I am new to owning a 4 x 4 truck can someone please tell me when I should be using 4h and 4L? Sorry for my ignorance but I have heard a lot of people say use 4 x 4 in the rain or use it every now and then as a practice for maintenance ..... when should I be using four-wheel drive mode and when should I not be using four-wheel drive mode on my new super duty

 

4 high is for say speeds above 15mph
4 low is when it shifts the transfercase into very low gearing with a high ratio meaning your RPMs could be at 4,000rpm but your only going 10mph max speed. You'll have max power in 4 low.

A good time to use 4 low is if you have a giant boat and your trying to pull it out of a steep boat ramp, pop it in 4 low and there is less stress and easier to pull the boat out.

4 high you'll want to use at highway speeds if needed.

Just flip it to 4 low quick and go for a drive around the block, you'll see what i mean about your max speed being limited.

 

4 lo is for extreme traction and power. You are very limited in 4 lo. Speed of any kind is not really possible. Shifting to 4 lo requires transmission be in neutral. 4 hi can be shifted on the fly so to speak but should not be driven on dry roads.

4 lo is a crawling gear set.

It is doubtful most people will ever need or use 4 lo.

 

Only use 4x4 (Hi or Low) when driving in snow, or when driving on a low traction surface such as a dirt road, mud, or driving off-road.

Don't use 4x4 when driving on dry, paved roads unless you are driving in a straight line.

4x4 Low was designed for off-road use, when trying to make a very steep climb so as to have the best possible control and not needing high speed. It was developed when 4x4 vehicles such as the original Jeep and Land Rover from the 1940's had very little power. Nowadays, it is useful for moving a very heavy load in low traction conditions at slow speed with easy throttle control, or useful for descending steep grades off-road, or still ascending steep slopes off road.

Contrary to popular belief, 4x4 Low does not give you any more traction or better grip than 4x4 Hi.

The low range just uses another reduction gear in the transfer case to supply extra oomph to the wheels. Currently, the reduction is 2.64:1, meaning low range is a little more than twice the torque output of high range or 2WD.

The previous generation had a 2.72:1 low range reduction. For perspective, Jeep Wrangler Rubicons had a 4:1 reduction.

Most people will never use 4x4 Low. But nothing wrong with getting into some dirt and experimenting. Or experimenting on pavement in a straight line.

 

About the only time I use 4 LO is when I'm on a dirt/gravel road that is very steep, and I'm going down hill. It saves the brakes and adds to control. (And I only use it in my work truck, because I never get my POV in that situation. )

 

The only time I put my truck in 4 lo is when I am backing my fifth wheel into the garage just so it's very slow and I don't have use any pedal to move. I have about 1.5" on either side when going through the door on a 41' long trailer so I don't want speed

 

It was to my understanding that low locked the limited slip thus all wheels turn evenly where as 4 high engages all wheel drive but still allows differential rotation.

Spinning in high you will see some wheel rotates faster then others. 4 low they all are equal.

Is this correct?

 

No. 4hi and 4lo both lock the transfer case, so the front rear split is 50/50. The difference between Hi and Low is the gear reduction.

Some models have an electronic locking rear axle, that when engaged locks the rear wheels to the same rotation.

Unless added aftermarket, there is no front limited slip or lock. So you can at max from the factory have a 3x4 drive.

The front hubs have both an automatic (vacuum operated) engagement as well as a manual engagement. They accomplish the same thing, but the vacuum operation is prone to failure.

I use 4lo when driving on the beach because I am not going real fast and I prefer the way it handles the deeper sand, plus I seem to have less axle wrap in low than hi.

 

I want to emphasize what was stated earlier. 4x4 is okay to use in dirt, mud and snow. Do not use your 4x4 on the pavement even in the rain. There are a few situation where you can but only drive straight DO NOT TURN while in 4x4 on pavement. You will bind you front axles and can do damage to your front differentials.

I personally like to use 4H any time I get on a dirt road even if its a scraped and maintained road just to keep everything lubed up and working properly. 4L is for pulling another vehicle out of a ditch or for slowly climbing up flag poles.

 

I have always learned not to use 4hi on the pavement unless 100% necessary. IE: snow.

4lo never on the pavement.

 

Would it be advisable to run in 4 high on a rainy highway?

 

I wouldn't. I don't see a need. If it was literally a monsoon, with water running over the surface of the road, maybe then.

Modern tires perform very well in the rain. If you can brake hard on wet pavement, and the truck doesn't skid, you should not be using 4x4.

 

gotcha thanks

 

^^Exactly right.

I would add that when 4x4 is engaged, brake-based traction control is now available on the front wheels, as well...so theoretically, you could move even if only one (front) wheel had traction.

Duallys (like mine) can be optioned with a limited slip on the rear, but cannot have the locker. I've been pleasantly surprised to find the limited slip in this new Dana axle seems to work much better than expected.

Pretty interesting thought on the axle wrap in 4x4 high vs 4x4 low. I had to crawl through some snow this winter towing snowmobiles, and kept braking through the crust on top. Pretty bad axle wrap. Next time, I might try low range.

 

No problem. Its also one reason folks sometimes wish for a clutch-based "automatic" 4x4 system like what is found on the half-ton trucks. You may be driving on a section of roadway covered with snow, but at times the road becomes completely clear or partially clear. So you either have to run in 2WD or risk damage by running continuously in 4x4, or annoyingly having to keep switching in and out.

Keep in mind the 4x4 systems on these trucks are very durable, and just because you intentionally or unintentionally use 4x4 when you shouldn't doesn't mean something is going to break. I know people that have driven 30 miles on dry pavement with 4x4 accidentally left engaged...truck sure smelled hot...but nothing broke. Certainly not advisable though.