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Cross-axle differential options for Jeep Wrangler JL

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Introduction

In November 2022 Eaton launched their Truetrac differential for the Jeep Wrangler JL and Gladiator JT. This provides a new option to increase the off-road (and on-road) traction performance of current generation Wrangler and Gladiator vehicles.

So here I’ll discuss the various cross-axle differential systems and their characteristics, their relevance to use in the Jeep JL and JT vehicles, and my experiences in installing an Eaton Truetrac in a Wrangler JL Rubicon.

The Jeep Wrangler JL is perhaps one of the most capable off-road vehicles available from the showroom floor, so why would we change either of the cross-axle differentials installed from the factory? In my opinion, the factory installed standard solution using a selectable lockable open rear cross-axle differential is not the right solution for the most driving situations but rather it is only the best option for some extreme off-road situations that occur very infrequently (except in the minds of the Jeep marketing department). This discussion suggests that in almost all traction situations a Torsen cross-axle rear differential will outperform a selectable “locker” open differential.

Differential Types and Mechanics

About 5000 years ago in Mesopotamia the first wheeled Chariots appeared. These vehicles used free wheels attached to the end of a fixed (non-driven) axle. It was only with the invention of the steam-engine and locomotion in the 1820’s that the axle needed to be motor driven and later in automobile applications there was a need to allow the speed of the driven wheels to vary relative to each other, and the cross-axle differential gear was patented in 1827 by Onésiphore Pecqueur.

The cross-axle open differential allows the speed of the two half-axles to vary from 0% to 100%, and it delivers constant torque split to each half-axle. The ratio of the torque split is set by the size of the side gears relative the pinion gears. Usually (always) in automotive applications the side gears are equally sized and this splits the torque exactly half to each half-axle, i.e a 50:50 split of torque. Interestingly, the first use of an automotive cross-axle differential was by an Australian in 1897 in his steam powered car.

It is worthwhile to introduce Newton’s Third Law in terms of torque delivered to an object (half-axle or drive shaft): for every action (torque) there is an equal and opposite reaction (torque). The statement means that in every interaction, there is a pair of torque forces acting on the two interacting objects. The size of the torque on the first object equals the size of the torque on the second object. The direction of the torque on the first object is opposite to the direction of the torque on the second object.

This means that although we often talk about the engine torque delivered through the drive shaft when speaking about a cross-axle differential, what we’re really interested in is the reaction torque generated by traction from the ground to the tire (wheel) attached to the end of the axle. It must be understood that the engine torque delivered to a half-axle will always equal the reaction torque generated by the tire (wheel). If the tire (wheel) has no traction it cannot provide a reactive torque, then the engine will not deliver torque to that half-axle.

Over time the shortcomings of the open differential became obvious when different road surfaces supported unequal wheel torque, such as when one wheel is on ice, mud, or is not in contact with the road at all. In an open differential the maximum torque delivered by the engine will be twice the minimum torque reaction from one of the wheels. Therefore if one wheel is on ice supporting almost no torque reaction, then the engine will only be able to deliver torque as if both wheels were on ice. If one wheel is in the air, then similarly the engine will deliver torque as if both wheels are in the air (i.e. no torque at all).

In the 1960s high power USA “Muscle Cars” started to use limited-slip differentials to prevent the “one tire fire” as their available engine torque would be more than twice the maximum wheel reactive torque which would cause the weakest (lowest torque) tire to break traction reducing friction and its reactive torque capability to almost zero, and as a result the overall torque delivered by the engine would drop to almost zero and the car would sit “smoking” a single wheel. The limited slip differential helped to overcome this problem by using clutch packs or springs to set the minimum torque delivered to each wheel. This means that the torque delivered to each wheel is not able to go to zero, but is set to a minimum value determined by the clutch spring design, however the torque split remains exactly 50:50 as in an open differential.

The limited-slip differential goes a long way to solving the issues encountered by high powered vehicles both on-road and off-road, but it does introduce an additional maintenance as clutch packs in the differential need to be maintained, and they will wear out often if used aggressively.

For off-road and some extreme on-road applications locking differentials have become very popular. When activated, locking differentials effectively return the axle to a solid locomotive axle, and this inverts the torque and speed relationship of the open differential by holding the wheel speed relationship to be constant equal to 1:1 but allowing the torque reaction from each wheel to vary from 0% to 100% depending on what is available. Therefore if a wheel is in the air, it will produce 0% reactive torque forcing 100% reactive torque to be produced by the other wheel, but both wheels will rotate at exactly the same speed. Using a locked differential or “spool” is only useful in extreme situations, and the lock cannot be left engaged. A locked or solid axle will make it very difficult to turn the vehicle, as it will want to travel in a straight line with both inside and outside wheels rotating at the same speed, so it cannot be used in most situations. To overcome the drivability limitations the spool or solid locomotive axle produces both automatic and selectable locking differentials have been produced.

Automatic locking differentials such as the “Detroit Locker”, or the “lunchbox locker”, are constructed with each wheel connected to the drive shaft via a freewheel gear which, when the vehicle is moving in a straight line, will allow the torque to to each wheel to vary from 0% to 100% as in a solid single axle, but will allow a faster moving (outside) wheel to over-rotate freely, while providing torque the slowest moving (inside) wheel. The main disadvantage of this solution is that, when travelling around a corner, drive torque is only available to the inside (slow) wheel while the outside (fast) wheel is freewheeling, but as the inside wheel is the most lightly loaded in cornering it is usually least capable of providing reactive torque.

Selectable locking differentials, such as the Jeep elockers fitted to the Wrangler JL Rubicon, allow the driver to choose whether the differential is in open mode (the usual case) or set to locked mode when needed. The driver is forced to select between the two options, locked torque and open speed (the open differential) or locked speed and open torque (the locked differential), depending on the expected traction. So then the question is when should the differential be locked?

