great advice thank you

 

I know guys who run 4x4 in their trucks all winter long on dry pavement and everything. Mostly company trucks. While I am sure it's not good for it I have never seen anything explode or out right fail on the components. Is it not possible some are over cautious and some are under when it comes to 4x4

 

Are you sure they are not just running their front hubs locked in all winter, but only actually engaging 4x4 at the transfer case when needed? That is indeed harmless.

"Part-time" systems like what the HD trucks all have cannot vary speeds *between* the front and rear axles when they have 4x4 engaged. If you drive in fresh snow and make a turn, you will see the problem. All 4 wheels leave slightly different tracks. That means all 4 wheels are traveling at slightly different speeds, because some have to cover more distance or less distance relative to one another.

The front and the rear differential allow for the needed variation in speed *across* the axles, but the rear wheels will travel at a different speed than the front wheels while making turns. Vehicles with "permanent" or "full-time" 4x4 such as a Toyota Land Cruiser, a Land Rover Range Rover, Porsche Cayenne, Mercedes G550, etc, etc have a third, center differential. This is used to allow that different speed between axles even when power is applied to front and rear axles together. Part-time 4x4 vehicles do not have this feature.

So you can imagine the problem...a vehicle with part-time 4x4 engaged makes a turn on dry pavement. Because the rear wheels have more distance to cover than the front, they have to speed up...but they can't, because 4x4 is engaged, locking the front and rear wheels together and forcing them to turn at the same speed.

What happens? In a slight turn, the driver would feel some extra resistance, some extra pressure would be put on the drivetrain, and the tires would likely wear quicker. In a sharp turn, the tires would bark and chirp and the vehicle would hop and bind. Doing this repeatedly would likely blow a u-joint first, probably a front axle joint, maybe a driveshaft u-joint. If this was repaired and this practice continued, I would expect eventual damage to the transfer case or the axle half shafts.

So while you may not destroy your truck overnight by using 4x4 incorrectly, you will eventually damage the components I mentioned.

If all you drive is dirt roads, by all means, leave 4x4 engaged continuously. No harm done.

The reason why part-time 4x4 "works" on low traction surfaces like snow, ice, dirt, sand, mud...etc...is because the low traction allows the tires to "slip" to make up the speed difference.

Part-time 4x4 can be very strong; it is cheaper to make, lighter, and works well. The driver just needs to understand how 4x4 and differentials work, and what is appropriate use and what is not.

 

In simple terms, the difference is the gear ratio through the TC.

4H is 1:1
4L is 2:72:1

 

Hope you got the information you wanted. 4 WD low is for slow speed operation. It is about gearing and traction when you need it. It can save the transmission. I once saw a guy make his E4OD transmission puke while backing a heavy gooseneck up a grade. The 7.3 had the torque to move the truck but it was too much for the transmission and it puked the fluid. He later told me that someone had told him to never use 4WDL. A damn expensive bit of ignorance on his part.

 

4L is 2.64:1 for 2017 trucks.

 

A perfect time for 4 wheel drive low is moving a trailer onto levelling blocks. This works well two ways: if your trailer spot isn't level it probably is paved either and the added traction from four wheel drive will help; and secondly the additional torque from the low gearing will reduce the transmission strain. For the few seconds it takes to engage, you could be saving yourself from transmission trouble in the future.

I also believe this things should be used periodically to reduce a seize up risk.

 

Interesting input here. I always thought 4low locked in the drivers side wheels.

It did on my GM trucks. I've been in many snow situations trying to pull cars out of snow banks etc. 4hi just spun both the front and rear passenger wheels. But in 4low, I had all traction incl the drivers side.

So the Ford is apparently different, since I don't drive my F350 in the winter, I might never found out this valuable info. Thanks!

 

All of this is very good information.

If you're not familiar with 4WD then read the manual and practice using it so you know how when you need it.

Besides that, RTFM!

 

Thanks everyone good stuff. I did check out TFM lol and watched the online videos on ford website but it was not very informative for real life situations. All of your real life examples help greatly to illustrate the use for me

 

The GM trucks don't work any different. The *only* thing low range does on any vehicle is add a reduction gear. Nothing is getting locked or does anything special.

You have to understand the concept of a differential. All Ford, GM, and RAM full-size trucks use an "open" front differential, with the exception of specialty trucks like the Raptor (Torsen) or PowerWagon (locking). An open differential simply means power will *always* travel to the path of least resistance. In other words, all the power will go to whichever side has less traction. So in your example, 4Hi was sending power to both the front and rear axle but the front and rear differentials were finding less traction on the passenger side and all the power was sent there. You engaged 4-Low and found that the driver's side was spinning. In this case, traction was probably pretty equal between the wheels (you said you were in snow) and so the power happened to shift to the driver's side or maybe the traction was equal enough to where power was sent to both the driver and passenger side. It had nothing to do with 4-low.

Here's the classic example: If you are in rear-wheel drive and have an open rear differential (no locker or limited slip device) and are parked facing slightly uphill...and one wheel is on a patch of ice and the other wheel is on dry pavement...only the wheel on the ice will spin. Likewise, if you re driving off-road, and the suspension articulates to the point that one wheel is in the air and the other is on the ground...all the power will go to the wheel in the air.

So you can see where a locker or limited slip or even brake-based traction control would be very useful...because it is a method of transferring some of the power across the axle to the side with (presumably) more traction.

 

4 hi in the rain?
Seriously?
Maybe if you are crossing a washout that's filled with mud and moving water.

 

We've never run 4x on just wet surfaces, it's either wet grass and not wanting to fill the rear siping and start spinning up the yard, or as mentioned... the ugly word (snow).

The assumption that the front spins just a tad faster (revolution wise) than the rear was a wear factor that I don't think would be good on any traction like surface.

 

I'll have to read this thread again and a lot of good info.
Quick (dumb) question. Is 4LO ok to use in reverse? I see a lot of implied forward movement "while driving" "taking a boat out" etc. (Took liberty with the quotes). Also in 4Hi?

 

You can use 4w-lo or 4w-hi in reverse in boat launches or recovery with wheels straight, do it all the time.