4 wheel drive question

[slowzuki]

Yes, it can only deliver approximately twice the torque of the tire with the least traction.

I understand what you guys are saying and You are right, I guess My point is that in a open diff it depends on resistance from the other side to provide full torque to both axles.

 

[Raspy]

I understand what you guys are saying and You are right, I guess My point is that in a open diff it depends on resistance from the other side to provide full torque to both axles.

This was stated way back earlier in this thread.

In an open diff, the torque getting to the wheels is limited by the wheel with the least traction. Or, more precisely, the tire with the least resistance to turning. So a brake applied to the slipping wheel will add torque to the non slipping wheel, as is the case on tractors with individual rear brake pedals.

And remember, torque is a force, not a speed. It's not dependent on movement. Think of a torque wrench on a bolt. When the bolt gets to the required torque it stops turning, but the force is still being applied. Same with a stuck tire. It is receiving the same torque as the spinning tire, with an open diff, but the torque is limited to what is required to spin the slipping tire.

 

[JoeL4330]

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!!!!

My 2008 Jeep Grand Cherokee w. Quadradrive II has electronic locking diffs front and rear and they work all the time, Hi or Lo range...I notice that the 2012 models will not have an electronic locking diff in the front.

 

[JoelD]

Sorry I'm still stuck on different torque to the two wheels when looked

To me locked means locked and therefore torque transmitted to the wheels would be the same?

I'm missing something basic I think

Joel

 

[Egon]

To me locked means locked and therefore torque transmitted to the wheels would be the same? /QUOTE]

With a locked differential if each wheel sees equal resistance to turning the torque will be the same.

Now, with one wheel in the air the other wheel doing the driving it's obvious the driving wheel will require more torque to turn it. The air wheel requires very little force to turn it.

Both wheels will be turning at the same speed.

 

[JoelD]

I understand I'm thinking the wheel under load will consume more of the available torque

Joel

 

[284 International]

JoelD, no single wheel can see more torque than the net output torque of the engine multiplied by the range box, transmission, and rear end gears. I think part of the difficulty may come in how you're choosing to look at it, or the frame of reference.

Try from the tire side: No tire can push more than how much grip it has (coefficient of friction) combined with how much weight is on it. Those two things tell us how much traction is available to push the vehicle forward. If you have one tire on a slippery surface, or in the air, the available torque it has is very zero. As a result, when power is applied, it spins, and the tire on the ground sees a torque from the driveshaft equal (Oversimplified, but close enough for us at the moment) to how much force it takes to freely spin that loose tire.

Because of the spider gears, it will also turn twice as fast as the ring gear. (This is where Slowzuki's part of seeing double the torque comes into play, but ignore it for the moment, because we're assuming there is zero resistance to turning.)

If you press on the differential lock, both tires will now spin at the same RPM. However, the tire hanging in the air still has zero traction, so it takes no torque to make it rotate. (Again, ignoring rotational inertia and bearing friction and so forth) That hanging tire also contributes nothing to pushing the vehicle forward; there is nothing for it to push against, so that makes sense. The only tire that is pushing, then, is the one on the ground, and it will see, through the axle shaft and wheel, whatever torque is required mathematically to push the machine forward. (Again ignoring inertia)

Basically, the only torque that is measured through the shafts and wheels is force applied against something. If you have a torque wrench set to 150 ft-lbs, and you pull on it super hard, but the bolt isn't snug yet, the bolt doesn't see 150 ft-lbs. As it begins to draw snug, and get tougher to turn, pressing the pieces together, it will see increasing torque up to 150 ft-lbs. When it's loose, the bolt sees basically zero torque. You can't apply 150 ft-lbs to a bolt until you're pushing against something.

The tires or axles, in our oversimplification, can't transmit any torque unless they are pushing against something, too. :thumbsup:

 

[284 International]

Oops. Egon just said in 4 lines what I had to do paragraphs about. Nicely put, sorry for the lengthy post.

 

[k0ua]

I wonder if anyone would care to comment about my Eaton G80 "gov-lock" locking rear differential I have in my 2010 Silverado. I have heard good and bad about them. The good is they work well, and don't cause any problems when you "go around the corner" no clunking , no slipping no scubbing, because the clutch disc's are not locked until there is a difference of speed between the axles of either 25 or 100 rpm. I have heard both numbers. There is a small govenor mechanism with "fly-weights" that fly out and engage the clutch packs at some difference speed. (25 or 100). The bad I have heard is they can and do "grenade" and you wind up with about 50 "pieces parts". I have seen photo's of a couple of them and one video on you-tube of a guy destroying one. But he was an idiot, and giving the truck all sorts of h3ll by turning sharply under full throttle, to slide the rear of the truck around. He did this for at least 5 minutes until there was a loud bang and the "gov-lock" gave up. I try to be gentle with it, and when spinning start with one tire, you can feel it lock up with a small clunk and you are moving. Now it may last me forever if I continue to use it as intended and not make an effort to destroy it. Or, maybe not. What say you?. Now also the truck has electronic traction lock, which will brake the spinning wheel, and reduce throttle response. Does anyone know if this works with the front axle's also.? I know the 'gov-lock" is only in the rear diffy, of course. but if the electronic traction control works on the front( and I think it does) that should be a good thing. Now all of this said, if the traction control, is effective, why have the Eaton G80 locking differential at all? Why have 2 systems at the same time? I will say this: I have never been stuck in this truck. and when wheel spin starts one or both systems kick in, and you are stuck no more, and this is usually in 2WD. Comments welcome

James K0UA

 

[reichebrown]

I put a chain on one front tire to help with steering on my 2305. There were several times this winter when I had the did lock on that all the only wheel bot spinning was the one with the chain on it.