An unexpected mod for the Dmax; a diff drop

A few months ago I didn’t even know that a diff drop was a reasonably common modification done to independent front suspension vehicles. I most certainly didn’t have it planned to go into the Dmax build, and yet somehow it ended up there.

Much like the Dmax GVM upgrade which was never a part of my build plan, things don’t always go to plan, and you have to adapt and make changes along the way. The Dmax diff drop was just a little hurdle to overcome, right before a big trip up north.

EDIT – Here’s the full build; Isuzu Dmax modifications for touring Australia.

If you are keen on knowing how much it cost, have a read of Isuzu Dmax Build Cost.

Why the need for a diff drop?

I’ve never been a fan of big lift kits on 4WD’s, especially on those running independent suspension, as I know how much extra stress it puts on all of the drive line components. However, I never expected to have an issue with this running a mild lift kit.

In essence, a diff drop is fitted to bring your CV angles back as close to flat as possible, which increases their strength, gives you back your suspension drop and reduces their wear.

CV damage on an Isuzu Dmax
The more angle your CV runs on the less travel you have and the easier it is to do damage

OME suspension on the Dmax

If you’ve been following the Dmax build, you’ll know I opted to go for an Old Man Emu suspension package through ARB, which for about $700 extra comes with the engineering and paperwork to certify a GVM upgrade, giving me 270kg of extra available payload.

This kit is supposed to lift the vehicle by 30mm, which was exactly what I wanted, as with the larger tyres I was limited to a maximum increase in vehicle height via the lift of 33mm. The limit in WA is lifting the roof height by 50mm, which this does to a tee. Is your 4WD legal?

I’d done extensive research on the ARB kit, and a heap of comments on various forums suggested that their front springs often weren’t lifting the vehicle up that much. As a result, I asked for their heaviest springs to be put in, which are recommended for vehicles with a fair bit of weight at the front.

Mine has the Bushskinz bash plates, an AFN steel Bull Bar, Runva Winch, N70 cranking battery (quite a bit heavier than the factory one), a catch can, UHF antenna and secondary fuel filter, so well and truly qualifies for the heaviest springs.

I received the vehicle, and took the measurements, and to my surprise was bang on the 28 – 33mm range increase from the factory height, making it as tall as legally possible. In fact, with the LED light bar and big canopy on the rear it is taller than the 80 series I had, and only just fits inside the garage. You need to allow some time to settle, so it will be interesting to see what height it ends up at.

How’s the CV angles?

After driving the Dmax around for some time, a good mate of mine commented on the CV angles; something I’d never really had to look at in the past, due to running solid axle 4WD’s.

I did some research, and compared it to a heap of other vehicles, and eventually concluded the CV angle was too extreme. When you lift the vehicle, your CV’s increase in angle as the distance between your axles and chassis increases.

This effectively reduces the down travel of your suspension by the lifted amount, and makes CV’s extremely easy to break as they have to work very hard at extreme angles. Given the Dmax’s don’t have the best reputation for strong CV’s anyway, it was asking for trouble.

I did some further research, and even read a publication from ARB suggesting they don’t recommend a lift of any more than 25mm due to increased CV angles. This is one of the most common Dmax lift kit problems that people experience. 

The worse CV angles make the CV’s wear out much faster, far more likely to break when off road, and you can have other issues with the front end of your vehicle.

Free wheeling hubs or Diff drop kit

From there I had two options, both of which achieve similar but different things; fit part time hubs so that the CV’s don’t turn all of the time, for about $400, or install a diff drop kit, which would lower the diff back down to near its factory height.

Eventually I went with the latter, and picked up a Roadsafe 50mm Dmax diff drop kit with full ADR compliance Australia wide from Coastal 4×4.

Free wheeling hubs stop your CV’s turning for most of your driving, and make it easier to drive home without opening the tool kit if you break a CV, but they don’t fix the major problem that when you are in 4WD, your CV’s are at nasty angles and are much more likely to break.

