DMAX rear airbag suspension assist experience

Submitted: Tuesday, Oct 19, 2021 at 20:41
ThreadID: 142736 Views:6373 Replies:11 FollowUps:30
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Hi all, we want to hear good or bad experiences from Isuzu DMAX owners who have fitted upgraded suspension with airbag assist for the rear leaf springs. I personally doesn't like airbags because to my mind they apply force in the exact opposite direction for which the section of chassis over the rear axle was designed for. But our quest for a CAPABLE and DURABLE suspension without airbags, for extended off-road and outback track touring at close to max weight in our MY2015 4x4 dual cab DMAX, has failed. We started with a Dobinson suspension upgrade with remote-res shocks all round and +400kg constant rear leaves which was comfortable and worked well until we snapped a leaf spring front eye in the middle of nowhere and had to creep 300ks back to Newman in WA with the rear axle rachet-strapped in place. At Newman, the most convenient and quick spring replacement option was an Old Man Emu spring pack each side. With the choices of coming back to +300 or going up to +600, we went +600, which might have been the wrong choice with hindsight. As per a Forum thread earlier this year, 2 years on from putting the heavier springs in (they also rode well, given that the car rarely goes anywhere unladen and without a camper trailer on the back) we cracked the rear axle housing on both sides, from the outer welds on the spring perches around the back of the housing. We had a new housing and new wheel bearings installed but were told the same thing would happen again unless we changed something (the stiff springing may have contributed to the compression stress factures of the axle housing). The mechanic who replaced the housing and a suspension company he recommended have said we should fit Tough Dog +300 springs supplemented by Tough Dog air bellows run at relatively low pressure to level the car when fully loaded with camper on back. Idler Chris, one of the respondents earlier in the year, also suggested we switch to a similar setup. We've also dropped the old housing off at a diff specialist who builds axle housings for drag cars. He's going to see whether it might be worth retubing (he wasn't impressed Isuzu housing is welded tube) and bracing.
Anyone else have any ideas?
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Reply By: Frank P (NSW) - Wednesday, Oct 20, 2021 at 10:10

Wednesday, Oct 20, 2021 at 10:10
Congratulations on getting yourself out of a pickle.

However, everything you've described suggests to me overload for the conditions. Max weight, towing, broken springs, broken axle housings.

What are your driving and tyre management habits? - because they sure as heck have a bearing on this issue as well as suspension and vehicle capability.

What is the CT's towball downforce? I ask that because that has to be added to the load in the vehicle - has that been accounted for? Also, there is a multiplier effect of the downforce on the rear axle load, which depends on the wheelbase of the vehicle and the distance between the rear axle and the towball (overhang).

An example:
Wheelbase 3000mm. Overhang 1200mm. Ball weight 150kg.
Divide overhang by wheelbase, 1200/3000 = 0.4
Physics dictates that the load on the rear axle imposed by the ball weight is not 150kg, it is 1.4 x 150 = 210kg. (And the front axle will have 0.4 x 150 = 60kg taken off it.)

FWIW I agree 100% with you in regard to air bags assisting leaf springs - for the sake of the chassis, leave the airbags out.

A reinforced/re-manufactured rear axle housing will undoubtedly help the Dmax axle issue - you are not the first to have suffered that failure, but perhaps the first to have suffered two! You have said that the Dobinson upgrade was satisfactory up until the failure of one spring. Perhaps your best option may be to return to the Dobinson configuration you had and, without being personal LOL, try to lose some weight.


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Follow Up By: Member - Mal and Naomi G - Wednesday, Oct 20, 2021 at 11:30

Wednesday, Oct 20, 2021 at 11:30
G'day FrankP, you're right, weight is undoubtedly the problem.
Trouble is, most of the weight is fuel and water.
We're going through our set up taking out everything that is not essential but that's only saving a few kilos here and there. I drop tyre pressures to 28psi rear and 24psi front and camper on corrugated dirt and work down from there if I needs be. We don't attempt to find the 'sweet spot' above 80kph, preferring to pick our path and take it easy.
The calculation on draw bar length is interesting, it's a standard H/D Isuzu bar with standard length hitch fitted with off-road coupling, but on long distance treks we carry 2xjerries of fuel/water on the camper drawbar which would put ball weight at 160kg + (camper weights 1250kg bare but probably up to 1600kg with 120lts water/food/bedding/clothing etc). Dobinson spring break was interesting, discolouration in metal at break suggests slag or some other impurity was caught up in steel during manufacture. A spring specialist who looked at it said it happens and you can't tell 'til the spring leaf fails. It did fail some 130ks after a driver error incident by me being a bit cocky, where we came off the top of a Canning Stock Route sandhill and dropped into an unseen crater somebody heading the other way with hard tyres had dug in the sand.
All the 'experts' are pushing me towards airbags but I'm yet to be convinced.
Strengthening diff housing if that proves possible and changing springs again, I understand, but pressure on the chassis where it's not meant to take pressure I don't understand.
Thanks for your reply.
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Follow Up By: RMD - Wednesday, Oct 20, 2021 at 12:35

