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Does your towing auto box need one of these.


Any 4WD modification needs to be carefully assessed and then implemented with caution. As with many well-meant initiatives, there can be unintended consequences.


First up, it needs to be understood that any change to the original equipment maker’s (OEM’s) specification has consequences – some of them unforeseen. (Leonardo da Vinci, back in the 15th century, knew that: ‘everything is connected to everything else’.)



For example, a change to larger diameter tyres is done ostensibly to increase ground clearance. However, it’s our experience that, in the majority of real-world cases, it’s done because it looks ‘muscular’.

“OK, so what?” I hear you say. “A bloke’s or sheila’s fourby has to look the part and what harm can it do?”

Well, potentially, it can do a great deal of harm. Any increase in rolling radius seriously affects braking performance, because the braking power of pad on disc now has to work through that longer radius. Braking power will certainly be diminished and stopping distances will be greater.

A larger diameter tyre also affects the final drive – differential ratio – gearing of a powertrain that was designed for a specific maximum rolling radius. The final drive gearing effectively becomes ‘taller’, reducing lift-off torque and sometimes making overdrive top gear so ‘tall’ that the 4WD won’t ‘hang on’ as well in top gear on grades.

That confuses the automatic transmission shift protocol installed by the OEM and can see the box ‘hunting’ in and out of torque converter lock up, or up and down ratios. That, in turn, sends the transmission fluid temperature up.



Let’s look at another common modification: a ‘chip’ or engine ‘remap’, to increase power and torque. 

There’s no doubt that OEM engine fuel map settings are conservative, to ensure that today’s already very highly stressed turbo-diesels can make it through the warranty period without disaster. 

There’s also no doubt that more power and torque can be produced by a change to the OEM parameters, but no matter what the retune salesman tells you, that’s done by increasing the amount of fuel that’s injected into the cylinders.

Now, the same vehicle will fairly rip up hills it struggled on before and the transmission temperature usually won’t go up much. However, an exhaust gas temperature probe will almost certainly show a huge increase in exhaust gas readings and the coolant gauge is also likely to climb. Engine longevity is certainly compromised.

These increased engine outputs also confuse the auto transmission shift protocols, because the peak torque and maximum power points in the rev range have shifted.  Also, the light-accelerator power and torque curves look different and the transmission ECU gets confused about what it should do with ratio selection and torque converter lock-up.

So, from the foregoing you can see that a change in tyre diameter and an engine remap can have effects on the automatic transmission shifting and lock-up behaviour.

“But I don’t have these modifications done to my 4WD, yet it shuffles between gears on hills and the auto transmission temperature gauge rises as a result,” you say.

It’s a commonly heard complaint, but with the few exceptions where OEMs have got their gearing slightly wrong – notably LandCruiser wagons and Isuzu Ute D-MAX Automatics with tall diffs and tall overdrives – this behaviour is caused by the vehicle being asked to do something it’s not really designed for.

Nearly all OEMs design their utes and wagons for emissions compliance and maximum economy as solo vehicles. Only North American utes are designed for heavy towing – hence their popularity, despite horrendous pricing.



Not designed for our needs



Why do Australian-market volume-brand-ute and -wagon owners who tow heavy vans and trailers accept that they’ll have to do various modifications to make these vehicles fit for purpose?

The answer is simple: no-one designs utes and wagons for Australian buyers, because this country is a remote, tiny automotive market. The most popular utes and wagons are not designed to haul 3.5-tonnes trailers and cope with trailer ball weights up to 350kg. We know that most of these vehicles are currently plated to do that, but that was not their original intent.

The intro to the towing section in the 2024 Toyota HiLux owners’ handbook says it quite clearly:

‘Your vehicle is designed primarily as a passenger- and load-carrying vehicle. Towing a trailer will have an adverse effect on handling, performance, braking, durability and fuel consumption.

‘For your safety and the safety of others, do not overload the vehicle or trailer.

‘Toyota warranties do not apply to damage or malfunction caused by towing a trailer for commercial purposes.’



Tradies who haul plant trailers during the working week and camper trailers or boats on the weekend, take note!

It’s by pure chance that North American utes are well-suited to towing Australia’s heavy trailers, because the US towing regime is similar to ours. Europe and Asia – where our medium-sized utes and wagons are designed and made – are quite different, as we’ve explained in the Towing section of this website.



Crawl under a LandCruiser 70 Series V8 or Yank ute and you’ll see what we mean: big engine up front; big light-truck transmission behind that; big chassis; big drive axles; big brakes and big suspension. Put any of the mid-sized utes or wagons beside a 70 or a Yank tank and the comparison is stark.

Incidentally, in the case of medium-sized utes and wagons that are available in both the USA and Australia the trailer-towing ratings for these vehicles in the USA are often less than the ratings they have in Australia. (The 2024 Prado is rated for a 2.7 tonnes trailer in the USA.) Clearly, the towing-oriented US market doesn’t rate some medium-sizers as highly as their Australian distributors do!

Australian medium-sized-wagon and -ute owners willingly accept that they’ll have to do suspension mods to enable their machines to accept heavy trailers with heavy ball loads, but it’s only relatively recently occurred to many of them that the automatic transmissions that now dominate the new ute and wagon markets are also unsuitable for heavy towing work.



Only a few years ago, experienced towing people could pick up a manual-transmission wagon or ute, but not these days. Very few manuals persist and there are none among the popular top-shelf models. 

Internet forums are full of comments about auto transmissions shuttling between torque converter lock up and slip, and high transmission fluid temperatures. There’s a flourishing after-market of electronic devices that alter the OEM’s transmission protocols, to eliminate or reduce the amount of torque converter slip and ratio shuffling.

Our view at OTA has been that such devices void warranties and also cause higher engine emissions, so we can’t recommend them. However, we have great sympathy for wagon and ute buyers who spend lots of money on new vehicles, only to discover that they’re not fit for purpose. The owners are stuck and have to do something.



TC lock-up device on test



To suss out the ramifications of torque converter lock up devices, we bought a Boostec Can Hacker and plugged it into the OTA D-MAX ute. It was a relatively simple plug-and-play installation.



Our shortened-up instructions for use are simple and we’ve put them on a laminated sheet under the dash mat for easy reference:

‘The push button arms the kit for automatic operation. No need to take it out of the auto position. It will lock the torque converter up at 77km/h and unlock at 74km/h.

‘Expert mode: to use the artificial lock up at lower speeds, hold down the cruise-cancel button for one second while driving. To deactivate, tap the cancel button again. Its purpose is for during off-road single gear use, to prevent over heating of the gearbox or to use engine braking while towing under 74km/h. Not to be used at any other time. 

‘Manual gear cruise control: set cruise control as per normal. Select manual shifting and the cruise control deactivates. Tap the res button and the manual cruise is available. To cancel tap the res button again. The gear indicator will stay as D when activated. 

‘Clear limp mode/codes: to clear unwanted codes hit the cruise distance button five times in five seconds.

‘Low range tall gear select: when off road in low range usually only 1st, 2nd and 3rd are selectable. Hit the res button and the taller gears will be available.’

We’ll do some unladen ute driving around town and on the highway, some off-roading and then a long towing trip during August 2024, to see how the unit operates. We’ll report on it in September. 


























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