4 wheel drive question

[gerard]

Do a search on how a differential works. There are some pretty good explanations that show how a differential works. (There s areally good one that's about 50 years old that uses a spoked wheel to illustrate it, think it was by gm). Once you see how a differential works it becomes pretty clear.

 

[LD1]

I believe that they currently use electronic lockers (eLocker) that are only activated in Low range along with a part-time transfer case.

Thats kinda what I was thinking it could be, but if I owned one, I'd be figuring out how to control the lockers seperatly.

There are a lot of times lockers would be nice in 4H as well.

Or even 2H if you wanted to lay a nice patch of rubber out front. It would be nice to activate JUST the rear one.:thumbsup:

 

[Mace Canute]

In another thread (can't find it now), a gentleman said that he hadn't seen any differentials in any of the tractor front axles he had worked on which would make them just an angle drive. It would be easy enough to check on your own individual tractors.

 

[Heywood Jannockitov]

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.

I actually observed this first-hand last week when I had our Mule 610 jacked-up with the rear wheels off to check the brakes. My MIL thought they were dragging (they weren't). After reading about this "phenomenon" in another thread, I decided to do an experiment.

With the motor running slightly above idle, in gear and in 2wd with the rear tires off, I observed both drums turning forward slowly. I grabbed the brake drum on one side and held it motionless.

Sure enough, the drum on the other side sped up twice as fast. :thumbsup:

 

[pat32rf]

For those times when you are "hi-centered" with open differentials, sometimes gently applying the brakes will stop the airbourne wheel from spinning enough to transfer torque to the traction wheels.
A "locking" front dif could be a problem in a tractor because of the short wheelbase and sharper turns than you get in a truck or car. A "viscous" locker should work in the front but again even it could be troublesome in the rear on sharp turns....
Sounds like full time fwd (with aux locks) is the answer instead of the part time systems used in CUTs now

 

[LD1]

For those times when you are "hi-centered" with open differentials, sometimes gently applying the brakes will stop the airbourne wheel from spinning enough to transfer torque to the traction wheels.

That was common practice before rear diff locks became almost standard.

 

[k0ua]

For your viewing pleasure: YouTube - How Differential Gear works (BEST Tutorial)

This is the 1930's video. a little dated, but I think it is the best tutorial I have seen to explain the operation.

 

[SixHoeBob]

Can someone explain how differential steering works on a D8N Caterpillar?

I know, but it is too much bother to explain. Does anyone even care?

Just another example of a use for a differential.

 

[Raspy]

Four wheel drive systems in trucks (no transfer case differential and open axle differentials) are not two wheel drive! And two wheel drive trucks are not "one" wheel drive.

An open differential (no locker and no limited slip) ALWAYS applies equal torque to both wheels. If you get stuck and observe one front and one rear wheel spinning, it's because those two spinning wheels have the least traction, but both wheels on each axle are receiving the same torque. The wheels that are not spinning are applying the exact same torque to the ground.

An open differential means equal torque to both wheels, but unequal speed. A locked differential means always equal speed, but unequal torque. This is basic differential theory.

When someone applies the brake to help with a spinning tire on an open differential, they are adding friction, not only to the two rear wheels equally, but also to the front wheels. If anything, this will make it harder to move. Dune buggies often have a lever to apply the brakes to individual wheels. In this case you can add braking to the spinning wheel. This will add torque to the non-spinning wheel and help you move.

This idea that trucks are one wheel drive is an old myth that just won't die.

 

[Raspy]

For your viewing pleasure: YouTube - How Differential Gear works (BEST Tutorial)

This is the 1930's video. a little dated, but I think it is the best tutorial I have seen to explain the operation.

That's a great video. After all these years there is still so much misunderstanding of the simple differential. I can't count how many times I've heard the "one wheel drive" tale.

 

[LD1]

Four wheel drive systems in trucks (no transfer case differential and open axle differentials) are not two wheel drive! And two wheel drive trucks are not "one" wheel drive.

An open differential (no locker and no limited slip) ALWAYS applies equal torque to both wheels. If you get stuck and observe one front and one rear wheel spinning, it's because those two spinning wheels have the least traction, but both wheels on each axle are receiving the same torque. The wheels that are not spinning are applying the exact same torque to the ground.

An open differential means equal torque to both wheels, but unequal speed. A locked differential means always equal speed, but unequal torque. This is basic differential theory.

When someone applies the brake to help with a spinning tire on an open differential, they are adding friction, not only to the two rear wheels equally, but also to the front wheels. If anything, this will make it harder to move. Dune buggies often have a lever to apply the brakes to individual wheels. In this case you can add braking to the spinning wheel. This will add torque to the non-spinning wheel and help you move.

This idea that trucks are one wheel drive is an old myth that just won't die.

Call it whatever you want.