And the answer is: it depends. Essentially, the driver is trying to guess the vehicle traction dynamics, which usually change rapidly. Usually in technical off-road driving the driver will first attempt an obstacle with an open differential, and only when they have failed the obstacle will they will engage the differential lock and try again. A trial and error solution.

Whilst it is possible for the driver to actively select open or locked differentials in low speed technical off-road situations, it is not practical for the driver to undertake this decision every time they face a different real world low traction or differentiated traction situation. In every day situations of low traction, such as accelerating from a country dirt roadside (one wheel on dirt, one wheel on tar), or crossing a curb, or snow or slush on the roadside, ice patches, or any other impossible to predict situation it is certain that the vehicle will be running with an open differential and will therefore face the limits of unbalanced wheel traction.

Ideally the vehicle cross-axle differential would immediately sense which wheel can provide the greatest reaction torque and adjust (or bias) itself to deliver the available engine torque to that wheel without any conscious input from the driver.

In 1958 Vernon Gleasman patented the torque sensing or Torsen differential, which uses the gear separation forces and friction generated by the sun planet worm gear to provide cross-axle torque biasing. The Torque Bias Ratio (TBR) is a measure of how strongly the Torsen differential will lock. The higher the TBR setting, the more aggressive the traction performance locking. Typical TBRs in production Torsen differentials range from 3.5:1 in the Eaton Truetrac, to 2:1 to 6:1 in the Quaife ATB depending on the application for front or rear cross-axle.

The TBR represents the ratio of high traction to low traction that the Torsen differential can allow while remaining locked. When input torque is applied to a helical gear, it creates a series of thrust forces that push that gearing into the differential casing. When these forces push against the wall of the differential casing, that contact creates friction. As the torque load increases so do the forces and so friction increases in proportion to the amount of torque applied. That gives the Torsen differential the ability to support a lot of reactive torque (traction) imbalance when under heavy throttle conditions, yet it still can differentiate freely and smoothly at low engine torque levels, so the car is docile and easy to drive and manoeuvre.

It is worth noting that the HMMVW, perhaps the most iconic modern off-road vehicle, uses two cross-axle Torsen differentials. Although the Torsen differentials provide the best traction for the military cross country application, the fact that the military KISS principle applies and there is no operator input required (unlike a selectable locking differential) and no additional maintenance procedures are needed (unlike a clutch based limited-slip differential) probably also contributes to the US military’s decision to use Torsen differentials in the HMMVW.

Installation for Wrangler JL Rubicon

The new Eaton Truetrac 917A736 for the Wrangler JL and Gladiator JT is specified for all Dana 44 M210 and M220 axles, being for both front and rear cross-axle differentials. This joins the existing availability of the Nitro Helix also available for the Wrangler JL or Gladiator JT.

For reference, the Eaton Truetrac 917A736 is available in Australia from Harrop Engineering, though I used another source to obtain my example.

Leigh Conlan, Aftermarket Sales & Service Coordinator
Harrop Engineering Australia Pty Ltd

It is noted that the Eaton 917A736 is not specified to be compatible with the Rubicon trim level. This is because the Rubicon is already fitted with an electrically selectable locking differential. So by removing the existing differential the engine management system would believe that there is a system fault, and would generate system errors.

However there is a product from Z Automotive called Z locker OEM to resolve this issue. This part is designed to spoof or fool the Rubicon electronics to overcome the fault inherent in the Rubicon selectable locking differential whereby when the locking sensor fails it causes the vehicle electronics to believe that the locker is inactive and therefore register a system fault, preventing the use of both front and rear differential lockers.

The Z locker OEM can be installed to the Rubicon locker wiring, but not connected to the rear differential housing, and the entire axle wiring loom is then zip-tied up out of the way under the vehicle body. The Rubicon electronics believes the rear selectable locker is functioning normally, which also allows the front selectable locker to function normally and the rear selectable locker to be replaced with the Eaton Truetrac differential.

For other Wrangler JL or Gladiator GT trim levels such as Sahara, Night Eagle, or Overland, it is fully supported to install the Eaton Truetrac as normal.

Overall 4WD System

Note that this discussion is relevant to the Wrangler JL rear cross-axle differential only. Whilst Torsen differentials can be used very successfully with high power front wheel drive vehicles and in the front axle of 4WD vehicles, in the specific case of the Wrangler JL Rubicon with an existing selectable locking open differential there are good reasons to retain that capability in the front axle. For other Wrangler JL trim levels should use either a Torsen front cross-axle differential, similar to the HMMWV, or to use a selectable locking differential, similar to the Rubicon.

The Wrangler 4WD system has a locked centre transfer case when used in 4WD Part Time mode which will allow 0% to 100% torque split between front and rear cross-axles, and using a locked front cross-axle differential from 0% up to 100% of the available torque can be directed to either of the front wheels. This allows the entire engine torque to be delivered through one front wheel, should it be able to provide sufficient traction. Several real world tests suggest that if one cross-axle can be locked, then it should be the front axle.

By using a Torsen cross-axle differential in the rear we’re optimising traction in 2WD and 4WD on all differentiated friction on-road and off-road surfaces, whilst adhering to the KISS Principle, so we’re generating the best available traction for most situations (99% of the time). And by retaining the front cross-axle lockable open differential we have the traction option for any remaining extreme situations (one wheel on each axle off the ground).

Testing Results

Check back late June 2023.