Wednesday, Oct 20, 2021 at 12:35
G'day Mal.
Those "experts", do they travel remotely and use vehicles outside their suburbs? If not then they are not experts, only experts in retail.
I would avoid airbags on a Dmax chassis, although I did use them on a HJ61 Cruiser to restore height and allow some "up" travel to be there. Having the ability to ABSORB is half the problem solved.
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Follow Up By: Member - Mal and Naomi G - Wednesday, Oct 20, 2021 at 14:04

Wednesday, Oct 20, 2021 at 14:04
Yep, agreed FrankP.
Hard to get factual info on airbags from people with no commercial association, who have put them through what we will put them through.
I know they will cop a pounding and transfer some of that to the chassis, which worries me because the bracing on the DMAX chassis over the back axle is designed to stop the bend in the chassis from trying to straighten out when the spring pack flattens under load and pushes the spring hanger backwards. Air bags will try to increase the bend in the chassis rail by pushing up from underneath - the exact opposite of the design criteria.
I hate it when a 20 something guy behind the jump at a city suspension mob says 'None of our customers have had a problem with them (airbags)' and you know they're going under overloaded tradie utes to stop the bum dragging and the only rough stuff they see is 20 metres of building site, not 100s of ks of unrelenting corrugations. That's why I was hoping for first-hand experiences to try and gauge the risk of bending the chassis.
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Follow Up By: Member - mechpete - Thursday, Oct 21, 2021 at 14:03

Thursday, Oct 21, 2021 at 14:03
bent chassis comin up with air bags
cheers mechpete
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Reply By: TrevorDavid - Wednesday, Oct 20, 2021 at 11:25

Wednesday, Oct 20, 2021 at 11:25

Can’t help with your problem, but the below link is to a Isuzu forum. Hopefully you may find an answer there. You could even ask the same question. Good Luck, hope you sort it out.



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Follow Up By: Member - Mal and Naomi G - Wednesday, Oct 20, 2021 at 11:31

Wednesday, Oct 20, 2021 at 11:31
Thanks TrevorDavid, I'll put my question up there too.
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Follow Up By: RMD - Wednesday, Oct 20, 2021 at 12:39

Wednesday, Oct 20, 2021 at 12:39
Many on that site have broken things most people never do and accept failures but seem to not admit they had problems. Hard to get a true response from a sound base of actual problem solving to be able to act on it.
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Follow Up By: TrevorDavid - Wednesday, Oct 20, 2021 at 19:53

Wednesday, Oct 20, 2021 at 19:53
Read my post again RMD

He may get an answer, he may not, nothing wrong with trying.


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Reply By: Idler Chris - Wednesday, Oct 20, 2021 at 18:01

Wednesday, Oct 20, 2021 at 18:01
Hi Mal and Naomi, Like you I have broken 2 axles housings so far. I do not believe anyone has the definitive answer as what is the best solution for a pre 2020 D-Max. It should not be a problem with the current model D-Max as the axle housing is substantially bigger. My current solution is as a result of my own extensive experience, my four wheel drive specialist, and a very knowledgeable person from Lovells Suspension.
Also I have noticed that the welding on new axle housing I brought from Isuzu earlier this year is different from the old axle housing. On the old axle housing the cracking always started at the end of a weld line near the U bolt. The replacement axle has a bigger weld so without any other changes Isuzu may have fixed the problem for the current model. Unfortunately the axle of the current D-Max will NOT fit the previous models.

The problem is that the axle cracks through metal fatigue. The factors that are involved are;
1. weight on back axle
2. spring stiffness
3. shock absorbers
4. bump stop
5. tyre pressure and construction
6. road conditions - corrugations and holes hit at speed
7. speed
8. time spent loaded and on bad roads are much higher than the average D-Max.

