Info on DMAX back axle housings

Submitted: Tuesday, Jun 29, 2021 at 22:06
ThreadID: 142062 Views:9251 Replies:8 FollowUps:11
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Hello DMAX/MUX owners, can anyone put us in touch with a differential specialist who can answer some questions about Isuzu rear axle housings.
We want to know what specific physical differences there are between the 1680kg gross rated rear axle housing under our MY2015 DMAX 4x4 crew cab and the 1870kg rated housing used under MY2017-20 models, which have the same rear track and same 2950kg GVM as ours?
Is the axle tube O/D the same on both housings? What would we have to change to fit the later, heavier rear axle housing to our car?
We understand there may be two extra bolts holding the later diff carrier on the front of the heavier banjo housing. If we bought a later banjo housing and diff carrier, could our diff centre, pinion, bearings etc be transferred to the later assembly?
Or, would trying to find an apparently gold-plated priced and rocking-horse-poo rare MY2017-20 complete rear axle assembly at a wreckers, have it reconditioned, checked for straightness and fitted to our car, be the more practical and ultimately less expensive way to go to strengthen the rear end?
Alternatively, if Isuzu Australia decides it will replace our cracked housing under warranty (78,500 kilometres, a lot of them loaded up to 2700kg on Len Beadell tracks and corrugated outback roads, but sensibly driven, higher sidewall tyres on standard steel rims down to 28psi to absorb some shock and with upgraded heavy-duty springs and remote-reservoir shock absorbers), what options are there for strengthening the lighter 1680kg-rated housing?
Really happy with the DMAX, just disappointed in the too light OE rear axle housing that has cracked from the outside weld on the spring saddles on both sides - bit of a shock to see diff oil running down the rear outside U-bolt thread and forming a puddle on the ground when you’re still 130ks from help!
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Reply By: Member - John - Wednesday, Jun 30, 2021 at 06:46

Wednesday, Jun 30, 2021 at 06:46
Good luck, maybe try FB for DMAX groups?
John and Jan

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AnswerID: 636986

Follow Up By: Kazza055 - Wednesday, Jun 30, 2021 at 09:42

Wednesday, Jun 30, 2021 at 09:42
Better still have a look at these 2 Isuzu Forums -

Lots of info there and many well informed members.
FollowupID: 914942

Reply By: Jackolux - Wednesday, Jun 30, 2021 at 07:47

Wednesday, Jun 30, 2021 at 07:47
If you have cracked the rear axle housing , you had better have a good look under the bonnet at the inner guards for cracks there as well .
AnswerID: 636988

Reply By: RMD - Wednesday, Jun 30, 2021 at 09:49

Wednesday, Jun 30, 2021 at 09:49
It appears you ae well informed with the cracking issue of the diff axle tubes. EO member IDLER Chris has just gone through the crack issue and replaced his rear axle. He may know if the bolt pattern is different and your diff carrier would fit into the later model banjo housing. Perhaps contact him through the member system and ask. I had a some communication with him to discuss the issue. He has completed his by now so maybe able to give very accurate advice.

Personally I would remove the axle housing, remove axles, and then have the half tubes added/welded to the bottom of the tubes and webbing welded to the upper outer portions. Both these reaching to the bearing area. Upgraded heavy duty springs which are more than you require may be adding to the stressing of the rear axle and have reduced compliance of the suspension action. While shock absorbers have to be capable of controlling the load, to stiff and not compliant also adds to the axle stresses. A balance is needed there for sure.