Equipment Rack for Wrangler JL

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In Curb Weight I’ve spoken about dividing the weight between the vehicle and an extreme off-road trailer, and how the vehicle was modified to be able to pull the trailer successfully. In this post I’ll cover how I’ve divided the types of load between the vehicle and trailer, and how I’ve built an equipment rack to support the load being carried by the vehicle.

I must mention that a key requirement for the vehicle build was that any overlanding related modifications had to be entirely reversible, and removable. The rear seat needed to be able to be refitted so that the 2 door Rubicon could carry 4 people if needed. So my equipment rack must easily removable too.

Vehicle Contents

I would like the vehicle to be able to leave the trailer at a “base camp” and still have the required equipment to sustain a day (or in an emergency several days) away from the camp site. This dictates what I need to build into the vehicle, and what I can leave in the trailer.

The vehicle must therefore contain the following items.

  • Refrigeration – A 40 litre refrigerator, sufficient to hold frozen or cooled items depending on the length of the passage.
  • Power – 12V and 240V AC systems to power the refrigerator, cooking, communications, and tools.
  • Food Preparation – using 240V AC induction cooking, kettle, and coffee machine.
  • Food – Chilled and dry food sufficient to cover the entire passage.
  • Drinking Water – Potable water either 20 litres or 40 litres depending on the requirements.
  • Clothing – Warm clothing, sufficient to overnight should needs dictate.
  • Communications, and Electronics – Both UHF and satellite communications system for regular and emergency use.

Based on the item lists I’ve prepared the weight of this equipment and stores should be approximately 260kg (including trailer ball weight), and this can be easily carried by the Wrangler JL 2 Door.

Trailer Contents

The Stockman Pod Extreme trailer has a number of well separated spaces, including two drawers and a large tool box, which allow it to safely store lots of smaller items in boxes without too much movement.

The trailer will carry the things that don’t need to go in the vehicle, and either too heavy or too bulky to consider putting in the vehicle.

  • Fuel – In Jerry Cans from 40 litres to 140 litres, depending on the length of the passage.
  • Water – At least 65 litres of possibly non-potable water, carried in the integrated water tank
  • Accommodations – Both a James Baraud Evasion roof top tent, and a Terka tent and stretcher bed, providing options for easy overnight or comfortable base camp builds. Also a 3m x 3m gazebo to provide shade and light rain protection as needed.
  • Furniture – Folding table and camp chairs.
  • Gas Bottles and Food Preparation – Including 2 burner gas stove for food preparation.
  • Large Tools and spare parts – To support repair of moderately major items, and maintenance of the vehicle and trailer.
  • Recovery Equipment – Larger items stored on the trailer, as most recoveries will involve the trailer and necessary items can be moved into the vehicle if needed.
  • Toilet and Hot Water System – To provide hot water for base camp washing and showers, and toilet to provide a bit of camping comfort.
  • Clothing – Additional clothing and linen as required.

Basic Equipment Rack Design

While the design has evolved over the past weeks of the build, it essentially needed to carry 1. refrigeration, 2. electrical systems, 3. water, and 4. stackable food and assorted items. All of this, in a very tight space. Since the Wrangler JL has a swinging tail-gate with a fold down tail-gate table, it made most sense to put the refrigerator on its slide on the left side and the electrical systems in front of it.

On the right side the drinking water would be stored as far forward as possible, and the food and assorted items stored in milk crates which are easily removable and stackable for access. Luckily the width of a Jerry Can is the same width as a milk crate so it was possible to use the same dimension for both.

The Wrangler JL 2 Door has a number of tie down options. There are 4 integrated threaded nuts in the rear of the floor, which can be fitted with high-tensile bolts. But these rear bolt locations don’t control the front of the space effectively. Fortunately there are also strong loops in the forward floor, to mount the rear seat, which can be used to secure the load at the front.

Build Process

This was a custom build, so it was sensible to build in stages so that I could change things if the equipment rack didn’t perform as anticipated. The stages below were each separated by a shake down trip, and the improvements noted through use were incorporated into the following stage.

Stage 1 – Fridge Slide & Jerry Can (Water)

The first stage was securing the fridge and water in a Jerry Can. These two item could then be used to locate and tie down the other items

So this first stage worked well. I’d note that the tilting fridge slide was unnecessary, and a standard (non-tilting) slide would have been smaller, cheaper, and weigh less. I’ve also found that the tilt makes it difficult to store things in the fridge as when tilted things can’t be removed without the stacks of items in the fridge falling over.

I also found that the water in the Jerry Can was unusable, as the full Can is too heavy to remove for use, so it was necessary to use a water pump to deliver the water to the food preparation area at the rear of the vehicle.

Stage 2 – Electrical Panel & Water Pump

The next stage was to securely mount the Renogy DC-DC charger and 2kW inverter into an electrical panel. The electrical panel was built onto the front of the fridge slide, and it helped to substantially strengthen and stabilise the equipment rack.

Noting that the lithium batteries are secured by pressing them between the front seats and the rear foot well. The end of the slide protrudes over the foot well too so the batteries are unable to move, yet they don’t require special mountings.

I attempted to use a Coleman Camp Shower to deliver the drinking water, but the submersible pump was too large to go into any available water grade Jerry Can. The answer was to cannibalise the Coleman Shower, used together with a 6 litre/min 12V pump, which works perfectly. The retention device in the cap has a hole exactly the diameter of the shower hose, so it can be inserted into the top of the Jerry Can with no leaks.

Following the second shake down all of the systems were proven to work as expected, so the final fitting and build could be completed.

Stage 3 – Final Fitting & Milk Crates

At this point the final build was to add hooks to the rack to insert into the seat loops at the front to retain the equipment rack in the event of a roll-over or other eventuality. Although the prior shake down showed that the equipment rack remains stable despite extensive horizontal and vertical shaking and even several airborne excursions.