When the wheel hits something hard enough that it makes it move suddenly like a corrugation or pot hole, a shock is sent to the axle housing when the suspension maxes out. The greater the weight on the back axle the greater the shock. Spring stiffness and shock absorbers will affect the shock to the axle depending on their quality and suitability. The standard bump stop is solid rubber and provides very little cushioning. Tyre pressures and construction will affect cushioning. And the greater the speed being driven the greater the shock to the axle.
Taking these factors, this is what I have done based on my experience.
1. weight on back axle. We are well aware that weight is the issue and have reduced the weight as much as possible.
2. spring stiffness. I broke the the first axle housing on 300 kg springs and the second on 600 kg springs. I am not sure but I think the 600 kg springs may transmit some shock to the axle housing before they are maxed out. I currently have a Lovells GVM upgrade to 3600 kg and it is with 300kg springs.
3. shock absorbers. I am using Lovells shocks but obviously the better the shock absorber is, the likely it is to be the least shock on the axle housing.
4. bump stop. The standard bump stop provides little cushioning as it is hard solid rubber . I have removed the bump stop and replaced them with Mr Airbag Man airbags. I pump them up to raise the back wheel arch by 1 centimetre which in my case equates to 30 psi. The idea here is to replace the sudden jarring when hitting the bump stop with a more controlled stop. So while the airbag will carry some of the weight is it is installed to lessen the shock that would occur with a bump stop. A secondary benefit is that you should only need 300 kg springs and not 600kg springs. The axle is reinforced above the bump stop so I do not think this is an issue by installing an airbag. The chassis on a D-max is second to none, so the usually warnings about airbags breaking chassis do not apply to a D-Max IMHO.
5. tyre pressures and construction. Tyre pressure should reflect the the terrain and speed you are travelling. When offroad, travel at the lowest tyre pressure that the conditions dictate, this way the tyre can absorb some of the shock. Heavy construction also very helpful in absorbing shock. My tyres are 265x75x16 with a load rating of 123 and speed rating of Q, which is one size up from standard. The higher sidewall at 75 adds a bit of cushioning. I also usually use mud tyres.
6. road conditions are what they are.
7. speed. Because of the load we carry the distance of axle travel downwards is about half that of an unladen vehicle. The faster you drive the greater the chance you will max out suspension travel, and with a greater force when you do max out.
8. You can solve the problem completely by sticking to the black top. That is unacceptable to me, I travel dirt roads when ever I can.
As per my previous posts I am happy to talk with others if that helps. My number is 0419846292 but I have left the madhouse that is Victoria and I am in Perth which is 3 hours behind the eastern states.
What other people think of me is none of my business.
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Follow Up By: Member - Mal and Naomi G - Wednesday, Oct 20, 2021 at 22:13

Wednesday, Oct 20, 2021 at 22:13
G'day Idler Chris, welcome to WA.
Like you, sticking to the blacktop is unacceptable to us, so we too are exploring suspension options for our DMAX. Our greatest weight is fuel and water, so not a lot of scope to trim there for remote outback touring, keeping safety margins in mind.
We run the same size tyres as you, BF Goodrich KO2s and my speed controller (Naomi) has vowed we will travel more slowly than we already do now.
On corrugations I start at 28psi in the rear tyres, 24psi in fronts and CT and work down from there if needed - I have a habit of walking around the outfit touching each tyre whenever we stop, it's a great way of picking up if you've got a tyre going soft because you can easily detect the temperature difference.
I've checked out a current model DMAX cab chassis and the back axle housing looks like tube is up to 3.5 inch OD with different spring plate and top plate to accommodate bigger diameter tube, interestingly the new bump stop is much smaller than ours. Diff housing is significantly braced but interface between axle housing and diff housing is also different, so you are right, new axle housing isn't a simple swap option.
The replacement 2012-2020 axle housing we bought had a different part number to the original and, like yours, had extended spring perch welds, but otherwise was identical.
I'm hoping Final Drive in O'Connor can rebuild our cracked housing. They specialise in rebuilding Ford 9 inch diffs for drag racers and use a thick-walled hydraulic tube that is 4mm smaller OD than the Isuzu axle tube, but much stronger because it's a thicker wall and is not welded along one side.
The drama is welding the new tube into the banjo housing in a way that doesn't simply transfer the weak stress point from the outside of the spring perch to the inside ends of the axle tubes. Final Drive is looking at a possibility of welding bracing under the housing running from the banjo housing out along the axle tube to try and overcome this. If you are interested, I can let you know more about it when they get back to us - we've left the cracked housing with them to have a play.
We're also looking at changing the +600 rear springs out for something less severe, although we don't know what yet. The +600 didn't ride hard, but I noticed more rear body roll with the +400 springs we had in before the +600. +400 seems like the best option, we just had a bad experience with what looks like a bad spring previously.
It goes against the grain, but I am slowly coming around to running low pressure air bags as a softer bump stop option as you are.

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Follow Up By: RMD - Wednesday, Oct 20, 2021 at 23:04

Wednesday, Oct 20, 2021 at 23:04
Chris, Perhaps Mal too.
I didn't know you have broken two axle housings or is it one housing in two places?
You mention a bigger weld on the new axle, does it spread the stress over a wider area but same tube size?

