Please help me understand 4 wheel drive

[Ron045]

We had some snow and wintery mix today in PA. I went out and decided to use the 4 wheel drive high for the first time. I had some trouble and thought you kind folks could help me through it.

I put the vehicle in 4 wheel drive in the driveway. I drove about 3 miles to the grocery store on 35 and 45 mph surface streets that were wet. When I got to the parking lot (also wet) and turned down the row, the vehicle seemed to hesitate. I think I understand that in 4 wheel drive, all 4 wheels want to turn the same. So on a turn I might feel some of the wheels fighting each other. Do I have that right?

When I went to turn into my parking spot, the vehicle just came to a dead stop like it was thrown into park. I tried a little gas and the engine revved a little, but I did not move. I switched to 2 wheel drive and was able to park. I drove home in 2 wheel drive.

Do I have a problem or is this just my inexperience?
Thanks!
Ron

 

[H3LZSN1P3R]

Your not doing anything wrong other than using 4wd on pavement that not slippery… you have to be careful so you dont snap an axle or break anything in the driveline

 

[Rockcrawlindude]

You got it bound up a little. To avoid binding it up, Try to only use 4x4 on slippery or loose surfaces, or in a straight line.

 

[Brutal_HO]

Yup, binding the driveline.

You don't need 4WD on wet roads. The truck has traction control.

These trucks are not like the AWD/4WD on the 1500's.

 

[jkempken]

4WD in these trucks is for more than a couple inches of snow, Mud, and sand that's about it.

 

[MEGA HO]

Yes you got it right and your trucks 4x4 works as designed.
In 4WD all wheels turn at the same speed and it all works good when you're driving in a surface with reduced traction (wet road doesn't really count) or in a straight line. When you're turning, the the inside wheels will have shorter traveling distance comparing to the outside wheels and this is when driveline binding occurs, your wheels will want to skip but being on a surface with good traction makes it hard.

 

[el_barto]

Yes, as others have stated…this is the weakness of 4WD vs AWD in snow. Front and rear driveshafts have to spin at the same speed, but the front and rear wheels travel different distances when turning. On slick surfaces at higher speeds/smaller steering angle inputs it can pretty easily scrub it out with the tires without you noticing*; but lower speeds with greater steering angle input(especially with long wheelbase) you often feel the drivetrain bind until a tire hops releasing the bind.

*i want to add this is another weakness off 4WD vs AWD that most don’t recognize. While you might not notice it scrubbing off the differences in speed in the snow normally (except at lower speeds), it essentially means a tire is slipping. A slipping tire has less grip than a tire that is not

 

[Lary0071]

We had some snow and wintery mix today in PA. I went out and decided to use the 4 wheel drive high for the first time. I had some trouble and thought you kind folks could help me through it.

I put the vehicle in 4 wheel drive in the driveway. I drove about 3 miles to the grocery store on 35 and 45 mph surface streets that were wet. When I got to the parking lot (also wet) and turned down the row, the vehicle seemed to hesitate. I think I understand that in 4 wheel drive, all 4 wheels want to turn the same. So on a turn I might feel some of the wheels fighting each other. Do I have that right?

When I went to turn into my parking spot, the vehicle just came to a dead stop like it was thrown into park. I tried a little gas and the engine revved a little, but I did not move. I switched to 2 wheel drive and was able to park. I drove home in 2 wheel drive.

Do I have a problem or is this just my inexperience?
Thanks!
Ron

And just to be clear, doing what you did on road surfaces that are just wet and not snowy or iced will significantly shorten the service life of the drivetrain and potentially invoke catastrophic failure. Use 4x4 because you NEED it to make it, otherwise... hard no. The half tom Ram trucks have an optional AWD (full time 4x4) transfer case option that allows for use as you attempted. I am not aware of a HD truck with a full time 4x4 option.

 

[Nick]

4x4 causes many people new to the term to come to the mistaken conclusion that all four wheels are powering .Unless you have Lockers in the front and rear or AWD it is one wheel in the front and one in the rear putting power to the ground .

 

[H3LZSN1P3R]

4x4 causes many people new to the term to come to the mistaken conclusion that all four wheels are powering .Unless you have Lockers in the front and rear or AWD it is one wheel in the front and one in the rear putting power to the ground .

Yes and no…. Thats not always true if you include LSD you have 3 wheels spinning and the open diffs will give power to which ever one has the least resistance so you can leave 4 holes even without lockers

 

[Rockcrawlindude]

4x4 causes many people new to the term to come to the mistaken conclusion that all four wheels are powering .Unless you have Lockers in the front and rear or AWD it is one wheel in the front and one in the rear putting power to the ground .

This is a misleading statement, my friend.

 

[Nick]

This is a misleading statement, my friend.

Yes l did overlook limited slip .

