Monday, Aug 04, 2014 at 12:55
"But that was from installing airbags between the spring hangers."
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Air bags make chassis bending a little easier but they are not the only cause of chassis damage. They are exponential springs as opposed to your leaf springs which are linear. They get progressively harder as they compress, just like bump rubbers do. The air pressures required to make them lift overloaded rear ends will result in them hardening rapidly by the time they are around 40% compressed and they will be like a
rock at 60%. They usually bring the chassis to a sudden stop before the leaf springs would have allowed it to get down to the original bump rubbers. The result is the chassis usually bends at the top of the bags. Without them it is usually closer to the front spring hangers.
Keep in mind heavier springs do not alter the leverage effect on the back of the chassis. Only a WDH will do that and I think that is not readily understood by many owners.
Imagine a car for example with no trailer but with the two hitch bars in position on the tow bar. If you were to lift the ends of them with a crane, and assuming nothing broke, you would eventually lift the rear wheels of the car off the ground. You would have lifted all the weight off the axle and transferred a lot of it to the front wheels.
You can not do that with heavier springs or air bags. The wheels are still on the ground, the weight is still on the rear end of the chassis and nothing has been transferred anywhere. All you have is an incorrectly loaded rear end sitting up a few inches higher. The chassis is still at risk as plenty of owners have found out.
Your big problem could be the high tow ball weight on your 3 ton van. I noticed on the Track Master site that they list the required towing capacity of cars for each model. The car manufacturers list a maximum towing capacity only. It usually for good condition like highway driving only and should be reduced as conditions get rougher. The first thing I would do is ring Ford on their customer information number and discuss it with them. They made the car so ask them, not the van manufacturer or dealer.
They may rule out a big van with the physical dimensions and weight distribution of yours. I noticed Mitsubishi has been criticised on the net for claiming the Pajero will tow 3000kg but if you exceed 2500 kg, the tow ball weight must be reduced considerably to a point that eliminates many big vans. What they are saying is yes it will tow and be able to control some 3000 kg trailers or whatever in certain conditions but they are not heavy enough or long enough to control a 3000 kg van at highway or freeway speeds. Your
Ranger will tow your van ok but the van will stretch it to the limit when it comes to controlling it if the van is ever subjected to a sudden change in direction at speed by wind or whatever.
If Ford are anything like the manufacturer of my ute, they will tell you a WDH must be used if the tow ball weight exceeds a certain number of kgs. This means some of that high ball weight must be taken off the back and moved to the front. The trouble here is WDHs on off road vans don't always work very
well. If you get too great an angle between the car and the van in rough conditions, the tow bar, car or hitch can very easily be damaged. The hitches are usually used in flat conditions only.
Take note of what Whirlwinder said about the seats. That could have been a major factor in bending the Triton chassis in the photo. The
Ranger has three load bearing areas: the five seats, the fuel tank and the back of the chassis. All must take their full share of the load if you take the car up to GVM. You can't have a couple of average weight people in the front and the rest out the back.
The weight of your tray, the tow bar, the ball weight, the people in the seats and any other accessories must also be deducted from the carrying capacity
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"You would think that if they rate 1 ton payload with 350 km down force on tow ball the vehicle should withstand any breakages".
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That is static weight only. It is a very different story when it is in motion. You could place a brick on your bare foot without any problems but drop it onto your foot from about 300 mm and you will instantly notice there is a big difference.
When the 350 kg on your tow ball falls suddenly as your rear wheels drop into a small washout or whatever in the road, the forces generated will increase by the square of the distance it is behind the axle. The ball will be around 1.2 metres back making the force on the end of your chassis around 504 kgs. Whatever else is behind the axle will also add to that force.
This is why so many people have chassis problems. They look at static weights only but don't stop to think what happens to all of that material when it is in motion.
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