Montie   Thanks for that. 

As I expected, the manufactures' engineers have some sort of black magic formulae, kept secret from we the great unwashed. Cynical me!

Thanks for the offer, but I am only seeking understanding.  I have no problems with my 1996 4.2EFI GQ Patrol.

The most common manufacturer upgrade in rear axle weight capacity occurs on some of the more modern variations of the large American utes.

They tend to convert the housing to dual wheels and quite often a heavier design of outer bearings.

The old model designation was a little clue with Fords

F100 was rated at 1 tonne F150 was 1.5 tonne then you got into the F250s which could be either single or dual wheel rear with different ratings in the USA.

This may or may not have applied in our country.

For example, with the well reported new Dodge Ram or just Ram as it is now known,it could probably be easily upgraded with a wheel and tyre modification or to really push it they might even have available a heavier rear axle option that might fit. In the USA they have gear that we might only dream about when our wallet is so full it becomes painful.

In the USA they dont muck around with this sort of modification because you would just by a Ram 250 for example or the next model up the weight tree.

With the correct engineering certificate and a pocket full of folding stuff almost anything is possible.

In days gone by we had in Aus a plethora of F100 fords which consisted of differing mechanical components.

Some people used to think they were indestructible and quit often would overload the rear axle.

As a result the rear axle housing would fail, generally around the area where the axle tube joined the centre housing,

I have seen all types of abominations of bits of steel welded along the axle tubes and various other add ons to support the weak structure of the tube.

Of course the axle tubes were fine if you only loaded to the specified weight and if you were tempting an overload then drive very carefully on our less than adequate roads if we compare our road infrastructure to the USA.
Many F 100s had heavier diffs and springs etc fitted for what we might call off highway work. Some fire authorities used those utes with some modifications as well for extra weight, I believe.

With many of our mid size utes and SUV wagons the weight restriction is for the reason of vehicle stability rather than the axle housing snapping in half.
We see this when the vehicle modification companies upgrade springs and shock absorbers to gain an upgrade.
The argument would be that the handbook of vehicle specifications states the rear axle load as standard and this will be the base of the argument of the modification that doesnt give you any increase,
I dont want to get into an argument as when towing a conventional caravan the ball weight specification of the vehicle comes very importantly into play.
If we look at the vehicle modification without considering towing then the popular SUV once modified can carry the mining personnel in the back and still have the bars and spare wheel etc and can and does comply with the law and with insurance company requirements.

I dont think welding a couple of pieces of heavy angle iron along the diff axle tubes will pass the test today. Having said that I have read adverts somewhere where companies do build or supply heavier housings for special purposes.
I have seen claims of some of the rear track widening kits for the very off road and industrial farmers and mining utes, do increase the load capability. Again this modification is sought after by the likes of some fire authorities when using these vehicles for off road fire control.

Montie has covered how these figures and specifications are met but with the correct engineering there are lots more possibilities.

A great example of this comes from the Street Rod fraternity who can build and have registered almost anything BUT, these car builders and their cars modifications must pass the scrutiny of engineers qualified to assess these vehicles.

I hope this covers it Cupie

Cupie wrote:

---

Thanks all for your replies & expertise.

As I previously indicated, I have no need/desire to increase Axel load rating for my ageing tug.   It has 288,000km travelled, around 95% towing the van, all on bitumen.

It is extremely difficult to get the numbers for a 1996 GQ TB42 efi (Petrol) Patrol.  It seems that according to several sources that it has a higher tow capacity than the TD42 GQ   (2.8t v 2.5t).  In any case my Jayco is comfortably under both but it has a high  towball weight of 271kg (hitch capacity 350kg - perhaps due to in part to the gas bottles on the A frame & a front boot as well as a front kitchen) & ATM 2334.   Haven't bothered to measure the rear axel weight as I have no reference figure.

 

BTW .. I have had continuing problems with my passenger side rear axel bearing weeping.  I have had various 'experts' look at it over the years including both inner & outer seals replaced several times & the bearing replaced on two occasions  .. the bearing is destroyed in getting to the outer seal.  The latest try seems to have fixed it.

The latest Patrol specialist diagnosed it as having had the axel 'skimmed' to just below specifications (I think that this happened when it was first looked at, at 80,000km).  The solution was to install a selected second hand axel, bearing etc. and grease the sealed bearing using a special needle nib on the grease gun.   No sign of a weep after 15,000km.  

I did from time to time wonder if the cause was an overloaded rear axel.

 

Once again, thanks for your input.

---

 If we knew your problem was a leaking axle seal then someone may have suggested a *speedy sleeve*.

The left hand side often is the axle that leaks first because it is in a lower position due to the camber of the road.

Sometimes just lowering the oil level in the diff by a tiny bit will fix it.