 

[Rockcrawlindude]

Yes l did overlook limited slip .

And open differentials.

Open differentials provide equal torque to both wheels.

Lockers provide equal speed to both wheels.

 

[Lary0071]

And open differentials.

Open differentials provide equal torque to both wheels.

Lockers provide equal speed to both wheels.

Correct. What they are missing is that in a perfect world with equal traction and weight and all things being equal, an open diff gives equal force to all tires and all 4 would spin evenly. As traction is added or removed, the wheel with less traction ends up getting the spinning speed, but whatever resistive force (torque bias) is seen by that spinning wheel, the equal torque is applied to the opposite (non spinning) wheel. A Torsen or TrueTrac works by multiplying that force to the wheel with the traction, it is a torque bias multiplying unit.

Unless a wheel is in the air, there is always equal torque left to right in an open differential, the ultimate torque applied is always limited by the wheel/tire with the least traction or resistance since that resistance is what causes the differential torqu application to the other wheel and tire.

A locker cares nothing about torque and biasing, it mechanically locks the rotational speed of the 2 shafts, so you can have zero torque/resistance on one side and all available torque/resistance on the other side and the shafts will spin at exactly the same speed regardless of traction environment.

A clutch type limited slip is not like the Torsen/TrueTrac because it has a pre-set amount of clutch pack pre-load that when the tire on ice attempts to spin free with almost no resistive torque, the clutch applies the preset torque value to the opposing shaft. It does not take resistive torque and multiply it to send to the opposing wheel, it is what it is. In most offroad low traction situations, a TrueTrac out performs a clutch type limited slip in obvious ways to the observer. It looks and acts nearly like a locker until you get a tire in the air. In that case... zero resistive torqu multiplied by anything.... even a million.... is still zero.

For most on-road uses standard diffs work plenty well enough. For more demanding applications, off-road and plowing and such, a Torsen/TrueTrac work amazingly well. But there are drivability differences with the TrueTrac, if you power on into a sharp turn it acts more similar to a locker and tries to plow the steering axle straight ahead. An open differential does not do this and is often considered safer, especially for unexperienced drivers.

I ran a rear TrueTac in my very softly suspended Wrangler JK rock crawler, and on paved roads I could turn and punch it and hang the inside front tire a foot or so in the air as the tires howled from the TT doing its thing. It made a fun show.

I will say that any time I had to wheel with a Jeep on open diffs at Rausch Creek.... I cringed. I knew I would spend my day getting him through things that I could do in 2WD.

 

[el_barto]

4x4 causes many people new to the term to come to the mistaken conclusion that all four wheels are powering .Unless you have Lockers in the front and rear or AWD it is one wheel in the front and one in the rear putting power to the ground .

Well yes, but actually no.

In normal driving (straight, flat road with good traction in 4WD), each wheel will receive 25% of the torque. An open differential is capable of transmitting equal amounts of torque to both sides.

Let’s look at a RWD, open differential system. Under normal operation, where the tires are capable of transmitting all the torque to the ground…If there is 100 torque units available at the differential each wheel gets 50 torque-units. If one wheel is on a less grippy surface and it can only support 25 torque-units before slipping, then the other side (still on the grippy surface, also only gets 25 torque units. If the tire has no resistance (in the air/on glare ice) it can support zero torque, and thus the other side also gets zero torque units.
So you’re thinking “no the open diff sends more power to the less grippy side”. Wrong. It sends equal torque to both sides, but the torque is limited by the traction on the side with the least resistance. So you say “but my Cummins has 1000 torques where did they all go???” …torque is a function of force, and force has an equal and opposite. The road (traction) in this case is the resistive force. The engine may be capable of 1000torque units , but it isn’t producing that many if it doesn’t have a resistive force (traction).

I have always struggled to wrap my head around the differentials concept, so hopefully this explanation was helpful.

 

[dm6]

Help me understand this as well. I do understand that you shouldn't use it on dry pavement because of the binding issue, but I have a question to those that say just to use it when you need it or when you are stuck. Is it not a good idea to just use it whenever there is snow on the road? You probably don't need it when driving on a flat road with compact snow, but does it hurt? Like even on the freeway, if there is compact snow (even with on occasional bare spot) and you are going 40 mph, while you aren't going to get stuck, won't this still help your steering if you happen to hit a slicker spot on a slight curve, or not? I guess I have just always put my trucks or SUVs into 4WD when driving on compact snow "just in case". That being said, I also understand it can cut down on fuel efficiency (maybe it doesn't matter with these gas hogs) so if there is no benefit to driving on a freeway with compact snow, then I won't do it.

On another note, I recall hearing somewhere in the past that you should engage 4WD throughout the year every so often. Is that the case with this too?

