more evenly into the chassis rails along its length, reducing the risk of a fracture above the axle line.

6. They may appear well-balanced and with moderate ball weights (under 100kg), however, many trailers carry heavy spare tyres and other equipment a long way from the axle centre. In undulating offroad conditions such as sand, the inertia effect of this weight during vehicle pitching can bend the chassis.

7. Weight distribution hitches are not suitable for use offroad as they place considerable stress on the chassis when “jacking-up” the rear of the vehicle. This stress increases immensely over terrain such as drains and creek beds. Need a WDH? Stay on the blacktop.

8. A GVM upgrade may allow a vehicle to legally carry more weight, however, it does not increase the strength or durability of the vehicle chassis. Your GVM-upgraded vehicle is likely to cop some damage if it is carrying more weight.

9. Take your vehicle to a public weighbridge and weigh it with all your equipment and full tanks to discover your real front and rear axle weights: you may be shocked. Racers know that “lightness is performance” and it makes just as much sense offroad.

10. No matter what your mission, keep your speeds sensible. Bush and outback roads can throw out many perils such as cattle grids, pot holes, creek beds and cross-track gutters after storms that can all bend and break a heavily-loaded vehicle’s suspension or chassis.

Check out the full feature in issue #91 August 2015 of Camper Trailer Australia magazine. 


chassis repairs ute mechanic fix