Locating hooks under rear seat mounts.

The frame is sized to allow two milk crates to be placed one behind another, with 20 litres of water, giving a total capacity of 4 crates below the window line of the vehicle. Where 40 litres of water is required for a passage, it will be necessary to stack 3 crates, which will affect rear visibility but otherwise this is a useful option. As a maximum up to 6 crates could be stacked and restrained in the rear of the vehicle.

Three of four milk crates.
Finished Equipment Rack

The System In Use

The initial usage in two shake down trips shows that the build has been successful. Water, power, and food are all easily reached and used to safely prepare meals.

The trailer has furniture, gas cooker, and hot water systems which will allow longer base-camping to be done comfortably and conveniently, but the above overnight food preparation system is doing what it should.

Wrangler JL Rubicon – Build Log

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As mentioned in Curb Weight I’m planning to use a 2022 Wrangler JL Rubicon 2 Door as my base vehicle. Without going into a lot of detail about its characteristics, it is probably the most capable off-road vehicle available off the showroom floor in Australia. So there isn’t much development required to get it prepared for overland expedition use. In fact many sources suggest that the majority of failure in overland vehicles comes from owner installed after-market options, so to minimise the expense and effort I’ll only be changing what is necessary.

Reverting Australian “Nerfs”

To comply with Australian regulations Jeep have made a few Nerfs to the Australian Rubicon specifications. These include fitting “low-rider” front fenders, and most importantly fitting very small tires (equivalent to those delivered on the Sport and Sahara models). There are a few other shortcuts that need to be remedied too.

Tire Nerf

The Wrangler JL Rubicon was developed to support 35″ tires, and is delivered in the USA with 33″ LT285/70R17 tires. Yet in Australia it is delivered with LT255/75R17 tires. This directly costs 20mm of ground clearance (under the differentials), and affects entry, exit, and break-over angles.

So we’ll specify a new tire closer to the OEM specification, but more appropriate for overlanding, with the following characteristics.

  • Rugged Terrain (All Terrain) tire
  • Light Truck (LT) load specification
  • 3 ply side wall
  • 3PMS Severe Weather Rating
  • 2:1 tire to wheel diameter ratio
  • Not wider than 10″ (255mm) – minimise mud throw – reduce rolling resistance – not attract Police attention
  • Reputable manufacturer

Based on the above specification the best (and only) option is the Mickey Thompson Baja Boss A/T in LT255/85R17. Since the diameter of these tires is around 35 inches it is likely that the OEM suspension on the Rubicon will need extended bump stops to prevent rubbing. Fortunately Teraflex produces a bump-stop extension kit which will reduce the upward travel by just over 1″, which is enough to prevent rubbing.

Steering Damper Nerf

When converting the Wrangler JL to Right Hand Drive Jeep placed the steering damper under the track bar (panhard rod), causing it to be a full 50mm under the lowest point of the suspension. Owners who take their Wranglers off-road always damage the steering damper and can get hooked up on the large attachment point hanging under the front axle.

Australian OEM steering damper location.

The recommendation is to use a Teraflex steering damper relocation kit to move the damper above the drag link and out of the way of harm. Together with the relocation kit it is necessary to add an aftermarket steering damper. The brand doesn’t matter too much but for the record, I used an ORV Rugged Ridge steering damper originally for a JK Wrangler.

Relocated steering damper, with “clubfoot” removed.

After relocating the steering damper, the large mounting point hanging under the axle can be cut off with an angle grinder / cutter. With a fairly neat set of cuts about 2kg of metal comes off the front axle which improves ground clearance and helps with reducing unsprung weight.

Rubicon Lift Caster Reset

The Wrangler JL Rubicon is lifted by over 1″ over its sister models. This provides the space for larger tire sizes, but in doing the lift Jeep did not rework the control arms to retain the designed caster.

Specifically the JL Sport and many other cars use over 6 degrees of caster to stabilise the steering. Caster also has the positive side effect of improving cornering by increasing the steering angle of the tires. However, after the OEM JL Rubicon lift is fitted the resulting caster is only about 4.5 degrees.

Fortunately Mopar produces an extended front lower control arm which is 1/4″ (6mm) longer than the standard length lower control arm. This was produced as part of its Mopar 2″ lift kit. Fitting the extended lower control arm returns the front caster to 5.5 degrees. This quietens the steering and makes the driving experience much more relaxed one one finger steering.

Suspension Improvements

Noted above are the extended front lower control arms and the extended bump stops, so the only additional improvement is the addition of heavy duty shock absorbers (dampers). The majority of protection required will be on corrugated roads, where the suspension travel is minimal and high frequency. This means that external reservoir dampers, which are designed for long travel situations (like a Baha race) are not the best solution. For the Australian outback I have selected to use the Ironman 4×4 Foam Cell Pro dampers. These dampers are traditional double action (not pressurised), with huge oil reserves and very solid (rebuildable) construction. It is also worth noting that they extend the axle droop by over 2″ over the standard dampers, as they are specified for a 2″ lift kit. The extended droop makes the front axle more compliant to the terrain, and more than compensates for the reduction in upward travel through the extended bump stops.

As the ball weight of my trailer combined with the load of equipment will add about 240kg to the rear of the vehicle, it is necessary lift the rear when fully loaded and yet allow the full travel and comfort when the vehicle is used for rock crawling day trips. The ideal solution for this is to use Air Bag suspension assistance, which allows adjustable support up to 400kg. I’ve fitted AirBag Man Heavy Duty airbags and run them at 45 psi to 50 psi when towing and 5 psi when not.