The axle tube does crack as a result of metal fatigue, but that is caused by localized flexing at that point. No flex or not much flex means less likely to fatigue.
Undoubtedly the heavy loading is a contributing factor but the axle doesn't simply crack with the load on it, only when flexing with that load “past” a certain degree does a problem arise.
I agree with the numbered points you have shown.
Weight on axle yes,
Spring stiffness is a difficult thing to quantify, a stiff spring may not deflect much and have less initial curvature and no appreciable ride height. Others may be more compliant and begin with more ride height and are far more compliant. That I like!
Shock absorbers may resist initial movement very abruptly, not so good, others are slower to resist and therefore kinder to suspension. Only a test graph from a manufacturer would reveal that. Again hard to test/gauge by the average user.
Bump stops. You may be surprised how much the OE bump stop squashes when impacted and they don't have much ability. Most folk rubbish them. An airbag, in my opinion has VERY LITTLE internal bump stop and so little ability to finally absorb shock. Unfortunately, the airbags reduce the overall travel simply because they have a top plate and a bottom plate which all takes up travel room. I used some on my cruiser and was acutely aware of the LESS travel they caused. They had practically NO bump rubber action at all if bottomed. See how far you an compress them with no air inside. You may be shocked. Sales hype is the opposite!
Have you actually seen the internal bump stops in an airbag. Best to make sure you really know their limitations, other wise the same problem is still present.
With the available dimensions of the whole setup, ie ride height/travel UP and down what percentage of up travel do you have when loaded? When fully loaded for travel, 1/3 down and 2/3 up travel of whole distance would be desirable so as to begin to be able to “absorb” without undue stresses. If there is isn't around 2/3 of total for upwards travel then the same situation remains as before. For my cruiser I made sure I had that specifically, so bottoming of the axle didn't happen and shocks could catch movement during compression. I did it because the bags had NO detectable bump stops although I was assured by the Air Bag Man they did.
With a raise of 1cm which is only 10mm and airbag dimensions taking some of the up travel, it would worry me.
Isuzu are strange in a way. Mine said 80mm clearance to bump stop when new, As new, no load mine was 52mm clearance. I changed it to 120mm before load. Then I had up travel to use.

5,6,7,8, are all manageable situations and vary.

With regard to axle movement, most bumps are felt at an angle to the axle, ie, a line leaning backwards, no direct vertical unless stopped. Any impact is resisted by the suddenness of the shocks and compliance or lack of of the springing. There is also the mass of the whole diff housing and internals. All causes an axle stress load before the axle actually moves and so localised stress at the weld area. Some vehicles have large dia front eye bushes which absorb some suddenness. My 2011 front eyes are small and simply transfer much of the shock to the body. If felt there, the axle tube must be feeling it too. What size front bushing is in the later models? I haven't checked them to see.

I simply place importance on springing and shocks and travel height with sufficient upward movement to actually work. In the Isuzu you can't change the axle much, apart from gusset bracing in vital areas, so other component action and dynamic operation become important considerations.
If the axle tube is “light on”for the task then only strengthening it will overcome the flex and failure issue. The above assists the life expectancy.
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Reply By: Idler Chris - Wednesday, Oct 20, 2021 at 23:05

Wednesday, Oct 20, 2021 at 23:05
Hi Mal,

I have had 4 reinforcing strips welded to my axle and have now done about 20k mostly off the black top. I am living less than 5 minutes from Final Drive and would be more than happy to take my vehicle around there and let them/you see what I have done and I can also explain why we did what we did. More than happy to catch up and compare experiences.

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Reply By: Gbc.. - Thursday, Oct 21, 2021 at 07:53

Thursday, Oct 21, 2021 at 07:53
I have the new dmax (bt50) with boss airbags for towing. I have had them on numerous twin cabs and done extensive ‘outback’ travel. My first set was in 2003 on a hilux. Amazingly I haven’t bent any cars to date. Set up with an uprated spring pack they are a good way of adjusting the rear end. I make sure when I’m loaded to near gvm that there is a definite slight sag in the rear, meaning the leaves are fully engaged. I see factory cars with bags so inflated they look like a lift kit some times. When I get proper off-road I let them down even more but not so far as the springs start topping out. There is a bit of trial and error. If you have plenty of coin I think an in cab adjustment setup would be nice - I just use a bicycle floor pump though. Riding around with just my ally canopy and XT (heavier duty) factory springs, I run around 5 psi. At GVM it will be 35 odd. They handle corrugations better than leaves and give a smoother ride. The shocks get a workout though, so they may require attention. Done judiciously, bags are great. Unfortunately they get a bad rap from those who have expected too much. I am always within factory gvm - just.
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Follow Up By: RMD - Thursday, Oct 21, 2021 at 10:11

