Tractor Sizing How important is rear diff lock on CUT?

[The Suburban Farmer]

The differential lock saved me this weekend. Despite knowing it was too muddy, I just couldn't resist the urge to get out the tractor since the sun was finally shining, and thought I'd move some of the firewood that we cut last year but never moved to the wood shed. I did get stuck trying to get back up a small hill and my tire dug a rut before I even knew it happened. Differential lock was all I needed, and once both tires had traction, off I went. It's funny, but when I felt my tire slip the first time I IMMEDIATELY thought about this thread.

 

[LD1]

LD1, I had a "knocking your head on the keyboard" icon for this type of case. I gotta try to find it.
larry

The one into the brick wall works :mur:

 

[jwayne14]

If you got 2wd and no diff lock, you only have 1wd
If you got 4wd and no diff lock, you only have 2wd

I use my diff lock most when moving dirt/gravel. Helps me push deeper into pile.

you still have two wheel drive. ld1 is right about that.
however, ld1, when one tire is spinning and the other isn't, the non spinning tire cannot be receiving the same torque as the spinning one. that would be effectively locked. if the non spinning tire was receiving the same torque, the spinning tire would never have started spinning.
in spinning, the tire has lost its resistance (to the ground). so the torque follows the path of least resistance. and, youre stuck.
in braking the spinning tire with its brake only, you are fooling the rear end into thinking the tire has regained its resistance. (it has, actually. just with the brake shoes and not with the ground). but the rear end doesn't know the difference. so it begins to equal out the torque delivered. ie, it now gives torque to the non spinning tire. this is shown by slightly braking the spinning tire; the tractor eases off. lock, or nearly lock, the spinning tire with its brake; the tractor moves away more suddenly, because more torque was transferred.

when equal resistance (grip) is felt on the tires, equal torque is given to each tire. 2 wheel drive, c4ranch.
imo, split brakes are much more usable than a diff lock. sort of an adjustable diff lock. except, of course, for the power loss caused by braking.

 

[jwayne14]

To each his own. I still maintain that if traction is similar (and barring unusual circumstances it usually is close) that the locker don't add much help when pushing a pile.

yes, I have to agree. if traction is equal, I don't see how a diff lock can do anything extra.

 

[LD1]

Wrong. The torque is equal even if one wheel is spinning. You are still applying the same torque to the non spinning tire.

You can apply torque but not have movement.

When braking the spinning tire, it takes more torque to spin it. Since torque is split equally, that means more torque goes to the non spinning tire that has better traction. And hopefully get you out of the mud.

Open diff is equal torque and unequal speed

Locker is equal speed, unequal torque

 

[jwayne14]

Wrong. The torque is equal even if one wheel is spinning. You are still applying the same torque to the non spinning tire.

You can apply torque but not have movement.

When braking the spinning tire, it takes more torque to spin it. Since torque is split equally, that means more torque goes to the non spinning tire that has better traction. And hopefully get you out of the mud.

Open diff is equal torque and unequal speed

Locker is equal speed, unequal torque

if it were equal torque all the time, then never would only one tire spin.
they would both spin. this is not the case.

I see what you mean, though. the overall torque is only what the spinning tire can use? which isn't much if its spinning.
maybe it is always equal. Ive always looked at it as not.
when braking the spinning tire, you put the resistance back. that's for sure. so what youre saying is the overall torque then goes back up equally? sufficient now to move the vehicle with the good tire?
with a hard brake on the spinning wheel, perhaps youre not so much transferring more, as you are increasing it more (vs a light brake pedal) overall?
makes sense that way too.

a diff lock should always tear grass with the inside tire. a well practiced split brake application will not.

 

[C4Ranch]

No worries fellas. When you climb out of your tractor simulators I'll buy ya a beer.

Not sure I've ever had any real experience where traction is equal. One tire always seems to spin before the other. This equal traction sounds more in theory than real life. If ya got the engine turning only 1 wheel, that's 1wd in my book. But you can debate all u want.

More people on this thread seem to know the value of a locker from experience.

Flame on.

 

[LD1]

If one tire is on ice and one on dry pavement, it takes less torque to spin the tire on ice.

Let's say it takes 50 ft lbs to move the tractor. But only 25 to spin the tire on ice. BOTH tires will see 25 ft lbs, but only one will spin, and the tractor won't move.

Apply the brake now to the tire on ice. It now takes 75 ft lbs to spin it. In turn, the other tire will also see 75 and the tractor will move.

You are forgetting, you don't need movement (spinning tire) to have torque. The non moving tire does get the same torque as the spinning one.

 

[SPYDERLK]

if it were equal torque all the time, then never would only one tire spin.
they would both spin. this is not the case.

Torque. Traction. Think a little more.
,,,larry

 

[McREBEL]

While it is true the torque in an open differential is always equally distributed the thing to keep in mind is the torque delivered is limited to the amount that will not make the tires slip. If one tire is up in the air it takes very little torque to make it spin; therefore, very little torque is being applied to the non-spinning wheel also. Equal torque to each wheel, but very little torque. Hence, you aren't going to get much forward movement. When neither tire loses traction then you get the maximum torque the drive train is capable of producing.