Towing System

The Wrangler Rubicon has a very light weight plastic rear bumper bar. The OEM tow bar is fitted underneath the bumper on a chassis cross member with 4 high tensile steel bolts. The rear recovery hook is bolted to the chassis with 4 high tensile bolts.

To provide a solid towing and recovery platform the rear bumper and hook were removed and a Smittybilt XRC Gen 2 rear bar was fitted. This bar is bolted to the chassis with 12 high tensile steel bolts, 4 in the normal OEM tow bar location, and 4 at each chassis rail. The bar itself weighs over 53kg, and provides a Class 3 Receiver and two recovery and high lift jack points.

Removing the OEM rear bumper necessitates relocating the number plate. The relocation was done with a combination of the included Smittybilt product and an ARB number plate relocation kit.

Trailer wiring for Australian (APAC) vehicles is different to the American (NAFTA) solution. The NAFTA Jeeps do not have a separate brake and indicator system; their brake light is flashed as an indicator. So purchasing a NAFTA Trailer Wiring System is not going to work. The best solution is the purchase the Australian (APAC) Trailer Hitch kit (MOPAR Part Number LA82210162) directly from a dealer. The Australian Trailer Hitch kit includes a 2″ drop tongue, 50mm ball and Australian 7 Pin Flat Trailer Connector, as well as an OEM hitch point (which I have not used).

The international Trailer Brake Controller (MOPAR Part Number 82215652AD) kit works well with the Australian Trailer Hitch kit. The control knob fits nicely into the dash, replacing the 12V cigarette plug, and the ECU can be stuffed up into the space behind the panel in the passenger footwell.

Fitting the Australian Hitch kit meant passing the trailer wiring INSIDE the vehicle (like the Quadratech video) not outside according to the instructions and joining the wiring in the LHS (passenger) footwell with the Trailer Brake Controller.

The accessory wiring and Trailer Brake signal wire are both found in the LHS footwell. From the LHS footwell the power supply for trailer lighting and trailer brake can be (optionally joined to one supply and) passed through the firewall into the LHS front wheel well and so to the battery.

Accessory AUX connection & Trailer Brake Signal Wire

Other Things Worth Mentioning

Added a K&N air box and filter kit, and integrated the OEM cold air intake into the bottom of the K&N air box by cutting off the curved end and cutting a matching hole in the side of the K&N air box. As the K&N filter can be easily cleaned and renewed anywhere, it is ideal for use in dusty outback conditions.

A Taser JL Mini allows the tire size and many other settings to be done at any time. It also provides live info on the manifold vacuum and does light shows when needed.

I’ve added a GME UHF radio in the centre console, connected to a 2.1dB Rubber Ducky antenna on the tail-gate. There is a Teraflex tail-gate mount for both antenna and sand flag.

Also on the tail-gate there is a Rockslide Engineering table, and some additional 12V connectors and USB power supplies powered by the Renogy Lithium 100Ah batteries along with a Renogy 240V 2kW inverter system.

I’ve removed the small 12V Accessory Battery (saving over 5kg), and all associated wiring, leaving just the Auto-Start relay and signal wires in place to ensure there are no ECU codes generated. Bridging N1 and N2 in the power distribution centre ensures that normal service for all power systems is retained, even the Auto-Start function.

ACC battery and associated wiring.

An ARB air compressor is fitted in the engine bay with a RHD specific mount from TLR.

ARB compressor on TLR mount specific to RHD JL/JT.

Sleeping Arrangements

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“There is a time for many words, and there is also a time for sleep.” Homer, The Odyssey.

I think everyone understands the importance of good sleep to physical supremacy, cognitive dominance, and emotional resilience. So, I’m going to examine the options for sleeping arrangements in the Australian bush, and evaluate them based on input from several experts in sleeping in the bush or rough camping.

From the previous discussion on Curb Weights I’ve selected a method to transport sufficient water, fuel, supplies, and equipment to travel in the bush. But, I also need to examine how best to sleep given the impact of common environmental influences in the bush.

Sleeping Options

There are a number of sleeping systems provided by the vehicle and system for going bush. The below images try to indicate these in context.

I’ve found many options are possible. Six major options are indicated above, related to the previous discussion on curb weights, and they are discussed following some basic environmental considerations.

  1. Swag
  2. Tent
  3. Stretcher Bed
  4. Roof Top Tent
  5. Pod Trailer
  6. Teardrop Camper

Environmental Impacts

The environment of Australia plays the major role in determining the best sleeping system. Let’s talk about the environmental aspects of sleeping.

The Wildlife

There are no bears, lions, or other large predatory mammals in Australia. The wildlife is much smaller, more intimate, and loves nothing more than a warm bed to snuggle into during the cold desert nights.

Keeping the local wildlife away out of your bed, and out of your boots, is an important consideration for where your bed should be.

The Dry Creek

When selecting a flat smooth camp site it is easy to believe that a dry creek bed is a good place to spend the night. Unfortunately bush creeks are subject to flash flooding, and the storm which causes the flood may be a great distance away. It may not even rain where you are.

  • the dry sandy riverbed of the todd river near alice springs, NT

While the flood waters will not be as extreme as shown here (Todd River, Alice Springs, Northern Territory), it is very possible that a creek bed campsite can become subject to anything from a trickle of water to an active flowing creek during the night.

The Gibber Plain

The term “gibber plain” is used to describe desert pavement in Australia. It is a desert surface covered with closely packed, interlocking angular or rounded rock fragments of pebble and cobble size. Desert varnish can collect on the exposed surface rocks over time.

Gibber is located across of much of central Australia, and in the desert you’ve a choice of sand dunes, bull dust, or Gibber plains on which to make a camp site. So, remember to take a rake.