Thursday, Oct 21, 2021 at 10:11
Just to be clear, with airbag pressure and upward suspension/axle movement, you mean Bottoming instead of Topping out don't you?. With Motor cycles when airborne the forks extend fully and the slider and axle go downward until the capture hits the TOP of the piston on the fork tube. ie, called topping out. Actually the opposite to hitting maximum compression and being at the bottom of travel. With 4wd and airborne, the rear axle will extend to shock limit and they Top out then with coils, airbag or leaves.
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Follow Up By: Gbc.. - Thursday, Oct 21, 2021 at 11:22

Thursday, Oct 21, 2021 at 11:22
Correct, yes - the springs hit the 'imaginary bump stop' if there isn't enough pressure in them. That is Bottoming out?
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Follow Up By: Member - Mal and Naomi G - Thursday, Oct 21, 2021 at 12:05

Thursday, Oct 21, 2021 at 12:05
Hi Gbc,
Thank you for sharing your air bag experience. I seem to be picking up that people who use them at low pressure to assist the leaf springs doing the primary job of suspending the vehicle, don't have too many problems, but those who run them at higher pressures to take over the role of the springs at higher loading weights are the ones we hear about who break or bend chassis rails.
We travel within the GVM, but like you, only just, and it seems likely the axle housing failures are caused by a combination of certain factors, including design and thickness of construction material used in relation to advertised GVM, frequent high weight loading usage on corrugated back roads and 70,000 + kilometres - essentially, time for flexing of the axle housing to set up a metal fatigue stress fracture.
Main-road tyre pressures and speed would no doubt make the problem appear much earlier.
Your Bt50 has a much heavier rear axle housing and diff carrier than our My2015 model. Interestingly though, Isuzu only raised the GVM by about 100 or 150kg from memory, but looking at the rear axle assembly under yours, compared to ours, you would say yours was capable of carrying half as much again.
Mal and Naomi
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Follow Up By: Gbc.. - Thursday, Oct 21, 2021 at 12:24

Thursday, Oct 21, 2021 at 12:24
Yes I think history will show that your issue is simply poor design rather than anything you've done wrong which is unfortunate because now you have to resort to masking the symptoms rather than fixing the problem. I wish you all the best with it. In a perfect world we could set up the perfect leaf set for a fixed weight, but add in changing load states and road conditions and I like being able to make adjustments accordingly. Be warned, if you unhitch the trailer and leave the bags up high, the rear of the ute can easily take flight over small bumps......they need attention as part of a system.
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Follow Up By: RMD - Thursday, Oct 21, 2021 at 15:33

Thursday, Oct 21, 2021 at 15:33
It isn't the springs of any sort which bottoms, it is the axle hitting the chassis and that causes flexing of all related bits. My concern with airbags is: of the available upward travel, airbags take up some of that travel, Yes, they do assist, but the total upward travel available to absorb the suspension action under load is "reduced", ie, not what it could be. Flight over bumps with bags pressured, is because the down travel is already "down" and there is no droop left fr tyre tracking to occur, so it leaves the ground with no controlled tyre grip on anything.
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Follow Up By: Gbc.. - Thursday, Oct 21, 2021 at 15:52

Thursday, Oct 21, 2021 at 15:52
I haven’t measured but I’d guess a compressed boss bag dimension would be similar to the bump stop (75mm odd?) they replace. They also have very thick rubber which acts as a bump stop. The older bags were flimsy in comparison. I run much less pressure than I used to. Your point is valid for an overinflated bag for sure, but they are designed to work through a normal suspension stroke at proper working pressures. Those pressures just need adjusting all the time as loading changes. They are by no means the best answer to Ute loading and they aren’t for everybody that’s for sure, and could certainly cause damage if not used judiciously.
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Follow Up By: RMD - Thursday, Oct 21, 2021 at 19:44

Thursday, Oct 21, 2021 at 19:44
Yes the compressed bag may be similar height to the bump rubbers but the airbag when compressed has almost NO RUBBER COMPRESSION aspect, just suddenness. At least the bump stop at that point is where it begins to deform and absorb and further decelerate the axle.
Has anyone who has airbags actually seen the claimed internal bump rubbers. I know my Airbag Man ones had zilch and just once it bottomed and it is then I made changes to NOT have it happen again. A combination of suitable springing and shocks which controlled.
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Reply By: Member - Core420 - Thursday, Oct 21, 2021 at 16:51

