Why no 4 wheel drive on roads?

[DieselBound]

apologize for the obvious, to relieve my '92 4x4 toyota pu switching back to 2wd, i come to a full stop, reverse & it will usually do the trick
on the tractor, either by reversing, or by slightly lifting the ft end w/FEL will disengage a stuck 4wd. thinking my limited slip ft end also helps w/the 4wd binding. love the higher end M series...

My Polaris also will get locked into 4wd such that I have to reverse and then switch to 2wd to release 4wd. Seems like physics is in play with everything

 

[ljjhouser]

My first experience driving a 4wd vehicle was in 1976. We had an IH Scout. Had to get out and lock the front hubs for 4WD. The instructions back then were to avoid driving in 4WD on dry pavement. I'm no engineer, but I don't think it is just a tractor thing.

In 1995 (seems like yesterday) I bought a Ford Bronco full size ( I think that was the last year for them). It had "self locking hubs on the front. I did not like them, you could never tell for sure if they were locked or not. Seemed that they wouldn't lock until they would slip. Too late them, stuck. I changed them to Mile Marker manual locking hubs. Liked that much better.

 

[ning]

In 1995 (seems like yesterday) I bought a Ford Bronco full size ( I think that was the last year for them). It had "self locking hubs on the front. I did not like them, you could never tell for sure if they were locked or not. Seemed that they wouldn't lock until they would slip. Too late them, stuck. I changed them to Mile Marker manual locking hubs. Liked that much better.

The only unreliable thing about my '97 F350 was that the autolock hubs (the left one, actually, for whatever reason) failed twice in 170k miles.
Now I've got the good old fashioned manual hubs too. Lock them if there's any hint I'll want 4wd, maybe I'll remember to unlock them by summer...

 

[ruffdog]

It's called transmission wind-up and there can be a tremendous amount of torque induced into the driveline.

 

[CausticUrbanCoast]

Odd segway to diesel-electric drivetrain.

It is unlikely to happen, that is why hydraulic final drives exist. Too expensive for most compact tractors though, at that price point people buy a skidsteer or telehandler instead.

 

[Farmer495]

Tractor: Front wheels lead (turn faster) so you are binding up the drivetrain and the front tires either slip or something lets go in the driveline.

Loader tractors used on concrete floors scraping alleys in barns that run in 4wd all the time tend to wear the front tires bald in a hurry.

You will feel the bind if you leave tractor in 4x4 on dry pavement.

The binding is considerably noticeable at faster speeds. Have an operator's manual for one tractor that clearly states not the use 4wd in higher gears.

I do a lot of road travel, hundreds of km a year, all in 2wd. Icy or snowy roads I will use 4wd if I need the traction.

Pickup Truck: Front wheels normally turn same speed as rears, you can drive as fast as you want, shift in and out of 4wd on the fly on most newer trucks. Try to turn a corner on dry pavement and you will feel it....

 

[k0ua]

Tractor: Front wheels lead (turn faster) so you are binding up the drivetrain and the front tires either slip or something lets go in the driveline.

Loader tractors used on concrete floors scraping alleys in barns that run in 4wd all the time tend to wear the front tires bald in a hurry.

You will feel the bind if you leave tractor in 4x4 on dry pavement.

The binding is considerably noticeable at faster speeds. Have an operator's manual for one tractor that clearly states not the use 4wd in higher gears.

I do a lot of road travel, hundreds of km a year, all in 2wd. Icy or snowy roads I will use 4wd if I need the traction.

Pickup Truck: Front wheels normally turn same speed as rears, you can drive as fast as you want, shift in and out of 4wd on the fly on most newer trucks. Try to turn a corner on dry pavement and you will feel it....

Yes, unless you have a vehicle with a viscous coupling between front and rear driveline. Example Chevrolet Silverado of mine has an "Auto" setting on the 4WD selector. The idea is you can drive on a road that is dry is some places and maybe a little icy in others. You need 4WD one second and don't the next. It works pretty well, and prevents torque windup, but does throw torque toward the front driveline when needed. Of course it "eats" some fuel mileage. So you don't want to run in it all the time as 2WD will give better gas mileage. But our CUT tractors have nothing like that.

 

[ptsg]

Yes, unless you have a vehicle with a viscous coupling between front and rear driveline. Example Chevrolet Silverado of mine has an "Auto" setting on the 4WD selector. The idea is you can drive on a road that is dry is some places and maybe a little icy in others. You need 4WD one second and don't the next. It works pretty well, and prevents torque windup, but does throw torque toward the front driveline when needed. Of course it "eats" some fuel mileage. So you don't want to run in it all the time as 2WD will give better gas mileage. But our CUT tractors have nothing like that.

Or a vehicle with AWD capability, just like Mitsubishi have been doing since the 90's with their Super Select 2 transfer case on the Mitsubishi Pajero/Montero and the L200 Pickup trucks.

Basically the transfer case has 4 positions: First - 2WD, Second - 4x4 with open center diff, Third - 4x4 with locked center diff and Forth- 4x4 Low Range with locked center diff. Some also had a Neutral position used for a mechanical front winch.

The 4x4 with open center diff can be engaged on the go as needed and it will disengage the front diff automatically in 2WD.

 

[LouNY]

Or you can get a transfercase like the RAM 1500's do and I wouldn't be surprised if many of the other vehicles with an auto mode and a loc mode do.
In the RAM half ton in the fancier trims the transfer case has Auto 4wd, Hi 2wd, Hi4wd and Lo4wd, the earlier models actually called it Auto 4wd and Hi lock 4wd and Lo Lock 4wd which was an out right lie.
Any of the RAM's with an Auto 4wd mode have a wet clutch setup in the transfer case going to the front axle. The vehicle computer decides how much of a voltage signal to send to the clutch depending on throttle position wheel speeds and steering angle as well as other inputs.
And it does this in both the Auto mode and the so called Lock mode. The fifth generations (new style 19's and up) do a much better job of "locking" then the earlier ones did.
My 15 was terrible, my wifes last 2 vehicles had a better awd system then my 4wd so called Lock, a Chevy Equinox and a little Jeep Compass.
I ended up with an aftermarket wiring harness that would feed the clutch full 12V+ with the flip of a switch which helped that truck a lot.
You could put that truck in 4 ho or 4lo lock and gently accellerating on ice just spin the rear tires the front would just grab a tiny bit every once in awhile. And it even had a limited slip differential in it.
The "19" that I have now actually bucks a bit in 2wd in a corner not much but a bit. When I got this "19" that was a check I did before I bought it as I had heard that it was a different and "improved" transfer case. I was thinking of a Chevy half ton till I learned that low range was an "option".
I still much prefer a solid mechanical transfer case.

 

[Farmer495]

Yes, unless you have a vehicle with a viscous coupling between front and rear driveline. Example Chevrolet Silverado of mine has an "Auto" setting on the 4WD selector. The idea is you can drive on a road that is dry is some places and maybe a little icy in others. You need 4WD one second and don't the next. It works pretty well, and prevents torque windup, but does throw torque toward the front driveline when needed. Of course it "eats" some fuel mileage. So you don't want to run in it all the time as 2WD will give better gas mileage. But our CUT tractors have nothing like that.

Yes, drove a few with that mode. My last truck with the transfer case on the floor was fun driving in the urban areas after snow storm, side streets not plowed, main streets plowed, moved that lever quite a bit going between dry pavement and snowpack, every turn seemed to be onto dry pavement!