Worth the risk? Is there a risk?

[HillbillyfromAL]

No it's like trying to explain lockers to your GF for the first time

Jeremy yes with it unlocked its effectively one wheel drive, and locked two.

Reading back over it maybe we mean the same things but have different ways of saying it. I think the argument here is over terms (vocabulary). For example you can't torque a loose nut, where I'm from. Therefore a wheel spinning in the air is delivering 0% of the torque that is being applied. I guess it also safe to say that its recieving 100% of the torque from the engine if the other three arent trying to move. So to stop any further arguments or confusion lets see if we can all agree on these two points.

1) Unlocked: The front and rear driveshafts can spin at different speeds. Power will go to the path of least resistance front to rear. Off-road ability is reduced

2) Locked: The front and rear driveshafts are forced to move at the same rate of speed. Power will go to both front and rear drive independent of resistance levels. Off-Road ability is enhanced

Would this explanation satisfy everyones definition of how it works?

 

[David Harris]

No it's like trying to explain lockers to your GF for the first time

I agree on this. . . :ylsmoke:

1) Unlocked: The front and rear driveshafts can spin at different speeds. Power will go to the path of least resistance front to rear. Off-road ability is reduced

2) Locked: The front and rear driveshafts are forced to move at the same rate of speed. Power will go to both front and rear drive independent of resistance levels. Off-Road ability is enhanced

Would this explanation satisfy everyones definition of how it works?

This isn't actually what's happening. Rather. . .

1.) Unlocked: The front and rear driveshafts can turn at different speeds. Torque is always split 50/50 to each axle, but the total torque is reduced to the amount on the side with the least traction if the two are not equal. Off-road ability is reduced.

2.) Locked: The front and rear driveshafts are forced to move at the same rate of speed. Torque can be applied to the side with the most traction if the two are not equal. Off-road ability is enhanced.

I think you are mistakenly relating the speed the shafts are turning with the torque that is being applied. An increase or equalization of the shaft speeds in itself has no effect on the way the system transfers torque. Does turning a bolt faster change the amount of torque it takes to turn the bolt? What matters is the amount of resistance, not speed. In this case the amount of friction between the wheel and the ground. An open diff allows the shafts to turn at different speeds, but its design has the unfortunate side effect of limiting the total torque applied to the amount on the side with the least traction. Locking the center diff eliminates the differential, thus eliminating the side effect of loss of traction. Limited slip or locking differentials were invented to solve this defect and regain traction in a differentiated system. The Range Rover's viscous coupling is an example of this in a center differential.

Traction control has the same net effect by applying the brake (or greater resistance) to a slipping wheel, thus allowing torque to transfer back to that wheel. The computer constantly applies the brakes at different wheels as traction changes. You can induce a similar effect on a vehicle with open diffs and no traction control by left foot braking when slippage occurs. This same technique works well with limited slip diffs like the trutrac as well.

Even in a completely locked system like an ARB or a spool, with one wheel in the air, the full torque will be applied to the wheel with traction, because that is the wheel with resistance. Same with axles: with the center diff locked, if you were going up a hill and the front axle came completely off the ground, nearly 100 percent of the torque would then travel through the back axle. Torque application only comes with resistance.

If you google "differential" you'll find plenty of other sites explaining this. It's a very commonly misunderstood topic on 4x4 sites. I used to think just like you do until it was pointed out to me (by Thom and others, in fact) and I confirmed it by researching further.

 

[overlander]

Since that question has been answered, back to the OP's topic. My wife has an 03' DII. I had a D1 prior to my 110. The 4.6 is dramatically more driveable than the 3.9 or 4.0. It's a dream to drive on long cross countries, and to me it seems the perfect power to weight ratio. We had the top end rebuilt proactively at 60k per factory recommendations and haven't had any issue with oil supply or such. the cooling system has a lot of pieces though, and it's recommended to make sure that everything is replaced proactively in the 80-90k range to avoid looming issues with leaks.

I was deployed when my wife bought it so I wasn't on hand at the time to advise her, but her 03 does NOT have the CDL. I told her to go at least 03 since that was first year of the 4.6, and at the time I could not have imagined that rover would have done away with the CDL when the hardware was right there. Top 5 Rover oops in my book. I guess they decided to bet the farm on traction control that year.. 04's have the CDL. I wouldn't even consider a DII without a CDL. that what makes the 04 so desireable. CDL and 4.6.

 

[HillbillyfromAL]

Even in a completely locked system like an ARB or a spool, with one wheel in the air, the full torque will be applied to the wheel with traction, because that is the wheel with resistance. Same with axles: with the center diff locked, if you were going up a hill and the front axle came completely off the ground, nearly 100 percent of the torque would then travel through the back axle. Torque application only comes with resistance.

This is exactly what I've been saying. A slipping wheel, or two doesn't deliver torque to the ground. As you said torque only comes from resistance. That's why when we brake a torque wrench out its only after the nut/bolt is tightened. How can an open differential deliver half of something equally if it doesn't apply the same to both sides? If your front drivers side tire is all that's spinning in the air, and the other 3 are sitting still then your open differential is now delivering all the torque and horse power made by the engine to that tire. The applied torque would be Zero, because there is no resistance. The same as if you grab a impact wrench and pull the trigger letting it spin in the air, it may produce 400ftlbs of torque but it doesn't apply any if there's no resistance.

Thats why I didn't mention torque in either my revised definitions, only power as in rotation, to get torque out of the equation.

 

[David Harris]

Thats why I didn't mention torque in either my revised definitions, only power as in rotation, to get torque out of the equation.

Power and torque are linked: horsepower = torque in ft. lbs x rpm / 5250. Which one you use makes no difference for how a differential works. Open diff = 50/50 split at all times. Locked = up to 100 percent can be applied to individual wheel/axle. How this works out depends on the traction available and the design of the diff.

The interesting thing is that a motor in a no load or light load situation, such as a vehicle motor without traction to the ground, is actually only producing power equal to its own internal friction and parasitic loss. That wheel spinning freely in the air is not getting the full power the engine can produce, even at full throttle, because it is not under a significant load. So, that impact wrench is not actually producing 400 lbs. if it is just spinning in the air, but rather only what it takes to spin the internals of the wrench. In physics this is called the principle of energy balance, or something like that. This link gives another explanation of this phenomenon:

http://www.madsci.org/posts/archives/1999-09/936762900.Eg.r.html

 

[HillbillyfromAL]

I take it back it's like arguing with a know it all GF that drives her daddy's Mercedes, carrying a little dog around in a purse.

 

[HillbillyfromAL]

Power and torque are linked: horsepower = torque in ft. lbs x rpm / 5250. Which one you use makes no difference for how a differential works. Open diff = 50/50 split at all times. Locked = up to 100 percent can be applied to individual wheel/axle. How this works out depends on the traction available and the design of the diff.

You really don't need to try physics apparently English and spelling were too hard for you to comprehend. Where did the "horsepower" come from? When the quote you quoted me on said " power as in rotation".