 

[Lary0071]

Help me understand this as well. I do understand that you shouldn't use it on dry pavement because of the binding issue, but I have a question to those that say just to use it when you need it or when you are stuck. Is it not a good idea to just use it whenever there is snow on the road? You probably don't need it when driving on a flat road with compact snow, but does it hurt? Like even on the freeway, if there is compact snow (even with on occasional bare spot) and you are going 40 mph, while you aren't going to get stuck, won't this still help your steering if you happen to hit a slicker spot on a slight curve, or not? I guess I have just always put my trucks or SUVs into 4WD when driving on compact snow "just in case". That being said, I also understand it can cut down on fuel efficiency (maybe it doesn't matter with these gas hogs) so if there is no benefit to driving on a freeway with compact snow, then I won't do it.

On another note, I recall hearing somewhere in the past that you should engage 4WD throughout the year every so often. Is that the case with this too?

The old going into 4x4 a few times a year was because we had locking hubs that would be in the "free" position for many months and the driveshaft had greased U-Joints that were not turning as did the front axle shafts. This no longer applies since we are always spinning our axles and always spinning our driveshafts, the front driveshaft is just disconnected inside of the transfer case on these newer trucks. In my opinion this is a downgrade from the old trucks, but in the dumbing down of the human race and likely as a means for cost saving at the manufacturing level... we pay to drag a few hundred lbs of steel around and rotating it at all times so that men do not have to get cold fingers locking hubs and axle assemblies can be built without the "complexity" of locking hubs. They aren't that complex....

 

[Rockcrawlindude]

The old going into 4x4 a few times a year was because we had locking hubs that would be in the "free" position for many months and the driveshaft had greased U-Joints that were not turning as did the front axle shafts. This no longer applies since we are always spinning our axles and always spinning our driveshafts, the front driveshaft is just disconnected inside of the transfer case on these newer trucks. In my opinion this is a downgrade from the old trucks, but in the dumbing down of the human race and likely as a means for cost saving at the manufacturing level... we pay to drag a few hundred lbs of steel around and rotating it at all times so that men do not have to get cold fingers locking hubs and axle assemblies can be built without the "complexity" of locking hubs. They aren't that complex....

This isn’t really correct. The driveshaft is disconnected at the T-case but The driveshaft doesn’t spin during normal (2wd) operation. This is because of the axle side disconnect.

The long side axle shaft has a disconnect, so the r&p, hubs and stubs are spinning but the driveshaft doesn’t.

How does the r&p spin but not the driveshaft? Open diff. The stub shaft spins backwards. If you put an open diff vehicle on jack stands in park and spin a tire, the opposing side turns backwards even though the vehicle is in park.

You can verify this by laying under your truck and spinning the front driveshaft with the truck in 2wd/park, axle is disconnected from driveshaft

 

[MEGA HO]

Help me understand this as well. I do understand that you shouldn't use it on dry pavement because of the binding issue, but I have a question to those that say just to use it when you need it or when you are stuck. Is it not a good idea to just use it whenever there is snow on the road? You probably don't need it when driving on a flat road with compact snow, but does it hurt? Like even on the freeway, if there is compact snow (even with on occasional bare spot) and you are going 40 mph, while you aren't going to get stuck, won't this still help your steering if you happen to hit a slicker spot on a slight curve, or not? I guess I have just always put my trucks or SUVs into 4WD when driving on compact snow "just in case". That being said, I also understand it can cut down on fuel efficiency (maybe it doesn't matter with these gas hogs) so if there is no benefit to driving on a freeway with compact snow, then I won't do it.

I've always had my personal and work trucks in 4WD in winter time after snowfall or whenever the roard were slippery, driving up to 100-120kmh. It helps keeping the truck straight otherwise you're risking seeing your arse trying to pass you every now and then.

 

[el_barto]

Help me understand this as well. I do understand that you shouldn't use it on dry pavement because of the binding issue, but I have a question to those that say just to use it when you need it or when you are stuck. Is it not a good idea to just use it whenever there is snow on the road? You probably don't need it when driving on a flat road with compact snow, but does it hurt? Like even on the freeway, if there is compact snow (even with on occasional bare spot) and you are going 40 mph, while you aren't going to get stuck, won't this still help your steering if you happen to hit a slicker spot on a slight curve, or not? I guess I have just always put my trucks or SUVs into 4WD when driving on compact snow "just in case". That being said, I also understand it can cut down on fuel efficiency (maybe it doesn't matter with these gas hogs) so if there is no benefit to driving on a freeway with compact snow, then I won't do it.

On another note, I recall hearing somewhere in the past that you should engage 4WD throughout the year every so often. Is that the case with this too?

Driving in 4Hi on packed snow or mixed conditions on the highway is fine. Yes you do absolutely gain cornering traction having it in 4WD.

I try to limit my speed to 55mph in 4WD, and not shift to 4WD above 40.