Thursday, Oct 21, 2021 at 16:51

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Reply By: Member - Kerry F (WA) - Thursday, Oct 21, 2021 at 20:11

Thursday, Oct 21, 2021 at 20:11
Watch a video on U Tube called Disaster on the canning stock route
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Follow Up By: Member - Mal and Naomi G - Friday, Oct 22, 2021 at 11:45

Friday, Oct 22, 2021 at 11:45
Thanks Kerry F, seen it a number of times already and there's others too. I've got the problem, looking for a solution now.
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Reply By: RMD - Friday, Oct 22, 2021 at 19:33

Friday, Oct 22, 2021 at 19:33
GVM maxing out.
In this thread, and others, the "near GVM" has been mentioned. I would think the manufacturer set the GVM so as to be the maximum sustained load on the vehicle with normal use. Sort of what a tradie may get to for site to site jobs. Then the axle may never fail, they don't seem to fail. If operating at or near GVM and the vehicle has way more stresses applied because of road/terrain then, at MAX GVM is beyond the design. Some regard a GVM upgrade as making the vehicle safer and more capable, it isn't. All it does is probe into the reserve strength/life the maker intended. Sometime it makes them less safe. Eg, Range Rover state a towbar weight ability but if used OFFroad they request the loading be derated at least 1/3.
For the Isuzu standard weight and the GVM weight, perhaps that amount of payload difference has to be considerably cut back so the constant stresses aren't passing the design ability. I can carry 50 kg but not through the bush or fast or over hurdles..
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Follow Up By: Member - Mal and Naomi G - Saturday, Oct 23, 2021 at 11:22

Saturday, Oct 23, 2021 at 11:22
RMD, that's a point we tried to make to Isuzu Australia when we first approached them about our axle housing. The Isuzu DMAX is advertised with the slogan 'Go Your Own Way' which implies that the stated GVM and 3.5t towing capacity applies ANYWHERE you decide to go. But it's been our experience that 'Go Your Own Way' rapidly turns into 'Go Away' when you have a problem with their vehicle!
You're exactly right about GVM upgrades. We were talked into one when we had the suspension first upgraded, but we continued to use the OEM 2950kg GVM rather than the 3300kg engineer-approved limit because we knew only the springs and shock absorbers were upgraded. The axle maximum loadings remained exactly the same and, in the end, it was the axle housing that let us down.
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Follow Up By: axle - Saturday, Oct 23, 2021 at 12:13

Saturday, Oct 23, 2021 at 12:13
G/Day RMD,

I agree 100% on what your saying, and i think a lot of others might do so to after their bank accounts have been lightened somewhat. Whats the use in buying something and trying to make it perform a duty it was never designed for? Marketing Hype and crazy sales dudes are becoming a concern as far as i'm concerned.

Cheers Axle.
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Follow Up By: Member - John - Saturday, Oct 23, 2021 at 12:30

Saturday, Oct 23, 2021 at 12:30
Reply to Mal, I have had a GVM upgrade on my Patrol and part and parcel of that was bracing the rear diff tubes, have no idea how the twin cab utes can have a GVM upgrade with out bracing the rear diff at all. Good luck with Isuzu Australia.
John and Jan

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Follow Up By: RMD - Saturday, Oct 23, 2021 at 13:25

Saturday, Oct 23, 2021 at 13:25
I sort of agree with you and Axle. The advertising isn't inline with the real ability.
As it stands you have been pretty smart in staying with the OE rating and not the "engineer" approved rating, ever seen an engineeer out in the bush? other wise the failure would have been sooner and possibly catastrophic and far worse as some videos show.

Earlier, ie, years ago, I intended to tow my loaded 6x4 trailer along the Oodnadatta track and was told it wouldn't last, it would break. Before setting out I replaced the axle for a square one with falcon outer bearing size. Commodore hubs and UTE strength rims. Fitted landcruiser front springs with less leaves and fitted shocks too. As a result I had long travel, compliant springing and shocks to absorb. Yes there were 7 dead 6x4's on that run along the track, Mine is still working as I made it 32 years ago. No cracks or breaks but tailgate did rust a little. Just the basics, articulation distance with springs, shock absorbers but parts have to be strong enough too, ie, strengthening as John mentioned.
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Follow Up By: Member - Mal and Naomi G - Saturday, Oct 23, 2021 at 14:08