But when you are stuck, and only one wheel on each axle is slinging the mud......

I personally dont care what people call it. And I often call it one wheel drive myself. Becasue when you are stuck, and one wheel is spinning like on ice, that is next to NO torque. So the opposite wheel is also applying next to NO torque.

When I think in terms of TRUE 2wd or TRUE 4wd, I think of BOTH wheels being mechanically bound to turn the same speed. IE: LS, locker, spool, whatever. That is TRUE 4wd.

The reason I differientiate between them is because if ALL 4wd trucks were , as you call it, 4wd: That sounds the same. And when you are stuck, there is most definatally a difference. And since you can't call a 4wd with lockers a 6wd or 8wd, that demotes the 4wd with open diffs down to a 3wd or 2wd.

And in all reality, most people that refer to it in these terms do indeed know how a differential works. THATS why they call them 2wd's. Most city slickers that I know or have talked to thought didn't know that their truck only spins 2 wheels when stuck.

 

[Mace Canute]

Raspy, you can lead a horse to water, etc, etc, eh? Sometimes it's like trying to explain the earth is a sphere to flat-worlders.

 

[Raspy]

Call it whatever you want.


And in all reality, most people that refer to it in these terms do indeed know how a differential works. THATS why they call them 2wd's. Most city slickers that I know or have talked to thought didn't know that their truck only spins 2 wheels when stuck.

Well, if they have for wheel drive, they might spin two, they might spin three and they might spin four. It's incorrect to simply say they will "only spin two". But the wheels on each axle will be getting equal torque if equipped with open differentials. In other words, all four wheels get torque, or, four wheel drive. Traction is limited by the one with the least traction on each axle. Seems simple enough, and really has nothing to do with how fast a wheel is turning. A spinning wheel does not mean that that wheel is the only one getting power.

Say it any way you wish, but they are all getting power and they are almost never turning at the same speed, regardless of the conditions. If you oversimplify it and say it's really two wheel drive (when it's not), you promote the same old myth and just add more confusion to those that don't understand the system.

 

[Gobblin Tom]

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

Sorry, I should have been more specific, the only factory vehicle I know of that has lockers is the jeep rubicon. I believe they are air lockers that you are able to engage both the back wheels and both the front at the same time or one or the other. I know that you can do some "Other" work to make it possible to use this in high range also. If you have all 4 engaged even in gravel be prepared for a bouncy ride! My chevy truck now has a limited slip in the rear end so it will only run at the most 3 wheels. So I guess I should call it a 3wd!!!!

 

[LD1]

The newer dodge "power wagon" uses e-lockers as well as a electronic disconnecting front sway bar.

And I think maybe the new Ford SVT raptor has e-lockers as well.

 

[Raspy]

My chevy truck now has a limited slip in the rear end so it will only run at the most 3 wheels. So I guess I should call it a 3wd!!!!

Did you take one wheel off? Did you disconnect one wheel from the power train? Which "three" does it "run".

Not meaning to be difficult here, just wondering if you get that they are receiving equal torque and unequal speed with an open differential and unequal torque but equal speed, with a locked diff.

 

[SPYDERLK]

Call it whatever you want.

But when you are stuck, and only one wheel on each axle is slinging the mud......

I personally dont care what people call it. And I often call it one wheel drive myself. Becasue when you are stuck, and one wheel is spinning like on ice, that is next to NO torque. So the opposite wheel is also applying next to NO torque.

OK then ... NO wheel drive.
larry

 

[LD1]

OK then ... NO wheel drive.
larry

That is a good way to put it.

I guess it all depends on how you define "drive".

Because if you are "stuck", it dont matter how many wheels are a spinning, you ain't driving nowhere:laughing::laughing::laughing:

But really, I understand the point you are making raspy. And I agree with you. All I am saying is that I personally dont care what people call it. I understand what they are saying. And if I have to use these "improper" terms every once in awhile to explain something to someone, then so be it.

 

[TripleR]

That is a good way to put it.

I guess it all depends on how you define "drive".

Because if you are "stuck", it dont matter how many wheels are a spinning, you ain't driving nowhere:laughing::laughing::laughing:

But really, I understand the point you are making raspy. And I agree with you. All I am saying is that I personally dont care what people call it. I understand what they are saying. And if I have to use these "improper" terms every once in awhile to explain something to someone, then so be it.

But wouldn't it be better to try to educate them? I know I sure appreciate the better understanding I now have due to the posts and examples given by other posters.

 

[ovrszd]

I love threads like these. I Jeep. I hardcore Jeep. I have a complete understanding of differentials, lockers, limit slips, etc.

I find that those who get caught up in "word perfect" terminology tend to have the least amount of practical application under their belt.

When you are stuck in 4wd and open diffs and are walking for help because you are spinning only two tires and not moving, you can think of plenty of things to "call" it.