If you're going in a straight line, all four tires are turning the same speed. If you're turning, the tires on the outside turn faster than the tires on the inside. The 4WD drivetrain in our trucks "locks" the tires together so that the tires can't turn at different speeds. If you try to turn with 4WD engaged, the tires will apply differing forces on the differential because they're trying to turn at different speeds. That's what causes the binding. This is a problem when you have lots of traction. If the surface is slippery--snow, slick road, ice, etc.--then instead of applying differing forces on the differential, the tires will just slip. That's why it's OK to use 4WD and turn when it's slippery.

I rarely need 4WD where I live, but every few weeks I engage 4HI and 4LO just to exercise the drivetrain. If I'm on dry pavement, I just roll straight forward and back a few times.

 

Great explanation everyone! Thank you. Learned something today about 4WD systems...

 

No, 4x4 is not made for rain.
You've already commented that you have never ever used 4x4 in your life. You've made it through many rain days with no problem. Do not start using 4x4 in the rain. There is not enough slip to not cause premature wear on the drive line.

Using 4lo to pull a boat from the water is nice because you get the gear reduction.

 

If you have Auto 4WD you probably will never need any of the other modes.

 

Does this mean that 4WD only engages when sensors detect slip? If so, isn't 4a more like AWD systems in SUV/CUVs then?

 

Very Close. There is a pretty good YouTube video on a real world test actually in snow where you'd think regular 4WD would be better but Auto 4WD turned out to be better. There is a useful dash screen to watch what wheel gets power when in auto 4WD mode.

You can also add Auto to 4WD without it. There is a write-up on it on this forum somewhere.

 

In 4A the front hubs are locked in but the transfer case uses a clutch system to activate/de-active based on a bunch of different parameters. So yes and no lol

 

True 4X4 is an old technology intended for harsher off road, low traction situations or deep snow on pavement. There are very few times when it is acceptable to drive in 4X4 on pavement, even wet pavement. Pulling a boat up a slick boat ramp is about it. 4X4 should be used sparingly even off road. If you're on hard packed dirt it is the same as pavement. Only use it on surfaces where traction that will easily allow a wheel to spin.

When you corner the inside wheels are going to try to slip slightly on the ground since they are moving at the same speed, but traveling less distance. If you're on sand, loose dirt, gravel, mud, snow or something similar the wheel will spin slightly and do no damage. If traction is good you risk breaking internal parts.

AWD is a newer, smart system that will sense where traction is needed and allow power to go to all 4 wheels and at different speeds. It is also more expensive, and while it works great on wet or dry pavement, light snow or mud, it doesn't work as well in harsher conditions or deep snow.

The owners manual recommends about 10 miles/month in 4X4 to keep the parts lubricated and to ensure the electrical parts function. Some guys will advise that it is OK on pavement as long as you don't take any sharp corners.. This is why I don't like to buy a used 4x4. I wouldn't touch one with a 10' pole if I knew the previous owner had done this. The damage is cumulative. It is rare for parts to break instantly. But over time the excessive wear will cause a premature failure. Just about everyone has forgotten to shift out of 4X4 after getting on pavement. Don't panic if you do, just get back into 4X4 ASAP and try to avoid it.

If you let the 4X4 system go unused for months at a time you risk it not working when needed. I had it happen 25 years ago and have seen others have the same issue. It isn't always practical for me to get to a dirt or gravel road every single month, but I won't go longer than 2 months. Most of the year I'm on a dirt road almost weekly. I'll shift into 4X4 for even a short distance of less than a mile if that is all I have, better than nothing. Other months I may log several hundred miles in 4X4. The key is use it or lose it.

 

Is it okay to use 4A to achieve this same "maintenance" task for the 4WD system? This is why I did not want 4WD on my truck, but to get the options I wanted, I had no choice.

 

Could someone tell me which section of the owners manual says to use 4wd 10 miles a month, or any minimum use? I couldnt find such mention in the 4wd section of my 2019 manual.