Gibber Plain is found in these Deserts

Sleeping Options

Ok, now we’ve got some of the environmental preamble out of the way, let’s look at the options for sleeping comfortably.

Swag

The swag or bed-roll is the traditional method of rough camping in the Australian bush. It is basically a canvas tarpaulin with a mattress inside. They’re quite warm and they’re also waterproof. It zips all the way up so it covers your head, and you have the canvas for a rain cover. The swag is useful for any of the options for carrying the equipment, and can be used in good conditions even when other alternatives are available.

Down on His Luck, painted by Frederick McCubbin in 1889, depicts a melancholic swagman "on the Wallaby".
Down on His Luck, painted by Frederick McCubbin in 1889, depicts a melancholic swagman “on the Wallaby”

The swag is the choice of bedding for a swagman. A swagman was a transient labourer who travelled by foot from farm to farm carrying his belongings in a swag. The term originated in Australia in the 19th century and was later used in New Zealand.

Swagmen were particularly common in Australia during times of economic uncertainty, such as the 1890s and the Great Depression of the 1930s. Many unemployed men travelled the rural areas of Australia on foot, their few meagre possessions rolled up and carried in their swag. Their swag was frequently referred to as “Matilda”, hence the song Waltzing Matilda, based on Banjo Paterson’s poem, refers to walking with their swag. Typically, swagmen would seek work in farms and towns they travelled through, and in many cases the farmers, if no permanent work was available, would provide food and shelter in return for some menial task.

A swag is quite the romantic holiday experience for backpackers, but it is not going to protect the quality of your sleep from gibber plain cobbles, local wildlife, or flash flooding. So its use case is limited to good conditions, and it shouldn’t be relied upon in bad conditions (if you want quality sleep). Score here is 0 from 3 environmental points.

Tent

Tents are the next option to discuss. They can protect you from local wildlife, provided they are always properly closed up and are in good condition. They will protect you from bad weather and some water flow. But inside the ground will still be rocky and uneven if camped on gibber cobbles or other rock formations. So let’s say the tent scores 1.5 from 3 environmental points.

Roof Top Tent

The Roof Top Tent would seem to address all of the failings of a normal tent. Placing the tent up high, with a flat bed and mattress, removes all of the environmental issues and scores maximum 3 points.

However, the RTT has a fatal flaw. Every time you go up to bed, or get out of bed, you have to climb a 2m high ladder. This is not an issue 99 times from 100 times, but if you’re sleeping in it for a year the chances are you’re going to slip at least 3 or 4 times, and one of those times (in compliance with Murphy’s Law), you’ll break your leg, and that fall will occur in the middle of the Simpson Desert.

From that safety issue alone the Roof Top Tent has a complete veto, in my opinion.

Stretcher Bed

The stretcher bed, cot, or camp bed is an option to uplift quality of sleep in a tent, under a swag, or anywhere there is no full mattress available. The stretcher bed adds environmental points to the tent and also to the swag by lifting you above gibber and minor water, and protecting against most of the wildlife issues (except mosquitos).

The Experts agree that if there’s space available they would never go bush without a stretcher bed. The combination of tent and stretcher bed scores the full 3 environmental points.

Pod Trailer

While the trailer, and specifically the pod trailer, is not designed for sleeping, it can be used as an alternative sleeping platform in the case of bad weather, when the gibber or bull dust is too thick to sleep on the ground, or when there is no need to set up a tent.

Pod trailers can be optioned up to become a full soft-floor camper, but that is not the intention of this discussion. The goal is simply to point out that, as an alternative, the bed of a pod or box trailer can be used as a base for a swag or bed roll, instead of using a stretcher bed, and it scores 3 environmental points for this purpose.

Perhaps, the best option is to fit a RTT to the top of a Pod Trailer? This would avoid the fatal safety issue incumbent in vehicle mounting, and score the maximum points.

Teardrop Camper

Sleeping indoors, while in the great outdoors, is the epitome of comfort. Having a clean, dust proof, wildlife proof haven at the end of the day will provide the best possible sleep quality. But, of course this does come at some expense, and the issues covered in the Curb Weight discussion apply. Scores 3 environmental points.

The Experts

My Sister, who went bush for 8 years, travelling in her Falcon XD Wagon between jobs in Ross River, Jabiru, Exmouth and the Pilbara, before completing the Big Lap with her new husband.

My Brother-In-Law, Retired NCO “The Regiment”, 2 tours of Vietnam, and former Instructor at Bindoon Defence Training Area, WA.

Curb Weight

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Going into the Australian Bush requires the intrepid traveller to carry substantial supplies of water and fuel, as well as the normal requirements for living off-grid for extended periods. This is quite different to the norm in international overlanding where fuel and water is usually available in small towns, and is due to the very (incredibly) low population density of the Australian Bush. The population density of the Australia’s Northern Territory is 0.16 people/km2, about 1/100th of the density of Argentina with 17 people/km2, or 1/25th of Botswana with 4 people/km2, for example. So the purpose of my lists is to estimate the weight required to travel with some comfort across long desolate desert tracks, before the required fuel and water supplies are added.

Load Calculation

Whilst my lists remain incomplete they are a useful tool to establish the the total equipment and supplies budget, and then contemplate the best method to carry everything. My current calculation shows that the normal total mass estimate is around of 575kg, including fuel and water. A rough breakdown of the categories is below.

  • Recovery Equipment – 50kg
  • Vehicle Spares / Consumables – 20kg
  • Tools – 30kg
  • Camping Equipment / Tents / Tarps – 90kg
  • Battery & Electrical – 50kg
  • Refrigerator / Slide – 45kg
  • Cooking Utensils – 20kg
  • Computers / IT / Camera – 20kg
  • Clothes / Blankets / Linen – 30kg
  • Food – 30kg
  • Unclassified / Toys – 20kg

Adding to the items above, is necessary to carry water sufficient for 20 days. And fuel to bridge the longer distances between services.

