air suspension

"Spend a bit more money on appropriate replacement springs."

That may not solve the problem here Phil. Heavier springs will support weight directly above them. The axle may be overloaded but the springs can't help that.

If the excess load is back past the axle, the springs are useless. If you push the rear end of the car down hard enough and far enough it will pivot on the axle and lift the front wheels off the ground. If you tried that the chassis would most likely bend while you watched it..

You could install the heaviest spring or air bags on the market and then push the back way down and the car will still pivot on the chassis and lift the front.

That is why chassis break and will continue to break as long as owners think new springs will fix their sagging rear suspension. It is the heavy material sitting well back on the end of a lever i.e the distance between the axle and the end of the car or tow ball that does the damage when the car is travelling on any road surface that causes it to rise and fall rapidly

The end of the chassis is constantly lifting the material up quickly or catching it when it falls resulting in it flexing up and down outside its design limits.
.
The only thing that will give any support to the far end of the car is a weight distributing hitch but you must be towing something to use one and they can damage the car, the tow bar or themselves if the angle between the car and trailer gets too high. This rules them out on rough bush tracks.

If anyone disagrees then please tell me how you support the far end of the chassis without putting a coil spring between the chassis and the road.

Splits there are 2 main reasons why upgraded springs are better than adding coils.
Coils place the weight on a section of chassis that is not built to take it where as upgraded springs put that pressure on the spring mounts. (Where it should be)
Quality upgraded leaf springs have a larger number of thinner leaves with a greater camber which are not as harsh as stock springs nor do they bottom out as often so transfer less shock through to the chassis.
That said it's the overall weight & where it's positioned that causes problems. Suspension upgrades should not be seen as a fix for overloading rather to improve the ride, ground clearance & wheel travel.

"Quality upgraded leaf springs have a larger number of thinner leaves with a greater camber which are not as harsh as stock springs nor do they bottom out as often so transfer less shock through to the chassis."

The only problem there is the stock springs are designed to be flat or very close to it when fully and correctly loaded. That is to induce a certain amount of roll understeer into the suspension which assists in stability in corners.


"That said it's the overall weight & where it's positioned that causes problems. "

True but far too often aftermarket springs are seen as the correct way to lift a sagging rear end that has too much weight too far back behind the axle. All the springs do is compress and tilt with the chassis as the rear goes down hard and the front of the chassis is jerked up.

"Splits there are 2 main reasons why upgraded springs are better than adding coils."

I was not suggesting putting coils into the suspension. I said between the far end of the car and the road. That is not possible but it is the only way, apart from a WDH, to support the end of the car as it falls down behind the axle.

In order for owners to understand this whole thing a lot better you have to think of the difference between weight and mass. Weight is just a measure of the pull of gravity. We see it as number showing on some scales. It does not change. Mass is the amount of material in something.

If you place a 120 kg block of concrete onto 120 kg bathroom scales you will get a reading of 120 kg. That is weight. If you pick the block up about 300 mm and drop it onto the scales, it will most likely smash them beyond repair. Its weight is still 120 kg but the material in it built up momentum when it fell and hit the scales very hard as they bought it to a sudden stop.

That is what happened to all the cars that have bent their chassis, axle housings or whatever. They were ok while in the garage at home but the situation changed dramatically when they were put into motion.

If you load a car incorrectly and have to resort to aftermarket parts to solve the problem, there will always be a question mark hanging over its reliability. Many get away with it but many don't.

That's why you need to figure out what set up suits you best a spring upgrade or air bag assist and don't over load them. They are designed to assist or share the load and not take the full or most of the load by themselves that's where people mostly go wrong and then the easy way out is to blame the air bags heaven forbid should the driver be responsible or get blamed for creating their own problem due to lack of applying simple common sense
.
So to be truthful it's a bit of a story. I have the correct springs and shocks that suit my twin cab GQ I fitted them about 3 yrs ago Tough Dog adjustables, TJM 2" extra heavy duty springs up front and 2" heavy duty at the rear they have worked fine and are still fine. I also put the old poly airs back in the previous owner had fitted I used them for carting the occasional heavy load of rocks etc but about 2 yrs after the suspension upgrade 1 poly air split they were 9 yrs old so I took them out.
Since then I permanently fitted a canopy, batteries, 60ltr water tank etc etc and because I planned ahead what I was going to do with the vehicle which is set it up for touring I had already fitted the springs to suit my future mods they supported the extra gear fine. So then I got an idea that I would like to try air bellows in the rear after helping my neighbour fit some to the rear of his BT50 happy with them they work well nothing wrong with trying something that's been used in cars, 4WD's, trucks etc successfully for yrs. Still have the coils in the shed If I want to change them back. While these are not the best pics to go off my vehicle is still sitting slightly higher in the rear with extras fitted. Also the rear axel is closer to the centre of the tray than most twin cabs and the spare wheel which weighs 35 kg, I'll be running 2 soon it's not hanging off the rear creating another problem like lots of people have done without thinking first about load placement I would never hang spares off the rear of any factory build twin cab on the market and expect it to be ok.

That is a very sensible set-up Batts!!!

Lengthen the chassis AND having the tyres up behind the cab!!! 10 out of 10.

Very similar proportions to my Chevy. I have air bellows (100psi rated) in the Chevy, but only because they were on it when I bought it. I don't run more than about 5 psi in them.

Roachie

Thanks Roachie the batteries, water tank are in front of the axel as well try to only put lighter stuff behind it and the canopy being alloy only weighs 120 kg empty. My bellows are 150 psi rated and tested to something like 750 psi I run around 80 psi.

If you have factory springs you can change them to a better quality spring like O.M.E. their usually sold through ARB and getting shocks to match will also make a difference. You just need to talk to them and explain what you're after.


You can also find out about parabolic springs they have been around for a while so they have had time to get them right. If you do a search you may find a company near you that deals with them. http://www.westraliasprings.com.au/category/4wd_parabolic_suspension/23