Saturday, Oct 23, 2021 at 14:08
John, RMD,
When you compare the rear axle and diff carrier under the current (2021 +) model and the same components under the 2012-2020 models, you would not reckon they came from the same make and model.
In the comparison the 2012-2020 components seem very underdone. But they are sufficiently strong to carry and tow the rated weights in on-road and mild off-road (farm) conditions.
It is only in extreme conditions that they fail and only a handful of owners every make them work in extreme conditions so the number of failures is not enough to have an impact on vehicle reputation.
Being able to match the competition's claims in carrying and towing capacity seems more important for maintaining or expanding market share than dealing with a problem that only a handful of people will ever experience.
The really annoying part is we have good shocks (remote-reservoir all round so they don't overheat and go away on corrugations) and the suspension didn't bottom out (only once, on the Canning Stock Route, that I can recall) to pass extra load shock onto the axle housing.
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Follow Up By: Member - John - Saturday, Oct 23, 2021 at 14:35

Saturday, Oct 23, 2021 at 14:35
Mal, if the 2021 DMax has had a substantial rear diff upgrade, I would be asking Isuzu why? Maybe because of a few/lot of rear diff tube failures? Is there a DMax forum to ask the question of other 2012-2020 DMax owners?
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Follow Up By: Member - Jim S1 - Saturday, Oct 23, 2021 at 15:02

Saturday, Oct 23, 2021 at 15:02
Cripes John, I thought the Patrol axles and diff were indestructible ...... they're massive !!

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Follow Up By: Member - John - Saturday, Oct 23, 2021 at 15:10

Saturday, Oct 23, 2021 at 15:10
Jim, I have bent a rear one, too much weight will do that. I had my GVM upgrade done by ATOC and as well as new shocks, KONI Raids and new HD springs, the rear top spring mounts and the rear diff are reinforced. Also have the front diff braced, they are known to bend if too enthusiastic. Was not a requirement for upgrade, just belt and braces.
John and Jan

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Follow Up By: RMD - Saturday, Oct 23, 2021 at 16:15

Saturday, Oct 23, 2021 at 16:15
It seems the load and the usage pattern is something which Isuzu didn't test for long enough to reveal the inherent weakness and subsequent flexing causing cracking. I had possession of a V8 Calais vehicle for a while ex GMH, and it had hundreds of stress and temp sensors all over the components to test when hammered on rough roads, Lots of 4wd makers don't seem to go to that degree.
I think you are correct in saying, apart from a few, most won.t experience trouble, but the fact the new ones are BIGGER and indicates Isuzu do KNOW. However for the ones who have a problem there is a strategy used to avert/deflect/refuse any remedial work. They factor into their sales a percentage of failures and use all resources to not fulfill the moral obligation. That is gauged against negative publicity. If the negative reports become too many, it instigates company changes but only if it impacts their name they may decide to try and keep their name. Ask any one in the street and about Dmax axle failures and they won't know. Company banks on that. People who have trouble are simply collateral damage and accepted as normal by the makers. All vehicle companies are the same, same hymn book.
I see Jim's comment for Patrol, my SIL has a cab chassis, which broke and same as John, the spring pads were totally replaced with thick ones. At the beach a couple of years ago a NEW V8 dual cab cruiser broke off the whole swivel housing and wheel as it tried to exit a washaway. Unexpected, but the sudden stresses were simply too great. Hard to drive with only three wheels.
FollowupID: 916781

Follow Up By: Member - Mal and Naomi G - Saturday, Oct 23, 2021 at 17:30

Saturday, Oct 23, 2021 at 17:30
Isuzu well know the problem with 2012-20 axle housings - when I spoke to my local metropolitan Isuzu service centre as first port-of-call in a failed attempt to reach some agreement on price sharing for a replacement housing, the staff said they'd come across the same problem with a MUX (coil sprung rear end but essentially the same housing) - but the problem is numerically small and it's very easy to blame the car owner for overloading.
Isuzu Australia, via the local service centre inspecting and taking pictures, took one look at our DMAX with alli canopy, 80lt water tank under tray, extra D/C battery, fridge, extra spare wheel on back, bull bar (not there's) and bigger tyres (on standard rims), plus the upgrade GVM plate, and automatically assumed we travel overweight (we have the car serviced and checked thoroughly before we go away and the service department is told we are heading to remote outback so fix/change anything that looks even a little suss).
Unfortunately, the last time we had the car loaded up and weighed (2700kg) was several years ago and we've made some changes since then - Isuzu knows no one weighs their vehicle every time they travel, so claiming overweight is an easy out that's effectively impossible to disprove - '10,000 owners don't have the problem, BUT you do, must be something you're doing that's wrong' type argument.
The only consolation is that when you Google 'Diff bracing kits' there are no off-the-shelf kits available to strengthen DMAX back axle housings - the number that do crack is so small no engineering company has bothered putting in the hours to design one - but any number of kits to strengthen Toyota LandCruiser and Nissan Patrol diffs and axle housings, front and back, come up. Obviously Toyota and Nissan have the same problem with cracked or bent housings, but there are enough of those to warrant designing and manufacturing weld-on strengthening gusset kits.
FollowupID: 916783