Where they crack ,( ie, 60 degrees at rear of the axle tube) indicates the axle material is being compressed at that weld region and flexing. Yes, a bit light for that level of duty.
AnswerID: 636990

Follow Up By: Member - Mal and Naomi G - Wednesday, Jun 30, 2021 at 11:18

Wednesday, Jun 30, 2021 at 11:18
Thanks for the info RMD. I'll try and contact IDLER Chris. We asked our local Isuzu service manager to investigate whether the 'lighter' and 'heavier' banjo housings were interchangeable. He said he asked Isuzu Aust and was told they were not, but that might just be because the 'light' banjo housing and the 'heavy' diff carrier have different bolt holes.
We have +600 Old Man Emu leaf springs and Dobinson shockers (we had a problem with a Dobinson spring 2 years ago and changed them out, it was a fault in the steel, you can see the colour difference of contamination in the metal where the spring eye snapped) but the suspension is compliant and comfortable, even when not loaded up - given that we have an alli tradie type body, second battery, tyre pump, first aid kit, fridge (37lt from memory) and fridge slide, extra steel spare wheel and two camp chairs on the back and a plastic water tank with up to 80lts in it under the alli tray, pretty much all of the time.
We had the leaking passenger side of the axle housing welded up in Geraldton to get us home to Perth. The engineering business welded up the crack and welded a strip of steel about 1/3 the circumference of the tube to the outer edge of the spring saddle and along the top of the axle tube out towards the bearing housing to stiffen the housing.
The U-bolt plate under the axle housing is shaped to the diameter of the axle tube which makes welding anything to the bottom of the tube to strengthen the critical flex area immediately outside of the plate problematic because it changes the O/D of the axle tube and the depression in the U-bolt plate is no longer a perfect fit.
On the passenger side, the crack started alongside the front edge of the outer spring saddle weld and travelled backwards around between half and 2/3rds of the tube, only the front was still holding on. On the driver's side a small crack travelling rearwards from the back of the outer spring saddle weld appears to have formed, but I haven't had a real good look at it, just enough to confirm that side's also cracked.
Cheers, Mal
FollowupID: 914946

Follow Up By: RMD - Wednesday, Jun 30, 2021 at 12:52

Wednesday, Jun 30, 2021 at 12:52
I often do things other don't do or don't seem to do. I find drive line angles as well this way with a digital angle gauge. Handy if raising and keeping driveline angles correct.
Lie down under an Isuzu at a dealership and take a measuring device and count the stud pattern on a new model + photograph it, and see if yours is the same or what differences may be in pitch circle dia or pattern and stud numbers or stud dia. If you do, you will know far more than ANY dealer in OZ will possibly know and probably most in IUA where most have never touched one or had reason to check differences. You will then be the most informed in OZ!

Having a half circle tube underneath, maybe400mm t0 450mm long will add strength to underside. I am not a fan of what you described having been done in the repair, ok in emergency but not long term. At top , a tapered but wide plate which is curved to axle tube at outer end, and welded in place from bearing housing to spring pad will vastly reduce the tube flex which is causing the cracks. I agree the lower plate would need modification to allow secure fastening of the ubolts. Any metal worker worth their wage should be able to make a very suitable plate for each side.

If the tube had cracked to the extent you describe you are very fortunate to have it repaired at that time.

It is strange IUA testing in OZ has not revealed the inherent weakness when travelling in outback. Their ads indicate a GO ANYWHERE capability. If you talk to Chris via messaging he can contact me and further discussion can be done via phone if required.