Many servicemen fill the diff and then it becomes a contest to get the level plug back in before the oil has actually found its true level thus resulting in a slightly overfill.

Leaking sealed bearings are usually the cause of the Chinese factory where they are made.

Also heat can damage the seal in a sealed bearing. 

Heat may be generated with something as simple as a dragging brake or it may be a symptom or overloading or high loading of the rear axle.

The weight will transfer a larger proportion of itself to the left hub due to the roads camber again generating more heat in that bearing,

You seem to be on top of it and that is a good thing.

Chris   ..Thanks for that.

Where do you get your figures from?

Some time back I did lots of searching with no success.

What are the factors that cause a 271kg  ball weight result in 400g on the rear axel? 

I assume it is something related to 'lever action' & distance from ball to 'fulcrum point' of rear axel.

 

BTW, I have always used a HR WDH that has the effect of correcting the rear end sag when the van is connected.  It was fitted by the people that purchased the van from.

cheers 

Thanks Stephen..

Easy to demonstrate on a weigh bridge.

Compare connected and disconnected axle weights with the WDH on the same vehicle.

Are We Lost wrote:

---

I think Yobarr just uses approximations based on experience. To accurately calculate what load the van adds to the rear axle load you need three things:

TBL = Towball load
WB = Wheelbase (use mm for accuracy)
OVH = Towball overhang (distance from rear axle to towball)

Rear axle load added by van = TBL x (WB + OVH) / WB

For your Patrol, I found a figure of 2970 for wheelbase. You will need to measure your towball overhang. I did a calculation and tried a few different figures to arrive at Yobarr's estimate of 400kg. I suspect that may be close enough, but marginally overstated because it would mean a towball overhang of 1420mm. I thought the Patrol would be less than that. Anyway, using that hypothetical figure here is the calculation:

Rear axle load (400) = 271 x (2970 + 1420) / 2970

If you change OVH to 1200mm it comes out to 380kg, so not a huge difference.

Because this only looks at the difference when connecting the van, not the actual axle load, the formula works regardless of how your load is distributed in the tow vehicle. To determine how much weight is lifted off the front wheels, just subtract the towball weight from the rear axle loading calculation ... in your case it works out to 110-130kg.

-- Edited by Are We Lost on Sunday 17th of July 2022 12:11:53 PM

---

 Just measured the OVH  and it is 1200

 

Thanks again to all.

-- Edited by Cupie on Sunday 17th of July 2022 02:32:21 PM

Cupie wrote:

---

Chris   ..Thanks for that.

Where do you get your figures from?

Some time back I did lots of searching with no success.

What are the factors that cause a 271kg  ball weight result in 400g on the rear axel? 

I assume it is something related to 'lever action' & distance from ball to 'fulcrum point' of rear axel.

 BTW, I have always used a HR WDH that has the effect of correcting the rear end sag when the van is connected.  It was fitted by the people that purchased the van from.

cheers 

---

 Hi Cupie. The axle ratings are among my records, and as Stephen suggested, the 400kg added to your rear axle was simply an estimate, intended to illustrate a point. There is actually one greatly over rated vehicle that has TBO of better than 50% so a 350kg towball weight puts over 520kg onto its lightweight rear axle, but we won't go there! Cheers

Ivan 01 wrote:

---

How was that Mike.? 

---

Poor, no better than Yobarr's  - I don't think either of you properly understand what's happening with a weight distribution hitch.

>provide a more rigid transfer of this extra weight

Whatever is "a more rigid transfer" of weight? and what units is it measured in?!

Is there a proper mechanical engineer in the house?

Ivan 01 wrote:

---

Oh just one thing Mike, I fully understand what happens with a WDH. No one has to be a Mechanical Engineer to know how they work.

---

Ivan: there is a very, very old adage in engineering and it is:

If you can't explain it then you don't understand it.

Mike Harding wrote:

---

Ivan 01 wrote:

---

Oh just one thing Mike, I fully understand what happens with a WDH. No one has to be a Mechanical Engineer to know how they work.

---

Ivan: there is a very, very old adage in engineering and it is:

If you can't explain it then you don't understand it.

