WDH vs Air Lift Shocks

Two entirely different animals. One will not take the place of the other. WDH (ie) Weight Distribution Hitch. Levels the vehicle and puts weight back on the Steer, Air shocks simply just let you overload the back of the vehicle.

Have a read of these mate, and particularly have a think about where the load point goes when you fit air shocks to do the job of inadequate springs for the task.

wonder why


thread

Three different animals involved here possibly.

1. Air shock absorbers. These will give a mild lift to the rear suspension but take note of where they are putting that lift. The attaching points were never intended to support a considerable amount of the weight of the vehicle. Just a mounting point to let the shockies do their job of dampening the spring rebound.

2. Rear air bags. These will take a lot more weight as they put the loading points on the axle and vehicle chassis. As has been mentioned with coil springs they usually go inside the coils so putting the extra lift in the same points as the original springs. With leaf springs they put the extra lift between the spring to chassis attaching points. Not where it was designed to go. A mild amount of air pressure may, repeat, may, be ok depending on the chassis and the amount of air pressure. IMHO not the best option.

3. The WDH (weight distribution hitch) Once again as has been pointed out, a completely different animal intended for a different job, i.e. restoring weight to the front axle lost by the lever action of the tow ball weight. Be careful of trying to restore all lost height as this is in my opinion only a rough guide but all that is available to the average bear. Putting too much tension on the spring bars puts extra loading on the vehicle chassis and van draw bar. Also loss of too much weight on the rear tyres can compromise their grip on the road and hence their ability to control any sway.

Now all of the above is my opinion based on observation, information gathered from others when doing my own research and a dash of common sense. I make no recommendations one way or the other.

Cheers
Pop

There are two things that keep popping their heads up in the market from time to time and in slightly different forms.

Helper springs of some sort and load boosting shockies of some sort, both are cheap short cuts that do not solve the problem and can most definitely cause other problems.

Back in the late 70's and early 80's air shockies where big business.....just about every auto sales catalogue had some sort of offer on air shockies...lots of people used em for towing or jacking up the rear of their vehicle for one reason or the other.

They had a number of problems...the obviouis one was the placing of load where it was not designed to be borne, on the shockie mounts.

They where also commonly carrying way more of the load than they realy shold have been or pumped up further than they should have been unloaded.

this gave rise to a couple of problems.

because the air circuits where mostly common between the shockies...they provided extra spring rate but not extra roll resistance...going round a long corner one shockie would pump up the other, resulting in stability problems leading to rollovers.

Some ran seperate air circuits for each side...this gave rise to another problem.....rollovers from shockie failure.....one over loaded or over inflated shockie would suddenly fail resulting in a substantial spring rate reduction on one side and agan a rollover.

These things where prone to failure..particulrly as mentioned when over loaded or over inflated..

Air bags as currently in the market have the potential for the same problems...they seem to be less prone to failure, but there are many documented cases of chassis induced failure from after market airbags....to the point where some vehicle manufacturers specifically exclude rear chassis failure from their warranties where airbags are used.


Helper springs where very popular in the late 70's and early 80's, you could buy em at most auto accessory stores.

They placed the load on the suspension mounts where it was suposed to be, buy thete where most definitely a cheap alternative to replacement springs.

There where then a few helper springs that did not place the additional spring support on the ends of the springs where it could be best supported...some may have been short additional leaves some may have been half leaves.

Though many people used them and raved about them, none of these where realy good options.

Back in the day, helper springs where a poor substitute for having the spring pack reset and an extra leaf or two fitted.


come the new century and what should I see...the helper spring making a come back...touted as wonderfull and marvelous backed be a couple of major brand names.


None of these solutions to overloading, inadequate suspenion or poor set up of the trailer.
cheers

Tony,

I think you need to revisit the advise and the product you are talking about.

You say that you want to do a bit of "off road" travel. My comments are based on off road, not on road.

A WDH will be fine for dirt road driving bit will restrict the vehicle/van flex off road, so you would need to remove the WDH for these occasions and you would be back to square one.

Air Shocks are designed to lift the vehicle taking over from the springs, I do not know any vehicle that has shock mounts designed to take the vehicles full weight off road. Both Monroe and Gabriel state temporary or occasional towing.

The issue with air shocks is that a shock has a defined length to work, putting in an air chamber then inflating it shortens the stroke of the shock reducing vehicle suspension travel, a shortened length with the same amount of oil I would suggest would change the dynamics of the shock and the ride would be solid. This is a no no for off road.

