4x4 on pavement

[captainhero]

Hi
Dumb question - when I engage 4x4 and driving on pavement, the truck really jumps around when turning. I know I'm not supposed to do that (you know you have to try what you're not supposed to be doing !!) but i'm wondering if it's expected to have such an outcome ?

 

[fastpakr]

Yep, that's the normal behavior.

 

[RonD]

Yes, normal

4WD is not the same as AWD

AWD uses a fluid coupler between front and rear drive shafts, this sends 30% of power to front wheels and 70% to rear wheels
And it allows "slipping" between front and rear drive shafts

4WD connects front and rear drive shafts together, directly, 50/50 power split
When you are going straight, assuming tires are the same size(diameter), there is no real issue, although not recommended on pavement because tires are NOT EXACTLY the same size because of wear and tire air pressure.

When steering front wheels one way or the other too much, the outside wheel needs to spin much faster, to cover more ground, than the inside wheel, so you get that "jumping" of one wheel trying to match revolutions with the other wheels
You can feel it on gravel or dirt as well but not nearly as much as on dry pavement, because wheel can slip on loose material

 

[wildbill23c]

Hi
Dumb question - when I engage 4x4 and driving on pavement, the truck really jumps around when turning. I know I'm not supposed to do that (you know you have to try what you're not supposed to be doing !!) but i'm wondering if it's expected to have such an outcome ?

There's your answer to your own question. Its a part time 4WD system its not supposed to be used on dry pavement. Some systems are a bit more forgiving than others as to how they react being driven on dry pavement in 4WD, some are not forgiving...I've found the older 4WD's would really hate being driven and turned on dry pavement in 4WD, some newer vehicles it seems they're more forgiving in those situations....the trouble is they're not designed for it, and if done a lot it'll damage drive train components. Along with that, you are causing more wear to your tires as they have to skid and spin in order to move the vehicle and a lot of excessive force is applied through the whole drive train to get the vehicle to move in a turn in 4WD on paved surfaces. Even a wet road isn't really enough slippage to allow usage of many part time 4WD systems without some serious binding occurring....throw in a vehicle that has a limited slip differential and the problem is worse LOL.

Stick to 2WD on dry and wet pavement, save the 4WD for the snow/ice, sand, mud, etc. HAHA

 

[captainhero]

Thanks for the answers. I knew it would put stress on the drivetrain, I was just surprised by how much it fights back.

 

[captainhero]

When steering front wheels one way or the other too much, the outside wheel needs to spin much faster, to cover more ground, than the inside wheel, so you get that "jumping" of one wheel trying to match revolutions with the other wheels
You can feel it on gravel or dirt as well but not nearly as much as on dry pavement, because wheel can slip on loose material

But isn't that what a differential is supposed to be helping with ? is there no differential on the front axle, or is it more complicated with the steering being involved ?
Just trying to understand the physics in play.

 

[RonD]

Yes, and the front differential is OPEN

But..........the easiest wheel to turn, the one spinning faster, gets all the power and its connected to the REAR wheels in 4WD so.......revolutions are different, and as said there is no differential in the transfer case, its a direct connection between the two drive shafts
And a differential, even an OPEN one, still effects the slower moving front wheel

 

[sgtsandman]

The system binds up if there isn’t enough wheel slip because of the direct connection in the transfer case. That is why you are getting the bucking and why using 4X4 on wet or dry pavement is not recommended. You will run into the same thing in 4 Low, even off road if there isn’t enough slip. You drive it enough in different conditions, you’ll learn when to use each selection.

 

[ericbphoto]

Thanks for the answers. I knew it would put stress on the drivetrain, I was just surprised by how much it fights back.

Eventually it loses the fight and then your bank account gets sad.