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.

 

[slowzuki]

All the grenaded ones I have seen are in 1/2 axles. Case split in two. Not heard of much trouble in larger axles.

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.
James K0UA

 

[slowzuki]

Egon has it, visualize the twist being applied to the axle shafts. You're not going to break the one with the tire in the air, its just along for the ride, nearly no torque on it. All the torque is being transmitted via the one contacting the ground.

With a locked diff, the only time the torque is equal, is if both tires have the same traction, and you're going in a straight line vs in an open diff its always (for simplicity sake) a 50-50 split limited by the tire with the least traction.

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

 

[JoelD]

I understand the point
The torque is a result of the traction no traction no torque in my locker question
Joel

 

[JoelD]

This post also explain why my tractor goes twice as fast when I apply split brake when plowing the driveway

 

[Raspy]

Every locking diff or limited slip diff is a compromise.

Ones that lock completely with air or electrically are either in or out. This can cause a lot of binding, but works well off road, slow speed or to get you out of a mud hole. Then it has to be turned off to prevent binding on high traction surfaces. The gov-lock allows spinning up to a certain RPM and then bang, it locks. I had one in a Blazer and it seemed to be a hindrance in off roading because of it's sudden locking, then unlocking and allowance of slipping, but it's good if stuck temporarily in the mud. My Dodge AAM axle has a very mild system that is pretty much invisible, but slips a lot. My older Dodge Cummins, with a Dana system, I think called Trac-Loc, was a clutch system that was invisible but locked completely to where one wheel could be off the ground and it would spin the one on pavement. Very, very good. The all gear Gleason might be the best ever invented. It can't spin up one wheel and is all gears, but it's hard to manufacture and expensive. The AAM system is similar, but cheaper. The limited slip units with clutch plates behind the spider gears that try to lock by using the expanding force of the spider gears only apply a small amount of torque to the stationary wheel and can't "lock".

In the long run, for many modern drivers, the traction control system that applies the brake on the spinning wheel, might be the best compromise. Invisible, powerful, immediate, silent. It is good on snowy highways, but probably not for hard core wheeling.

The mechanical systems can get you into trouble on a side hill. Without a locker you just spin the uphill wheel and can't proceed. But with lockers, one end or both will lock and you slide sideways. My Samurai can get into trouble like this. But, overall I love LS diffs and always have them in my trucks. With good driving I can always get much farther with them.

 

[SPYDERLK]

Then the solution from someone else: "well, my Daddy used to just step on the brake when he spun a wheel and just drive right out".

The reason that is effective is twofold; 1] Daddy had drum brakes. These are leading shoe and therefore self energizing ... the brake on the spinning wheel is augmented by this effect, 2] as that brake warms from slipping its friction coefficient increases, thereby further increasing the braking effect on that wheel compared to the other.
larry

 

[Don87]

The reason that is effective is twofold; 1] Daddy had drum brakes. These are leading shoe and therefore self energizing ... the brake on the spinning wheel is augmented by this effect, 2] as that brake warms from slipping its friction coefficient increases, thereby further increasing the braking effect on that wheel compared to the other.
larry

Maybe you read Raspy's original post wrong, or maybe I read yours wrong.................I think i'll drink a beer or three and re-read the posts.