Have you used 4wd Low on public roads and highways?

[John E Davies]

I am unafraid of using the full capabilities of my truck.

 

We drove north from Fruita CO on a very hot afternoon heading to Dinosaur National Monument and stumbled across the wonderful Douglass Pass. It is a set of hairy switchbacks dug into the end wall of a precipitous box canyon. It is neither high nor steep compared to many others in Colorado, but it is challenge pulling a trailer due to the VERY tight turns, average 7% grade and no guardrails. Plus semi-truck traffic. It has a 20 mph speed limit and you can’t maintain momentum through the turns.

 

Rather than struggle up in first gear while straining the drivetrain, I pulled over and engaged 4 Low and went up it t 4000 rpm in fourth gear, at up to 30 mph on the straights. Transmission torque converter and pan temps, and engine coolant temp remained normal, using my Scangauge, and I felt in full control. The truck felt happy and under no strain.

 

All these really hard passes have a pulloff at the top for viewing the scenery or fixing your broken car, so it was easy to pull over and get out of 4 Low, and also take a lunch break while absorbing the beautiful scenery.

 

I have used 4 Low a few times before while towing up or down super steep Idaho switchback backroads, up to 18%, but never before on a busy highway with other traffic.

 

Anybody else done this? I was very pleased with it in this particular situation. It would not work if you had to drive much over 35 mph, and you must plan for a place to stop at the top to get back into High.

 

Let’s hear your stories.....

 

Caution: you can only do this on high traction surfaces if your truck has a center (third) differential like my Land Cruiser, or you may cause very serious damage to the system. The front and rear axles must be allowed to turn at different speeds .... https://sites.google.com/site/awdand4wd/

 

This is something to consider when buying your next tow vehicle....

 

John Davies

 

Spokane WA

[Rleog]

A couple of questions.  What's the towing capacity of your Land Cruiser, and do you have an engine oil temp gauge (if so, what were the temps)?

 

Bob G.

[John E Davies]

A couple of questions. What’s the towing capacity of your Land Cruiser, and do you have an engine oil temp gauge (if so, what were the temps)?

 

Bob G.

 

Hi Bob, it is rated at 8300 pounds trailer, 850 pounds tongue weight, I have 2 inch oversized LT tires which lower this number  a little. Axles are 3.90 (higher than the Tundra's 4.10). The trailer is typically about 6000 pounds loaded.

 

I do not monitor oil temp, though it is possible to do it with the Scangauge. ... https://www.scangauge.com

 

The transmission oil pan temp normally runs around 195 F, the same as the coolant temp, slowly spiking to 205.

 

The torque converter temp is normally the exact same as pan temp when the converter is locked, but it quickly spikes to 220 when unlocked on short climbs and 230 on long climbs. The highest I ever saw it was 235 for a short period on a really nasty grade. I am running Toyota ATF which I believe is semi-synthetic. I plan to do a full flush and service with full synthetic ATF.

 

The 200 has a seriously overbuilt cooling system, you would really have to try very hard to hurt the truck. It is a tank - keep the fluids and filters changed and it will run forever, and take you through hell and back again..... unlike the older 80 Series I used to own, you never have to worry about coolant temps.

 

John Davies

 

Spokane WA

 

 

 

 

[mountainoliver]

Not on hard surface roads but many times in snow or in muddy or wet grassy fields with my old truck. Once pulled out a utility trailer loaded with 15 fairly new cross ties and 15 in the truck bed. (Roughly 300 lbs each x 30) Old truck 1996 Dodge 3/4 ton, 12valve Cummins, and 4x4. There was a modification to that truck to enable two wheel drive low. Which is ideal in situations such as you described. When we bought our Oliver we also bought a new Tundra 4x4 with the 5.7L engine. More refined than the old Dodge. I don’t think the Tundra has the center differential. I do sometimes miss that old Dodge though!