80 series AVM hubs
Manual locking hubs or a diff drop, or both?

Fitting the diff drop kit

This was fitted on the driveway in about an hour on the driveway. The fitting is quite simple, although the instructions are not as good as they could be and it suggests using axle stands to hold the diff, which would be important if its only one person doing the job. If you have two, its easy enough to lie on the floor and hold the diff up yourself; its not very heavy.

Are there any Bash plate modifications?

I was told by Bushskinz that one of the bash plates would no longer fit as the diff would touch it, but it still clears by about 15mm. They do sell a different bash plate, as do most underbody protection companies to suit the diff drop kits.

Dmax bash plates by Bushskinz
The Bushskinz Bash plates fit with no issues

How much does the diff actually drop?

One thing I forgot to do, which I was a bit annoyed about, was measure how much the diff actually dropped. Although the spacers are 50mm, because you end up with a triangle between where the spacers are and where the diff is, it actually lowers it less than the 50mm. How much, I don’t actually know, but I’d like to.

Dmax diff drop difference
Drivers side difference after the diff drop was fitted
Dmax Diff Drop photos
Passengers side before and after

The final CV angle is substantially better than what it was, although still not the same as it was from the factory. If you compare a factory Dmax to other dual cab utes, you’ll see that even from factory, their angle is not as good as their competitors, which is obviously going to make them weaker.

I’m extremely careful not to allow excessive wheel spin, not to accelerate hard when turning and especially when the suspension is allowed to drop at its maximum, as this is when it is weakest.

There are a lot of people who have broken CV’s on Dmax’s, and I’ll try as hard as I can not to become a statistic!

Interestingly ARB do not sell or fit the diff drop kits; perhaps they really should.

So, for any Dmax owners, if you are lifting the vehicle by more than 25mm, a diff drop kit is extremely worth while fitting, and if you are going 50mm or more, I’d say its a must, if you want your CV’s to last.

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  1. Hey John,

    Thanks for the comment. I don’t think the diff drop is a must, but its often a good idea. A lot of people don’t run them with two inch lifts, but ARB have pretty clearly said anything over 35mm is worthy of having one.

    Take care

  2. John Kelly says:

    Hi Aron I have a 2013 dual cab dmax that i fitted a 2 inch lift to with heavy duty upgrade to the front and plus 300 for the rear. I am putting a diff drop kit in also as i did a cv already with just normal road driving. Was very concerned when at the 4×4 expo asking about lift kits and the guy from pedders said i didn’t need a drop kit and several other sellers hadn’t even heard of the drop kit so there would be people driving off on there adventures heading for possible trouble. Good article mate happy travels

  3. Ross Rhodes says:

    Hi Aaron
    Thought I’d give you an update on the diff drop.
    Nigel from vehicle safety and standards at D.O.T got back to me on Wednesday. A diff drop in Western Australia is legal now. So long as you make sure to go to the D.O.T website and fill out a Light vehicle minor modification form.
    This can only be done on vehicles that have been raised by a maximum of 50mm at roof height.
    Vehicles with raised roof heights above the 50mm must go in to get engineering approval on height issue ( if not already done ) and for the diff drop to be installed.
    This is due to. The lower you need to drop the diff. The chances of shearing the mountings of the diff drop increase exponentially. ( Nigel asked if knew what that meant )?. I said yep. Diff drops used to be illegal in W.A. Which is why the shop I was at told me that it was. They just hadn’t checked the regulation changes.
    The issue with gvm upgrades comes down to the individual makers of the suspension systems. Pedders Head office said their store that told me it void my gvm upgrade was wrong. It will still be covered. So long as I don’t change any of their parts with another brand. Without getting written authorisation from them first.
    Hope this helps

  4. Hey Ross,

    Some interesting questions. When you start putting multiple aftermarket bits together it is possible its not compliant. As far as I am aware it is still legal, as the diff drop kit is ADR approved, but I could be wrong.

