4 wheel drive question

[new jersey mike]

If a tractor with 4 wheel drive engaged is really only driving 3 wheels? Would you have to depress the differential rear lock for all 4 tires to be engaged?

This is just a saturday morning coffee thought..

 

[fredhargis]

On my Kubota it seems like with 4WD engaged it's actually only 2 wheel drive (one on each axle). Then, when I hit the diff lock I get 3 WD.

 

[Egon]

A normal four wheel drive tractor is only two wheel drive. One front tire and one rear tire may have traction and be moving the tractor.

With the differential lock engaged both rear wheels as well as one front wheel may have traction and be driving the tractor.

 

[TripleR]

Well, as long as traction is equal, you have a four wheel drive. Someone put a pretty good explanation on this up at one time, maybe they will re-post.

Our M8540 has differential lock and limited slip front differential, so on some you can have power to all four wheels in different traction situations.

 

[new jersey mike]

Your kidding me!! only 1 in the front and 1 in the back. I need to read more. I really thought it was like a 4x4 truck, I guess not so much.

Is it a safety issue because of the traction and torque issues?

 

[nue2farm]

Don't want to burst your bubble, NJ Mike, but 4x4 trucks only drive two wheels in 4x4 mode. To have true 4x4 drive you must have "lockers" front and rear. Have fun and stay safe....

 

[k0ua]

Your kidding me!! only 1 in the front and 1 in the back. I need to read more. I really thought it was like a 4x4 truck, I guess not so much.

Is it a safety issue because of the traction and torque issues?

Well I have some bad news for you. Four wheel drive trucks are only 2 wheel drive also. Unless the truck is equipped with some type of limited slip, or locker, in certain situations only 2 wheels will have power. To prove this to yourself, cross a ditch at an angle, and get the truck in the position of having one front wheel and one rear wheel with no contact with the ground, then make sure your vehicle is in 4 wheel drive. If your vehicle is not equipped with limited slip, or locker, you will spin the two wheels that have no contact with the ground, and the two wheels that are firmly on the ground will have no power applied to them. This is the way most CUT's work also. Of course you can split-brake the one rear spinning wheel, or engage the differential lock to get moving. In this case 3 wheels will have power. You may have always owned 4 wheel drive vehicles with limited slip in the rear differential and not noticed this, but millions have been built without any form of limited slip, and will act in this way.

James K0UA

 

[new jersey mike]

As Joe Pesci would say ok ok ok

So lets see in theory if I am going down a steep hill in 2 wheel, low gear and using the engine torque to slow me IF the 1 rear wheel looses traction would the tractor start to free-wheel until the rear dug in again?

 

[k0ua]

As Joe Pesci would say ok ok ok

So lets see in theory if I am going down a steep hill in 2 wheel, low gear and using the engine torque to slow me IF the 1 rear wheel looses traction would the tractor start to free-wheel until the rear dug in again?

Step one: don't go down a steep gravel over pavement hill with a heavily loaded bucket in a low gear in 2 wheel drive. What happens is the rear tires will start to slip and they will not regain traction until you get to the bottom. Do not ask how I know this. In my case, both tires lost traction at the same time, I suppose if one tire had good traction and one slipped, the tractor would try to skew sideways a bit, but the front tires would probably prevent this until the other tire lost traction also. If you are in 4 wheel drive the front tires will provide some engine braking action through the driveline connection. I can tell this to you as a fact. Some here discount this notion, but I have personal experience.:laughing:

James K0UA

 

[Gary Fowler]

Let me tell you guys my take on this from having several times gotten stuck with only 2 wheels on the ground. Indeed if you cross say a deep ditch on an angle that your frame limit puts 2 of the 4 wheels off the ground, you will indeed stop moving and the two wheels in the air will just spin along with absolutely no power to the other two. Differential lock will normally cure this situation an push you on thru. Now in a different scenario, you are pushing your FEL into a pile of dirt and are geared low enough that the engine isnt going to stall. If you get to much resistance and start spinning the tires, you dont get 2 holes in the ground, you get 4 holes. All four tires will continue to spin at the same rate till you dig down and get high centered if you dont stop. The tractors are like cars and trucks with limited slip differential. If all the tires have equal or near equal traction they will all spin and provide traction. Just like a car can burn rubber and leave a double strip of it on asphalt, but put one wheel of that same car on a watermelon rind and you are stuck.

 

[k0ua]

Let me tell you guys my take on this from having several times gotten stuck with only 2 wheels on the ground. Indeed if you cross say a deep ditch on an angle that your frame limit puts 2 of the 4 wheels off the ground, you will indeed stop moving and the two wheels in the air will just spin along with absolutely no power to the other two. Differential lock will normally cure this situation an push you on thru. Now in a different scenario, you are pushing your FEL into a pile of dirt and are geared low enough that the engine isnt going to stall. If you get to much resistance and start spinning the tires, you dont get 2 holes in the ground, you get 4 holes. All four tires will continue to spin at the same rate till you dig down and get high centered if you dont stop. The tractors are like cars and trucks with limited slip differential. If all the tires have equal or near equal traction they will all spin and provide traction. Just like a car can burn rubber and leave a double strip of it on asphalt, but put one wheel of that same car on a watermelon rind and you are stuck.