  • Water 100l – 100kg
  • Fuel (incl. Jerry Can) 40l – 50kg

The weight budget must also allow for carrying 60l to 100l of exceptional fuel load to traverse long tracks in the desert where it would be foolish to commence the journey with only 100l (including the vehicle tank of 60l). For some extreme tracks, the recommendation is to start with a minimum total of 200l, allowing for reserves and safety margin.

Now that might look like I’ve budgeted to carry a lot of stuff, but the idea is not to load up to 100% capacity before departure. But rather the calculation is intended to to allow room for growth as over time, as stuff tends to accumulate, and trophies and memorabilia will take up their share of space too. Nobody likes to climb into a vehicle and have their stuff fall out on the road because everything is packed to the roof.

So, I’m going to estimate that a total payload budget of 600kg will be sufficient. How can that payload be effectively carried across sand and rock over thousands of kilometers?

Carrying the Payload

As a starting point, the Jeep Wrangler JL Rubicon 2 door is the chosen vehicle for going bush.

Jeep Wrangler JL Rubicon 2 Door – 2022 – Marketing Image

From the 2020 Wrangler Specification, the Rubicon can carry a maximum payload of 1322lbs, or 600kg, in the 4 door version. The 2 door version has similar mechanical specifications but weighs about 100kg less, but I will assume that it can’t carry a greater payload than the larger 4 door version. Maximum braked towing capacity for the 2 door version is 1497kg. Let’s have a look at some of the options for carrying 600kg with a 2 door Rubicon.

In the above images I’ve considered some alternative solutions for carrying 600kg payload (in green), and the maximum usable axle load (in red) for the vehicle. My alternatives include:

  1. Bare Vehicle – everything inside the vehicle
  2. Roof Rack – 450kg in vehicle, 150kg on roof (and outside)
  3. Roof Top Tent – 500kg in vehicle, 100kg of RTT (and outside)
  4. Box Trailer – 200kg in vehicle, 400kg in trailer
  5. Pod Trailer – 200kg in vehicle, 400kg in trailer
  6. Teardrop Camper – 200kg in vehicle, 400kg in camper

Bare Vehicle

The Wrangler 2 door is a very small vehicle and, although it is probably the most capable 4WD available “off the showroom floor”, loading it up to the maximum payload will make a very uncomfortable origami that would need to be unfolded at each camp and then intricately repacked each morning. Additionally, as the maximum rear axle payload is about 1000lbs, or 450kg, the available payload would be limited to less than the maximum vehicle payload, as there would be no way to share the weight to the front axle.

In my opinion only way to carry 600kg on a Rubicon is to distribute the weight onto both axles by using a Roof Rack.

Roof Rack

By adding a roof rack, and possibly also side racks for fuel and a rear rack for tools and fuel, it is possible to distribute the weight onto both axles, and also increase the load volume of the Rubicon sufficiently to reasonably store the maximum vehicle payload.

The cost for roof rack system consists of a base rack of around A$1,000, guard rails at around A$500, and then vehicle specific mounting kits from around A$400. Accessories to mount shovels, high lift jacks, jerry cans, or gas bottles can be added for around A$200 per item.

Adding a roof rack will increase the loading on the front axle and especially the rear axle up to the maximum design rating of 3100lbs, or 1400kg, and will increase the tire load affecting both sand driving ability and the tire wear characteristics. Axles, wheels, and tires will be running at maximum load constantly. Adding a lift-kit to balance out the spring compression will not resolve this loading issue, and it is likely that the vehicle may end up being over-weight from a legal (insurance) perspective.

Using a roof rack will also significantly impact the dynamics of the vehicle. Adding up to 100kg onto the roof and 50kg to the outside of the vehicle will increase the overall pitch and roll as the track pushes the vehicle around. It will be very uncomfortable, and may actually become unsafe as the maximum approach and departure angles are reached.

On road, which will be the majority of the kilometres travelled, fuel economy can suffer by 10% and up to 25% according to some reports. Where tens of thousands of kilometres are at stake, and fuel is both in limited supply and expensive, it is best not to use a roof rack if there are better alternatives.

Roof Top Tent

The roof top tent suffers from the same dynamics and fuel economy issues as the roof rack, and it is also of very limited application being purely a place to sleep. If a roof top tent is fitted then the top of the vehicle can no longer be used for storing equipment.

A roof top tent costs around A$,5000, but considerably more can be spent if desired.

With the issues associated with roof top tents being the same as with roof racks and offering no other advantages, it is better to seek alternatives.

Box Trailer

Many people have realised the benefits of an additional load carrying axle when travelling around Australia. The typical steel box trailer in the standard 6’x4′ or 7’x5′ single axle configurations lives in most suburban back yards, and has been making the journey to the summer camping holiday since forever. It has become more common recently to add off-road suspension and hitch components to make the box trailer capable of serious expeditions.

The typical suburban box trailer costs around A$1,500, but the vehicle must have a trailer hitch which can cost up to A$2,000 to install, depending on the vehicle. An off-road trailer with uprated suspension and chassis typically starts around A$5,000, but specialist camper trailers can be substantially more. Some fully fitted off-road box trailers cost upwards of A$60,000.

The design and registration of box trailers typically focusses on a gross vehicle mass (GVM) of 750kg and their Tare is typically 250kg, in the best case, leaving a payload capability of 500kg. If our total load can be distributed between vehicle and trailer then we can load the trailer with 400kg, leaving a margin of 20% remaining, and reduce the vehicle load to 200kg.

