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.