4x4

Diff Drop Options on a 4×4 with independent front suspension

Those wanting to challenge their 4×4 offroad will need to lift it but independent front suspension presents a challenge.

ONE OF THE FIRST things most people do after purchasing a new 4×4 is to fit a lift/suspension kit.   Whether it’s for looks, additional ride height, clearance for larger tyres or all the above, it’s important to understand your suspension system on your vehicle and how it all works together to provide you the on road comfort, the off road performance, and the reliability on driveline components. The latter is what we will be focussing on here, particularly the aspect of diff drops in relation to Independent Front Suspension (IFS) equipped vehicles, such as the late-model Hilux.

1 – Background

The reason for considering a diff drop in the first place is to minimise the CV shaft angle that is increased by the addition of a suspension lift. As the suspension is raised higher, the coil overs/struts push the lower control arms further down, thus the hub is now in a lower position relative to the front diff housing which remains static and in its fixed position on the vehicle cross member.   This increases the operating angle of the front CV shaft assembly, which can:

a. Increase wear on the CV joint prematurely;

b. Increase wear on the rubber CV boot ribs prematurely;

c. Weaken the joint since its operating closer to its maximum angle than it previously was; and

d. Increase the chance of the CV shaft pulling out of the inner joint.

Basically, you risk causing a CV joint failure which if you’re not handy on the tools, will mean a tow truck ride back home and to the mechanics for costly repairs or considerable time off-road whilst you repair the vehicle to a “driveable” state.

Not all vehicles/vehicle setups require a diff drop. The general rule to follow is that anything over a 2” suspension lift over stock should consider a diff drop, and those with lifts below this can get away with it. That is not to say that in some applications, a diff drop would not be an improvement on your setup even if sitting at only 2” of lift.  If you’re running long travel coil overs and aftermarket upper control arms and wish to take advantage of a little extra open suspension travel without pushing the CV shaft past its limit in the stock position,  then a diff drop would allow you to gain a little more travel until the point the CV will bind. Which is when you know that you have maxed out your suspension travel and should adjust it back a little.

Every setup is designed to what the customer is after, and we will explore the various options on the market and how they operate below, for you to make your own educated assessment.

2 – Non-Diff Dropped Brace

This is a relatively new product to the market and although it doesn’t drop your diff, it is there for customers that wish to strengthen their non-diff dropped setup, typically around the 2” lift mark, where the drop isn’t required but the upgrade in strengthening is. Why is an upgrade in strength required?

Hilux’s standard cast iron diff brackets have had cases in the past where in low range, in the wrong conditions, typically in reverse, the additional torque through the transfer case has caused the driver’s side diff bracket to bend.   The result of this is that the driver side of the differential tube now sits slightly higher and the previously safe amount of suspension droop you already had, has now pushed the cv shaft joint past its safe operating angle, resulting in either the inner shaft popping out of the inner joint which can cause additional damage when the suspension immediately compresses afterwards with the loose shaft not going back into the inner joint as it should,  or the outer joint binding and breaking with resulting driveline failure.

The Brace, is a stronger metal driver’s side bracket replacement that ties the front differential between the front engine cross member and the rear engine cross member via heavy duty bushes. Tying this from front to rear greatly minimises the twisting/torque forces applied to the driveline and providing security and strength overall.

3 – 1″ Spacer Diff Drop

This design has been around for a long time now, as long as independent front ends have been used. They are a cheap cost effective method to reprieve your CV shaft angle. They are marketed as a “1 inch diff drop”, and this is true, to an extent, but they do not in real world conditions provide the cv shaft angle reprieve that is advertised.  Let me explain:

The 1” Spacer Diff Drop, work by fitting 1” spacers at the front diff mounts where they connect to the front engine cross member. They are fitted in between the front standard diff mount arm and the underside of the cross member. This is where the 1” drop is actually measured from.

The problem with this type of setup, is that since they are only spacing the front diff brackets lower, they are not doing anything about the 3rd rearmost diff mount, which remains static in its original position.  When measuring the 1” dropped front mount, respective to the fixed rear mount, and considering the location of the CV shaft itself in between both, which we are trying to help reprieve operating angle, remember?   We find that we barely get 0.5 of an inch drop at the point where we are looking for it the most.  The diagram below explains what I am saying perfectly:

Consider also that you have lowered your front end an inch, which might require modifications to your bash plate, which is also located in the important area of your vehicle where approach angle is everything, thus possibly impacting on this as well.

4 – Differential Relocation Brackets

These are the newer styled “diff drops” that actually provide additional “drop” and effective cv shaft angle reprieve as intended.   These provide close to 30mm of “level” cv angle reprieve.  This is achieved by replacing all three factory diff mounts for newer ones that are stronger, with heavy duty bushes in the front mounts, and utilising the standard bush into the new rear mount. When all fitted, a lower level is achieved.

With these diff brackets, due to the new lower position of the front diff, the bottom of the diff “hump” protrudes past the bottom of the engine cross members,  requiring the installation  with these kits of a new bash plates that takes this into account and is sufficiently strong enough to protect the diff itself

This hump is not a major issue when offroading as its location is in line with the CV shaft and tyres, so whenever the tyres begin to climb up and over something, the diff this hump lift up accordingly. It’s a negligible loss of clearance for the benefits it provides.

5 – Braced Differential Relocation Brackets

These are an even newer design that has come out in past 12 months or so, that takes the strengthening of the overall design up an extra level. Just as explained with the Non-Diff Dropped Brace,  these kits tie the front engine cross member to the rear engine cross member with a thicker and stronger drivers side mount as part of the diff drop/relocation bracket assembly.

These newer diff relocation brackets can achieve up to 35mm of “level” diff drop of the CV shaft angle, thus helping as mentioned, to maintain reliability with a lifted application, and/or to take advantage of additional open travel with a long travel coilover setup.

Note:  Comparison above from the same point of reference shows a full 34mm drop afterwards.

These braced diff relocation brackets also still work with the bash plates that accommodate the diff drop mentioned in the previous point.

Conclusion

So whether you need a strength upgrade in a non diff dropped application, a diff drop to maintain driveline reliability, or you’re pushing the boundaries off road and require as much open travel as your setup can muster, there is a product to suit your requirements. I would highly recommend that a qualified and experienced 4×4 mechanic attempt any work on your vehicle, as some of these setups can be a little fiddly to install especially if working on them at home on the floor of your garage.


Subscribe
Notify of
guest
0 Comments
Inline Feedbacks
View all comments
maxf

maxf

Max has 21 years of experience with Toyota Motor Corporation Australia. A Toyota qualified Automotive Technician, now working as Technical Officer in the Parts & Accessories Risk Engineering Group.

Also owner and operator of Hillside Offroad and a huge Hilux enthusiast.