The load in a trailer is carried with a low centre of mass, so that the dynamics of the tow vehicle are not affected, and having the additional loaded trailer axle reduces the wear on the vehicle axles, wheels and tires.

However, towing a box trailer does not come for free. There is an increase in fuel consumption to be expected from towing. Depending on the size of the load carried and the amount of wind drag created by the trailer, the increase in fuel consumption may be up to 10%. This is significant, but it is much less than if a similar load were on a roof rack. And, as we now have a greater free load capacity it is possible to carry up to 100l of extra fuel as needed.

An important advantage to using a trailer is that it can be disconnected from the vehicle and left behind at a camp site, or trail head, when its contents are not needed. Through this method most of the payload associated with living does not need to accompany the vehicle on a difficult 4WD trail. This minimises the chances of breakage or damage to the payload.

The box trailer has several disadvantages. Firstly, the load is carried open and unsecured, and secondly, the payload is subject to dust and sand from both the vehicle rear wheels and the environment generally. Whilst Australia is generally safe, for piece of mind, it is best to keep valuables and equipment hidden out of sight when the trailer is left behind. So box trailer loads are usually covered by a tarpaulin or load cover. This adds to the soft security of the load, and helps to prevent dust and sand ingress, but it is time consuming to wrap and tie down the load each morning.

There are many advantages to using a simple box trailer to carry the payload, but it would be more ideal if the box trailer load could be covered by a solid lockable lid to secure the load and mitigate dust and dirt ingress.

Pod Trailer

Recently advances in plastics technology have enabled the creation of large roto-molded polyethylene structures, and companies have started to produce off-road “pod” trailers using polyethylene tubs and lids jointed like a clam shell and sealed with a gasket to produce an effective dust seal.

Typically these pod trailers incorporate all of the advantages of the box trailer, adding in the tare weight saving of a dust resistant plastic tub and sealed lid, and the aerodynamic efficiency of a smooth load top.

Many pod trailers can carry a payload of 750kg to 810kg, with their GVM being 1250kg with trailer brakes. An extreme off-road pod trailer can cost from A$13,000, and customisation and options can be added to increase the suitability for long distance expeditions.

With an appropriate off-road independent suspension, hitch, and trailer brakes, a pod trailer can follow behind a vehicle on all but the most difficult 4WD tracks. And where necessary the secure lockable pod can be left behind at a camp site or trail head.

Teardrop Camper

Moving up from the box trailer or pod trailer solution, it is possible to consider a teardrop or square drop camper. The key advantage of the camper is that the question of sleeping arrangements is answered by a permanently made bed. At the end of a day, or when weather is bad there is a lot to be said for a ready-made bed.

A teardrop camper is usually a significant Tare approaching 900kg, and they can usually carry at least 400kg and up to 800kg in payload. They can easily accommodate the 400kg we need to carry. However the camper GVM will certainly be approaching 1,900kg when fully loaded. This is about 1 Tonne more than a box or pod trailer.

Teardrop campers range in price from A$50,000 and up to around A$100,000, making them potentially more expensive than the tow vehicle.

Besides the large GVM of the teardrop camper, there is a cost to transport the volume for a bed and “sleeping space” around the country. The cost comes in increased the form of increased drag and increased fuel consumption from the larger box, and in reduced space to store camping equipment, unless the potentially dirty equipment is transported on top of the clean made bed.

Conclusion and Decision

Following on from the discussion above, I have decided to go with the pod trailer solution. Although using a trailer will close off some of the more extreme trails and options, such as parts of the CSR, the flexibility to leave the pod and equipment safely behind at the campsite, and have the small tow vehicle remain relatively unmodified (no heavy duty springs, or body lifts, etc), together with the other points discussed above, make the pod trailer the best value for money.

The pod trailer has some further advantages that I’ll discuss in a post on Sleeping Arrangements, and also further in my Stockman Pod Extreme delivery notes.

On Lists

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Really, I should be doing better than this. With a background in Agile Methodologies and Waterfall Project Management, using lists is positively Neanderthal in comparison. Yet, here I am. To get things done, and to remember what needs to be planned and done , I’m writing lists.

About a month ago I asked a good friend whether he’d be interested to join me in the bush for a while, since it had become obvious the only other interested co-traveller was our family dog. His response was, “Would I like to have a copy of a mutual friend’s 23 camping lists?” To which I just laughed. I mean 23 lists… come on. How many lists to you need to leave the house for a few weeks?

A list

I didn’t think about lists for a while. But then after consuming another 20 hours of YouTube suggestions and recommendations for overlanding or international expeditions, I could no longer hold all of the thoughts and ideas in my head. And then I realised that this mutual friend has the right idea. Put it on a list and then it is managed. Putting it on a list doesn’t get it done, but it does get it reviewed every time the list is examined.

One month into this, I’ve established 11 lists for going bush. At this stage I’ve written no lists of destinations or activities, but rather focussed entirely on what I’ll need to make sure that being out bush won’t be life threating, and will be mainly enjoyable.

So here’s my “TOP 11” List of Lists for going bush.

  • Vehicle – accessories and upgrades
  • Recovery – how to recover from vehicular stupidity
  • Tools – fixing things that fail
  • Spares – consumable items for vehicles
  • Camp Equipment – portable lifestyle
  • Cooking Utensils – to eat healthily
  • Camp Consumables- not quite food, but related
  • IT / Photography – toys related to bush activities
  • First Aid – fixing human / canine damage
  • Clothes / Linen – staying warm, and staying cool
  • Paperwork – licences, registrations, insurances, certificates

There we are. 11 lists to manage. I’m sure that by the time I’ve gone bush there’ll be a few more to join these.