[John E Davies]

Old truck 1996 Dodge 3/4 ton, 12valve Cummins, and 4×4. There was a modification to that truck to enable two wheel drive low. Which is ideal in situations such as you described.

Ideal except that is a good way to blow out the rear driveshaft u-joints. That is a heck of a lot of torque going through just one shaft and one axle. I would really worry about it ....  but those old Cummins are great engines.

 

I tried to find a list of full time 4wd trucks and SUVs with a transfer case, that allow use of low range on pavement, but came up empty. Can anyone provide a link? Maybe the Grand Cherokee with QuadraTrac II?

 

John Davies

 

Spokane WA

[Rumline]

On my Jeep, 4 Low locks the center differential, which from my understanding is not good to do on pavement.  I've got this nice warning in the owners manual:

 

Do not drive in 4WD-LOW Range on dry pavement;

driveline damage may result. 4WD-LOW Range

locks front and rear drivelines together and does not

allow for differential action between the front to rear

driveshafts. Driving in 4WD-LOW on pavement will

cause driveline binding; use only on wet or slippery

surfaces.

 

Does your Land Cruiser's 4L operate differently?

[John E Davies]

On my Jeep, 4 Low locks the center differential, which from my understanding is not good to do on pavement. I’ve got this nice warning in the owners manual:

 

Do not drive in 4WD-LOW Range on dry pavement; driveline damage may result. 4WD-LOW Range locks front and rear drivelines together and does not allow for differential action between the front to rear driveshafts. Driving in 4WD-LOW on pavement will cause driveline binding; use only on wet or slippery surfaces.

 

Does your Land Cruiser’s 4L operate differently?

Yes, it has a Center Differential Lock switch on the dashboard, so it can operate in either High or Low Range. It is completely controlled by the driver. I sometimes lock the center diff in High Range when ascending steep gravel forest roads that have a lot of washboard switchbacks, it is helpful and reduces wheel-spin. It does turn off ABS when engaged.

 

 

There might be a way to fool your Jeep’s transmission computer, check on the Jeep forums for a “center difflock disable” electrical mod. If you can turn that off, there would be no reason to avoid using Low on hard surfaces. It might be as easy as installing an on-off switch in the wire coming from the transfer case sensor, I dunno.... or there may be a computer hack or dealer setting that can be altered. If it is possible, somebody has already done it, and documented it.

 

Good luck.

 

John Davies

 

Spokane WA

[Raspy]

John,

 

 

 

Low range with the center diff unlocked seems perfectly sensible to me.  A higher RPM will allow the engine and tranny to cool well, or possibly generate less tranny heat, and the engine can be right up in it's max torque range.  If possible it would be good if the torque converter was locked to make less heat.  An automatic trans should never overheat with the torque converter locked.

 

You could even do it with the center diff locked, if you had to for traction, but it would add more stress and tire wear.

 

I really like that you have a button to lock or unlock the center diff in either low or high range.  Cool.

 

Two wheel low is a cool mod that works well on older Dodge Cummins trucks with the auto trans. This is because the first gear in the tranny is pretty high and the transfer case is only 1.98 to 1 in low.  With 2wd low much less heat is developed in the tranny and more precise maneuvering can be done. The torque through one axle is not a problem, especially with the auto trans.

[John E Davies]

I thought I would revive this dusty old thread .... I saw this $150 plug and play kit for late model Rams: engage 4 Low and flip the switch to keep the front axle UNLOCKED. For maneuvering a trailer at low speeds, or ascending steep low speed grades, this would be very useful.

https://www.genosgarage.com/product/dodge-ram-cummins-bd-1030705-2-low-unlock-front-differential-kit/switches-sensors-drivetrain

John Davies

Spokane WA

Edited February 26, 2020 by John E Davies

[BackofBeyond]

Very rarely. I believe the darn thing in low would pull until it tipped over on its back. I only like to engage off road.  But it is nice  to know there is an option.