    I’ve never heard of them being illegal in WA, given we go under VSB 14, which most of the country references too. I’ll have to do some digging. All the best

  5. Ross Rhodes says:

    Hi Aaron
    Couple of quick questions.
    Is your gvm upgrade still compliant now you have put on a diff drop kit. As I have been told my Pedders gvm will not be compliant if install one.
    Is the diff drop actually legal in Western Australia as a reputable 4wd work shop said they would not ever install them since they are illegal in Western Australia.

  6. Hi Suresh,

    No, as you aren’t extending the tail shaft. I would however, not recommend you only lift the front as you will ruin the handling of the vehicle. They are designed to point slightly down at the front for a reason


  7. Hi Aaron
    Would the same problem arise if ine is only seeking to level the Dmax with a 2″ spacer up front?

  8. Hey Andrew,

    I would measure the hub to guards and see what lift it actually is, and go from there. You only have to look at a true 30mm + lift and you’ll see the CV angles are not good. A diff drop has caused zero issues for me, and lots of others


  9. Andrew Ronnfeldt says:

    Hi Guys. I have a September 2017 dual cab Dmax with the ironman 300kg plus suspension. I think about 30mm lift in front. Early this year I approached superior (northside of Brisbane) about a diff drop kit and they told me that it would create more binding.

  10. I would start with reducing the weight where possible, and go from there. If you still need to carry a lot of weight then a single cab is most suitable, regardless of brand.

    You can probably do it as originally suggested with a GVM upgrade that also increases the rear axle capacity, and taking it carefully.

    All the best mate

  11. Thank you very much for your experienced opinion. Maybe a Landcruiser Ute with a 500kg gvm upgrade might be the safe way to go?
    Regards, Brian

  12. Hey Brian,

    Being a space cab you are in a better position than a dual cab, but you will still have a huge amount of weight on and behind the rear axle. I would think you’d be well over the factory rating, so unless the GVM upgrade changes the rear axle capacity you may still not be legal.

    At the end of the day drive to the conditions, put all your heavy gear as far forward as you can and it might be OK, but you will need to be very careful with it.


  13. Hello Aaron. I am considering an Isuzu dmax spacecab to put an Active Camper 2.4m on. All up weight carried will be approx 1400kg when fully loaded- Camper 550, alloy tray, larger fuel tank 150l, 200l water, driver & passenger, and everything from front to back of vehicle and food, drinks etc etc. We will need a 350+ kg gvm upgrade and diff drop. Are we straining the Ute with this or would the Cvan angles etc be ok for light to medium 4×4 use? Thank you for your time.
    Regards, Brian Grieve

  14. Hi Matt,

    Is your vehicle a manual? If so, it will be the tail shaft center bearing needing to be spaced down. If it goes away under load then it wouldn’t have anything to do with the CV’s, as your front weight wouldn’t change a huge amount

    All the best

  15. Hey Matt
    I have pedders suspension upgrade but didnt want a lift but just able to carry more stuff without sagging so went with constant 350kg leafs in the rear and slighly heavier than original in the front. I have a slight shudder when taking off, which, after reading your article am putting down to my CV angles, it goes away when i have a load on.

  16. Hey mate,

    I haven’t had any issues with mine yet – the diff drop should return it back to normal height. Did you measure how much the diff actually dropped? Perhaps its more to do with extra flex at the front that allows the CV to drop further than from stock?


  17. Chris Cooper says:

    I have the same issue with my 2015 colorado which has a 2 inch lift. It keeps binding / wearing cv’s so i instaled a superior engineering diff drop but still binds at full droop and chewed out the knuckels. Have you had this problem?

  18. Hey Anthony,

    I think its worth doing. I doubt the standard bash plates would fit with it though


  19. Anthony Whitney says:

    Hi, thanks for the article, you’ve convinced me to put a Diff drop kit in our MUX as part of a 2″ lift (the Roadsafe kit drops by 30mm I think). You mentioned your after market bash plates still bolted back on OK, do you think that would be the case with the standard bash plates as well?

    Thanks, Anthony.