Follow Up By: RMD - Saturday, Oct 23, 2021 at 18:05

Saturday, Oct 23, 2021 at 18:05
As an apprentice, and during my time in the mechanical trade, Heavy earthmoving/Road making machinery, it was fairly common for professionally designed equipment to crack and break. Mostly we modified and strengthened/braced as required. Sometimes had to make parts with lathe work/welding and or electrical as required. Rarely did suppliers become involved in the wrangle as the machine had to be fixed and out working , NOW. It is hard to take for a private person, when companies don't back you up even when they have full knowledge of the shortcomings but having it rectified by competent folk is probably the easiest. Isuzu won't have anyone employed in OZ who can rectify it and warrant it into the future. Any changes are done overseas in design rooms after feedback, which they have. Some of the assessing people from my experience, lack in ability in many areas they assess. NFI sometimes.
FollowupID: 916785

Follow Up By: Member - Mal and Naomi G - Saturday, Oct 23, 2021 at 19:59

Saturday, Oct 23, 2021 at 19:59
Spot on RMD.
I know from email conversations with Isuzu Australia, there was no one who could tell me the physical differences between the 2012-20 rear axle and diff housing assembly and the 2021+ assembly - other than the current one had an electronic locker which the earlier models didn't have. I may as well have been asking about them about the surface tension of the moon as ask whether the stronger later assembly would fit mine with minimal modification.
FollowupID: 916788

Reply By: Hoyks - Saturday, Oct 23, 2021 at 18:13

Saturday, Oct 23, 2021 at 18:13
Sounds like you're asking more of the D-Max than it was designed for. Might be time to look at more drastic weight loss or trading the D-max in on a NLS, Canter/Fuso, Iveco or something better designed for what you're asking of it.

Snapping a spring, then snapping an axle housing... the engineering gods are trying to tell you something. Beefing up the axle will probably just find the next weakest point, most likely cracking where the chassis kicks up around the front of the leaf spring bush or folding the chassis over the bump stops.
AnswerID: 638371

Follow Up By: Member - Mal and Naomi G - Saturday, Oct 23, 2021 at 20:07

Saturday, Oct 23, 2021 at 20:07
Problem is, they're all physically bigger (as in wider, higher, longer) which can be a real pain on tight tracks. As it is, I really love it when I'm following a 200 Series LandCruiser or big Patrol because I know I'm not going to wear more bush pinstriping.
Think we were unlucky with the spring - as I've said earlier, looks like slag or foreign material in the steel at the break, but certainly weight a factor in cracked housing, no doubt about it.
FollowupID: 916789

Reply By: Rangiephil - Saturday, Oct 30, 2021 at 17:27

Saturday, Oct 30, 2021 at 17:27
I looked at the Canning stock route video and thought at the time, that if only the owner or someone in the group had some welding electrodes and the knowledge to weld, then half of the drama would have been averted.
If the axle could have been extracted and the axle end welded back on then the car could have been towed to civilisation.
Although I note that the D Max has a semi floating axle which would probably mean it needs the diff bearing to align the axle..
Quote from brochure - Rigid semi-floating banjo with hypoid final drive and dual
tapered needle roller bearings. Rating: 1910k unquote
It would be harder than with an older Land Rover which has fully floating axles which allows the car to be driven without an axle. It is cheaper to build semi floating so that is the possible answer.
AnswerID: 638447

Reply By: Member - Mal and Naomi G - Wednesday, Nov 24, 2021 at 23:18

Wednesday, Nov 24, 2021 at 23:18
For everyone who has followed this thread, we have had a new axle housing strengthened which we hope will do the trick.
A 4mm wall thickness tube was plug-welded INSIDE the OE Isuzu pressed rear axle tube, from where the wheel bearing housing is welded on the outer end, to about three quarters of the way in towards the banjo housing, so it well and truly strengthens the housing between the wheel bearing and spring perch (where the previous housing cracked) and continues on under the perch on both sides of the car.
As an extra precaution to hopefully prevent transferring the stress point further along the axle tube, U-section braces were welded under the OE housing from the banjo out along along the axle tube almost to where the bottom U-bolt plate sits, directly under the spring perch on the top half of the axle housing.
This buttress brace is near full depth at the banjo housing and reduces in depth down to the thickness of the extra metal at the outer edge.
We'll try it out on corrugations next year, but it certainly looks the part. Time will tell.
We also plan to change out the +600 springs for +400.
Thank you for your interest and suggestions.
Mal & Naomi Gill

AnswerID: 638700

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