Hope all goes well.
FollowupID: 914951

Follow Up By: Member - Mal and Naomi G - Wednesday, Jun 30, 2021 at 15:26

Wednesday, Jun 30, 2021 at 15:26
RMD, you've got my Sunday morning planned out for me.
Had decided to go to the local dealer's yard and slide under one this Sunday (when I won' be pestered by salesman trying to sell me a new DMAX, but I might have the local police stop and ask what I'm doing). We first noticed oil spots on chassis rail while pumping tyres back to road pressures at Newman (had done GCR from Laverton, Sandy Blight Junction Rd, Kintore Rd, Haasts Bluff Rd into Alice Springs, then Kintore Rd, Garry Junction Rd, WapetRd/Jenkins Track/Nyangumarta Hwy, Telfer Mine Rd to Marble Bar) but thought it was from the catch can drain hose leaking. More oil spots by Cue but nothing particularly on back axle and still assumed was catch can dripping. Stopped 70ks west of Yalgoo on Marble Bar Rd to Geraldton to check and found oil oozing from under the U-bolt plate and running down the U-bolt. Quickly jacked p/side of car up to save diff oil, dropped U-bolt plate, cleaned axle housing and plastered metal putty over crack to hopefully keep oil in, replaced U-bolt plate and drove 130ks into Gero at 60kph watching the l/h mirror for a wheel wobble. The welding at Gero was done on the basis it was temporary to get us home and there was no guarantee the real wheels would be parallel or vertical. From the squarks coming from the rear end - which hadn't been there before - I'd suggest the rear wheels are now neither parallel or vertical. I'm hoping to track down a Perth engineering firm that has experience with strengthening DMAX axle housings.
FollowupID: 914956

Follow Up By: RMD - Wednesday, Jun 30, 2021 at 16:50

Wednesday, Jun 30, 2021 at 16:50
It is good you realize the wheels may not be operating in a parallel plane anymore. Hard to correct it if trying to reuse OE axle housing. As an apprentice I had to do such checking to be qualified and it is careful work and setups involved. Might be best to have both axles carefully looked at and spun between lathe centres to ensure all is revolving with no bends induced by the housing cracks. Most axles don't tolerate off line driving and they can become stress cracked near bearing area if that section is not concentric with the housing, ie, bearing bore not aimed at diff side bearing bores.

In the event you have to use the OE axle housing, it may be possible to have someone machine some suitably sized steam pipe so it is a press/hammer or heat and cool fit inside each side of the cracked area after each side is cut off the axle housing and the steam pipe plug welded inboard and outboard of the spring pads. You may have to remove some of the axle tube seam internal weld if it protrudes inside where the "New Tube" wants to go. Have to ensure ID clearance for the rotating axle though. That way, there is a fair chance the bearing and diff alignment and wheel plane parallel's would be close if not quite ok. This is all what I can think of at the moment.
I was under a local dealers Ford ranger, checking angles and mountings for members raising their vehicles while retaining drive angles and having no shudder. etc, and sales staff wondered why, and after a chat they just see me as crazy, I am ok with that.
FollowupID: 914957

Reply By: Phil B (WA) - Thursday, Jul 01, 2021 at 10:05

Thursday, Jul 01, 2021 at 10:05
Sorry to be the bearer of bad news - check this article out.

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AnswerID: 637010

Follow Up By: Member - Mal and Naomi G - Thursday, Jul 01, 2021 at 10:27

Thursday, Jul 01, 2021 at 10:27
Thanks Phill B. Aware of that one, and others. Hoping to find a solution.
FollowupID: 914966

Follow Up By: axle - Thursday, Jul 01, 2021 at 12:59

Thursday, Jul 01, 2021 at 12:59
G/ Day Mal.

What a pain!...Have had the same agony with trucks with light housings, and cracking. What we did learn was no matter how good a job was done with welding etc, unless the load was reduced dramatically the same thing will eventually happen again. if wanting to carry the same weights , maybe a different vehicle ,or upgrade to the heavier housing, because the cost of repairs will make you sick! , As the CSR episode has demonstrated. Hope all works out.

Cheers Axle .(...LOL.)