+1,:thumbsup: If traction is equal, all 4 wheels apply power to the ground, but if traction is un-equal, then only 2 in 4 wheel drive or only 1 in 2 wheel drive, unless there is a limited slip mechanism or mechanical differential lock.

James K0UA

 

[bigbull338]

a 4 x4 can pull in varies combos,such as the front wheels pulling,or the back wheels pulling.or 1 on each side pulling.also a 4x4 can stay on top of the mudd better.the wider tires you have the better you can stay on top,as it spreads the weight of the tractor out.

 

[The Haymaker]

A normal four wheel drive tractor is only two wheel drive. One front tire and one rear tire may have traction and be moving the tractor.

With the differential lock engaged both rear wheels as well as one front wheel may have traction and be driving the tractor.

ALL 4 wheels will drive. Under enough load the tire with least amount of traction (friction) will slip.

This sounds like the old "one wheel drive" wives tale I have heard many tell. Too many don't understand how a differential works.

On the differential lock, am I the only one who thinks the normal setup on a CUT is cheesy and the industry could do better?

 

[TripleR]

ALL 4 wheels will drive. Under enough load the tire with least amount of traction (friction) will slip.

This sounds like the old "one wheel drive" wives tale I have heard many tell. Too many don't understand how a differential works.

On the differential lock, am I the only one who thinks the normal setup on a CUT is cheesy and the industry could do better?

No, there are at least two of us. Also put me down for wondering why windshield wipers having gotten any better.

 

[Gobblin Tom]

The only modern vehicle that I know of with true 4wd is the Jeep Rubicon. The only way it will work to drive all 4 wheels is in low lock. I had one for a while and it was a blast going over rocks etc. as far as the tractors go and the money you pay it is amazing that they don't have a true 4wd or some kind of locker for the front like the rear.

 

[Gene :^)]

As Joe Pesci would say ok ok ok

So lets see in theory if I am going down a steep hill in 2 wheel, low gear and using the engine torque to slow me IF the 1 rear wheel looses traction would the tractor start to free-wheel until the rear dug in again?

TRUE - In fact, if one rear tire starts slipping and the other holds on... the slipping tire will start spinning backwards as you go down the hill. Oh, and you will speed up proportional to the amount of slip.

My tractor only has rear wheel brakes, so I never go down hills without 4wd engaged. Especially if I have a load in the FEL which makes the rear tires lighter.

Gene :^)

 

[The Haymaker]

No, there are at least two of us. Also put me down for wondering why windshield wipers having gotten any better.

George Bush?

I curse the day when the flat windshields of the older Navistar 9000 series trucks were replaced with less spartan curved ones. I have not seen in a snowstorm since, hundreds of mailboxes can attest.

Anyway, back on topic. New Holland has the limited slip clutches in the front driveshafts to allow full time 4wd. I loved it. Why not go one step further and go with limited slips diffs?

 

[JoelD]

I guess one obvious problem with 4wheel lock is the propensity to tear up diffs or axles or transfer cases if you turn the wheel under load with good traction.

Joel

 

[LD1]

The only modern vehicle that I know of with true 4wd is the Jeep Rubicon. The only way it will work to drive all 4 wheels is in low lock.

I am not saying you are wrong, because I know absolutly NOTHING about a Jeep Rubicon, But how exactally is this possible???

The difference between TRUE 4wd and the one-wheel-peel is in the differentials NOT the transfer case. So how does putting it in 4L suddenly make open differential axles become lockers???

And since we are talking about how differentials work, so far, most of the descriptions have been SPOT-ON.

But I will add one thing. When you are stuck, whether it be tractor or truck, and you are one-wheel-peeling at the axle.....The tire that IS spinning is doing so at twice the normal rate. IE: if you are stuck in your truck with one wheel on ice and the other on pavement, and your spedometer registers 40MPH, the one wheel that IS spinning is doing 80MPH.

And as a result, all the little spider gears in the open carrier (which normally dont spin if going straight and only spin a little when turning) are spinning extremely fast. I have seen this cause the spiders to gald and weld themselves to the diff pin creating a locker. Until the next time you turn, then kaboom:confused2:

 

[Egon]

ALL 4 wheels will drive. Under enough load the tire with least amount of traction (friction) will slip.

This sounds like the old "one wheel drive" wives tale I have heard many tell. Too many don't understand how a differential works.

There are also many of us who do understand how a differential works and have actually seen the internals in action.

I can remember a day back in 1963 when the Land rover I was driving crossed a sharp v trench and the sat there with one wheel on each end up in the air and turning but not achieving any forward or rearward thrust. Engaging four wheel low, setting the throttle, stepping outside and rocking the vehicle with my hands resulted in both wheels on one side occasionally grabbing sufficiently to eventually moving the vehicle across the trench and on to the desired trail I wished to follow.

Would this action be an indication that the mysterious ways of a differential were known to me?