The down force on the rear of you vehicle when towing off road in some situations will can be more that the rear axel load.
While Suspension upgrades and air bags may be expensive, the suppliers/installers normally have a fair idea of what the end result will be.

This diagram clearly shows the effects of loading on the front wheels both with and without WDH


If you have the tub of your ute fairly well loaded then the upward lift of the WDH will be somewhat balanced by the downward loading from the load in the tub.

With all the previous on the forum about bent chassis I think you have to be a Richard Cranium if you fit them. Read all the links on on this page and I don't think you will consider them again.

This all comes back to the whole "off road" thing.

Towing something on "smooth improved pavements" is one thing, towing something off road is a whole other thing.

Towing a 2 tonne trailer ( regradless of what you are towing with) is a realtivly straight forward thing and well within the realms of practicality as loong as the trailer towed is well withing the manufacturers towing capacity.

As soon as you say the words "off road" towing a 2 tonne trailer becomes a whole lot more a serious and complicated matter.

The manufacturers published carrying and towing capacities are written for " smooth improved pavements"...beyond that the carrying and towing capacities have to be considerably reduced...particularly considering the modern published towing capacities are generous and optomistic to say the least.

Halving the published carrying and towing capacities is far from unreasonable for off road use....if the manufacturer has a particularly generaous on road towing capacity...1/3 published is far From unreasonable.

There are endless pictures and stories of vehicles "towing within capacity" bending and breaking bits towing off road.

The back sitting down is the least of your worries.

If you need a WD hitch or some sort of rear load booster device ...ya probaly should not be towing it off road.


cheers

Tony

Have you worked out how much weight you have behind the rear axle? A 2000kg van on an empty Triton without a WDH will most likely be right on the limit. When you start loading up the rear, things get a lot worse. Chassis damage on cab/chassis utes, be they single, extra or dual, comes from the unrestrained load behind the rear axle falling when the wheels drop into depressions in the road. All of this falling material generates forces well above the static weight and gives the end of the chassis a hell of a thump down rocking it on the axle and lifting the front. The further the weight is back from the axle, the greater the leverage will be on the end of the chassis. A similar thing happens when the front wheels drop down. The rear end of the chassis behind the rear axle has to be heaved up instantly placing tremendous stress on it above the axle or often slightly in front of it.

No amount of springs, shocks or air bags are going to change a thing. They just make an overstressed chassis sit up a little higher. Excess weight must be either transferred forward to the front wheels with a WDH, moved further forward in the car or removed completely from the car.

Put a bit of thought into it while deciding what to do. If you car is too far down at the back and is not incorrectly loaded, i.e too much weight at the back and too little in the cabin, then lifting it with a WDH is an approved remedy. Any other method will always leave a question mark hanging over its reliability. You might get away with it or you could easily join the countless others who haven’t. Only time will tell.

OP posted "I intend to do a bit of "off road" travel".
For many Off road means dirt roads for others it's extreme tracks or completely going bush.
For On Road and Dirt Roads I'd personally be using a WDH and removing it for extreme terrain.
NOTE: Mitsubishi recommend that a WDH be sued when towing with a Triton.
Ozjohn.

All you need to do is upgrade the springs and shocks to suit what your towing avoid air bags because the might cause problems with this type of vehicle .Then if your vehicle is a twin cab I would be very concerned about putting to much weight on the rear and look at getting the chassis strengthened behind the back of the cab because that's where most twin cabs are prone to snapping chassis. There are lots of pics around with these light weight utes with broken chassis sorry to say but the manufactures have the gross combined weight way overrated for what these vehicles are actually capable of carrying or towing.

Tony, a quick scan of the responses above appears to completely overlook a key reason for using a so-called Weight Distribution Hitch. When you load up the tail of a vehicle which has been basically designed to run flat i.e. Level , with drooping tail and therefore nose-up at the front, the angle of the front suspension components, specifically, the king pin angle ( the king pins being the near vertical axies of the steering) is significantly altered and consequently the vehicle can become difficult - read dangerous - to steer.
Try driving a ute with one tonne of sand in the back end of the tray and the nose up on the air and see how dangerous it is. Must get the vehicle to ride horizontally along with all the other things one must do correctly e.g. Keep the loads within allowable spec.

Hi Tony

I would fit a Mitsubishi WDH (rated to 250 kg ball weight), and if there is any sag, add a set of King springs or similar.

Worked for my Pajero.

Don' t have to worry about taking off HR WDH gear when 'offroad'.

Cheers - Phil