Four wheel drive is not really four wheel drive?

[edrobyn]

Got my 4 wheel drive tractor a few weeks ago and was mowing on a small slope going forward and tried to back up in some wet grass and got stuck. I was in 2 wheel drive and the left rear was spinning so I put it in four wheel drive then the left rear and right front started spinning. So I locked the rears and got unstuck. I would have thought that when the front starts to spin an antispin differential would kick in and the other front wheel would try to grab. It dawned on me that the fronts don't lock so basically the most I can get is a 3 wheel drive. Am I missing something here?

 

[BethesdaEC]

You are correct, the front is a standard differential with no lock.

 

[jinman]

Am I missing something here?

No, the same as saying 2WD when referring to an auto. It's really 1wd if you get into ice or mud.

BTW: A poor man's differential lock is using differential brakes. On old 2WD tractors without diff-lock, we used to apply the brakes to the spinning wheel to force the wheel with the most traction to pull. It works well, but you can't do that to the front wheels. Also, someone pointed out to me recently that even though you have only 3wd when driving forward, when you brake, you have full 4 wheel brakes because if the driveline to the front differential is locked, one wheel can't turn (unless the other wheel turns backwards).

 

[art]

On compacts it's normal that the front doesn't have limited slip till you get to the larger tractors.
We have often been reminded of the three wheel drive at best when in slippery conditions.

 

[SPYDERLK]

On a standard [open] differential it may seem that only one wheel drives. But actually both do. Its just that you only get twice the thrust that the wheel with the lesser traction can provide. If that wheel has almost no traction ... well, twice that isnt much.
larry

 

[slowzuki]

Was going to say exactly what spyderlk said. Practically speaking, I've got a large MF with front and rear diff lock. These aren't hard numbers but using 4wd, 4 wheel lock as the 100% traction reference while pulling something, unlocking the front diff barely makes a difference. Unlocking the rear might knock you back to 85%, putting in 2wd gets you back to about 60%.

Using the front loader, or backing out of somewhere pointed downhill you were sinking into is a whole different story. The front unlocked might knock you back to 80%, rear unlocked, 70%, 2wd 20%.

 

[TripleR]

There is another thread on this; very long and very informative. It explains SPYDERLK and slowzuki are talking about.

 

[edrobyn]

Thanks I'll try to find it.

 

[Mark Page]

I've found the same thing to be true with pick ups. I've owned Ford, Dodge and Toyota. I've never been able to get more that 3 wheels engaged. Very frustrating when you get hung up.

 

[edrobyn]

I wonder if the old 4 wheel drive trucks where you used to have to get out and lock the hubs were true 4 wheel drives.