---

 The problem we have, Mike, is that trying to explain it in a way that most readers can understand is an impossibility. Different levels of comprehension by readers, along with very little understanding of basic physics by some, make the task very difficult, which is why I have to generalise. When I first joined the forum and posted that a WDH increased a van's weight I was criticised and shouted down left, right and centre by many 'senior' members, but I stuck to my guns and continued explaining, on a regular basis, how a WDH actually does work until now it is generally understood  that a WDH takes weight off the rear axle (NOT the towball) and puts some of that weight back onto the car's front axle, from where it came, and also it puts some weight onto the van's axle group, thus increasing the weight of the van. Total weight of car has decreased, Total weight of van has increased, Total weight (GCM if you like) stays the same. Believe me, I can sit here for hours and explain in great detail how a WDH works, but unless the reader actually WANTS to learn, rather than argue, I'm wasting my time. However, rote learning does seem to work eventually. Slowly but surely many members are realising that, with weights, I know what I'm talking about, but because of continual interference by others who who know little, understand less, and have no interest in learning, several members have chosen to contact me by PM to get help with their weights. Indeed, I have also visited them to help.  Cheers

-- Edited by yobarr on Sunday 17th of July 2022 05:41:02 PM

Ivan 01 wrote:

---

Mike Harding wrote:

---

Ivan 01 wrote:

---

Oh just one thing Mike, I fully understand what happens with a WDH. No one has to be a Mechanical Engineer to know how they work.

---

Ivan: there is a very, very old adage in engineering and it is:

If you can't explain it then you don't understand it.

---

 Well it will be interesting next time someone might offer help with a fridge problem. Where is a refrigeration engineer when you need one.

Do we wait until our mechanical engineer comes on to help someone with a wheel alignment problem or will a mechanic suffice.

I have worked along side quite a few mechanical and civil engineers during my career and I have never heard that said however I take it on board.

I will wait to hear the explanation from a mechanical engineer if only to check myself on knowing how a WDH works.

I wonder if someone who has the title of associate (degree or Diploma) of mechanical engineers will qualify to explain.

 

---

 Hi Ivan. I'm surprised that after all the explanations that have been given regarding how a WDH works, along with actual weighbridge test results etc, you still seem hesitant to accept the simple facts. The fact that many retailers of these pieces of equipment have little idea dies not help.  Perhaps you could Google "John Cadogan. How a WDH works" or similar and if, after watching the video you still do not understand there is little more that can be done to help you. John is, as explained in the video, an engineer with much experience. Cheers

 

P.S  "Weight distribution and load levelling hitches for heavy towing" John Cadogan is the video you need to find!

      If you're pressed for time the important stuff is between 13th and 14th minute and between 17th and 19th minute. He explains only the basics so as to make it as easy as possible for it to be understood by many.

 

 

-- Edited by yobarr on Sunday 17th of July 2022 07:36:27 PM

I see there are a few posts with explanations on how a WDH works, and interspersed in those are the opinions on whether they are good or bad. But they are mostly on what they do, and not a lot on how, which is what Mike was asking. Like Ivan, I will skip the discussion on the pros and cons .... for now. But I have taken a different tack to the explanation method, and kept in mind Mike's request for simplicity. I hope I haven't gone too far.

But first, I believe that a sagging rear end is just an easy visual signal that something is wrong, and it is weight on the wheels that need attention. Its the weight that matters, not the level. But for simplicity I have focused mainly on levelling in this explanation. Also I have not tried to use the correct physics terminology ... weight, mass, torque, force, load. My high school physics is now forgotten.

Imagine you are standing at the back of your tow vehicle with van attached, looking at sagging rear end. One of these days you will do something about it. You happen to see a couple of bars made from spring steel lying there at the campsite.

Being a fit muscular fellow, you think one of these bars might come in handy for a workout. At the back of the car, you find there is a spot you can push it in from the rear and it seems to lock in place. It feels rock solid and has effectively become an extension of the car. Onto your workout, and with some effort lifting the bar you can see that the car body lifts up a bit at the rear and the whole rig becomes closer to level. If you had scales you would see the weight on the front wheels is now slightly more, and the weight on the back wheels is less.

Also, if you used a tape measure you would see that the end of the bar you are holding was raised more than the body of the car. Or to put it a different way, the leverage enabled you to lift the rear end further than if you had tried at the rear bumper. I will come back to this point.

You note that there is a bracket on the caravan drawbar you can attach this bar to. Being an innovative fellow, an idea starts to form in your mind. Maybe this will help with the levelling. So with a supreme effort you manage to lift the bar a little more and hook the end of it onto the bracket. While you are recovering, you check and notice that the sag has returned a bit, but not as much as before. Just for fun you stand on the drawbar and bounce a bit. You realise that it feels a lot firmer than you expected it to. It's a bit puzzling. The bar is still lifting up the back of the car, but the end of that bar is resting on the drawbar bracket and is pulling the drawbar down harder onto the towball.

Why does this work? Surely if the bar is lifting the rear end up, but that very same bar is pulling the drawbar down, they will cancel each other out and you will achieve nothing.

 

Well, its late now so I think I will call this the first instalment and write the rest in the morning. If someone wants to have a go, please do.

-- Edited by Are We Lost on Monday 18th of July 2022 01:58:52 AM