FollowupID: 914968

Reply By: RMD - Thursday, Jul 01, 2021 at 14:16

Thursday, Jul 01, 2021 at 14:16

Just out of interest, did you use airbags to cater for additional weight and ride height? I see the article Dmax has airbags and others which have cracked also used airbags. Perhaps not all cracked axles have airbags fitted though, as the failure can occur under certain conditions.
The reason for asking is, although the airbag makers claim a bump stop is internal there isn't much room for a bump stop in the height of the bag and it's bracketry/ fitment vastly reduces the upward movement of suspension and introduces "suddenness" into the axles upward movement which has to be causing high/extreme stresses.
I used some, still have them, on a 61 series landcruiser and was acutely aware of any bottoming. The shock felt was far far worse than the OE bump stops ever did under same conditions.
AnswerID: 637012

Follow Up By: Member - Mal and Naomi G - Thursday, Jul 01, 2021 at 23:45

Thursday, Jul 01, 2021 at 23:45
No airbags. Loaded, the car sits flat with plenty of distance between bump stop and chassis rail and no signs of scuffing on either the bump stops or underside of chassis rails to indicate maximum spring deflection under load.
In five years of outback touring, I can only recall two occasions where the rear suspension has bottomed - on sand dunes going in to see the plane wreck off Anne Beadell Hwy in 2018 and coming off a sand dune on the joint 60klm section of the Canning Stock Route/Talawana Track and dropping into a hole somebody going the other way had dug at the bottom of the dune in 2019.
There were no severe hits to the rear end in our latest trip.
My gut feeling is that the cracks are the result of axle housing flex over an extended period - 70,000 or more kilometres - NOT necessarily started by a one-off suspension crunch, just plain metal fatigue. That might explain why they didn't show up in initial Isuzu testing - the testing might have been rigorous enough, but not long enough in duration to present the problem.
In this forum in 2019, another member reported cracks outside of the outer welds on the spring pads on both sides of his DMAX, the same model year as ours with similar kilometres and similar outback touring usage - in his case, all of the Len Beadell tracks and the Gibb River Rd, where the cracks first showed up.
His and our cracks both showed up after extended travel heavily loaded, but NOT overloaded, on corrugations, not necessarily particularly bad corrugations, just constant.
FollowupID: 914980

Follow Up By: RMD - Friday, Jul 02, 2021 at 09:23

Friday, Jul 02, 2021 at 09:23
Thanks Mal.
I was just checking about any airbags seeing others had used them. I agree it is the flex and repetitive flexing which seems to cause the failure.
FollowupID: 914982

Reply By: Phil B (WA) - Friday, Jul 02, 2021 at 04:35

Friday, Jul 02, 2021 at 04:35
Hi Mal

Another one has been brought to my attention.

" ... rescued this May 2021 on Great Central Road, a 2015 Dmax with 73,000 km and a standard suspension. That’s two with snapped banjo's and now three with right hand rear wheel problems."
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AnswerID: 637028

Follow Up By: Member - Mal and Naomi G - Friday, Jul 02, 2021 at 08:48

Friday, Jul 02, 2021 at 08:48
That's an interesting one Phill B because it's cracked at the inner end on the axle tube. Mine and others I have heard of generally cracked at the outer end of the axle tube, between the spring pad and wheel bearing boss, with the cracks appearing to start in the vicinity of the outer weld where the spring plate was welded to the axle tube during manufacture.
FollowupID: 914981

Reply By: Idler Chris - Friday, Jul 02, 2021 at 14:41

Friday, Jul 02, 2021 at 14:41
As mentioned by RMD I have had this issue and have a solution. I am happy to talk with anyone about it just let me know. My email address is in my profile but if it is any easier you can ring me 0419846292. I am currently in Quilpie and travelling as usual. Probably won't be home till around November. Leave a number and I will ring when I can. Chris
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AnswerID: 637034

Follow Up By: Member - Mal and Naomi G - Friday, Jul 02, 2021 at 15:17

Friday, Jul 02, 2021 at 15:17
Thanks Idler Chris, I'll be in touch. Interested in your solution.
Cheers, Mal
FollowupID: 914999

Reply By: swampy - Sunday, Jul 25, 2021 at 20:14

Sunday, Jul 25, 2021 at 20:14
Best solution is a custom housing , [sheet metal centre] [shoulder gussets ] [ internal gussets ], thick wall tubes, horizontal axle tube brace . about 3000$
AnswerID: 637291

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