Auburn or Eaton posi?

[Cobra]

when i first started getting interested in cars i found this to be a very interesting read also has a cool animation that shows the difference in tire lines http://auto.howstuffworks.com/differential.htm

[LiftedAWDAstro]

So what you're saying is, in a corner, the front axle experiences a greater difference of RPM between the inner and outer wheel, than a rear axle would?

That is correct. The outside front tire rotates the greatest distance in feet and the inner rear tire travels the least distance.

[MountainManJoe]

I see, so where does the locker fit into it all? Does the rule apply to all locking, limited slip, and torsen type differentials? A gov-loc has an allowance of about 100 RPM between wheels before locking. Since the front axle turns quicker in turns than the rear, the transfer case must have a built-in tolerance as well.

[LiftedAWDAstro]

The locker will lock on any speed difference between the front tires and will not allow differential action.

Here is my experience:
Lynne had a 1987 Jeep Wrangler YJ. We flat towed it behind the SPB for wheeling. In the early years of the NP231J transfer case, when you put it into Neutral, the front and rear drive shafts were locked together. Well smarty me I figured I would install an Aussie locker (same as a Powertrax) in the front diff since the Dana 30 high pinion is stronger than the rear Dana 35 and it was less than $250. Installed it with ease and drove around the back yard. With it in 4WD, the inside front tire would tear the crap out of the yard on every turn. No big deal since it was a locker and I wanted the front locked.

Now comes the issue we are talking about. We decided we are heading to Paragon to do some wheeling. Throw the YJ into Neutral, unlock the steering wheel and hook up to the SPB. As I am pulling out of the driveway I hear tires squealing! WTF? Maybe I forgot to unlock the steering wheel. Nope, it was unlocked and the t-case and trans were in Neutral. So we headed down the road to only find the front tires would not steer due to the locker keeping it straight and not allowing differentiation. I had to remove the front drive shaft any time after that to flat tow the YJ. Once there was no torque to the front axle, the tires would differentiate and turn ok.

[MountainManJoe]

This is a bit confusing. Neutral sounds like it should allow the shafts to turn independantly, but what you describe sounds just like 4x4 mode.

Anyways, so the tearing up of your yard, and tire squeeling was caused by the axle locking and not differentiating. The exact same thing would happen if you put that locker on the rear, but to a lesser degree, since the rear traces a smaller arc in a turn.

[LiftedAWDAstro]

This is a bit confusing. Neutral sounds like it should allow the shafts to turn independantly, but what you describe sounds just like 4x4 mode.

These t-cases only did it in the early years. The later NP231J's do allow the front and rear shafts to turn independently of each other.

Anyways, so the tearing up of your yard, and tire squeeling was caused by the axle locking and not differentiating. The exact same thing would happen if you put that locker on the rear, but to a lesser degree, since the rear traces a smaller arc in a turn.

This is true and under torque the rear will lock. Just ask Zam.

[MountainManJoe]

OK I think I understand now... Front axles differentiate to a greater degree than rear axles, due to a greater turning radius. Most LS/lockers are designed for the amount differentiation a rear axle does, so putting it on a front would make it lock prematurely, and wear it out/break it.

But I still don't get why AWD should matter. The front driveshaft should turn the same way, locker or not.

[rlsllc]

Look at it like this: Lets say that you take a 90 degree turn around a pole. If you were on fresh snow, your tires would leave 4 tracks, the one closest to the pole would have travelled the least distance, and the track furtherst from the pole would have travelled the most distance. They all took the same amount of time to cover the distance, so as the tracks get further out from the pole, each wheel would have been travelling faster thn the one before.

The tracks should be, in order of closest to furthest, inside rear wheel, inside front wheel, outside rear wheel, and outside front wheel. The largest difference would be between the inside rear and outside front wheels, this is why the transfercase needs to differentiate on hard surfaces.

Also, having a front locker will make the front wheels want to turn the same speed, which will make them plow forward even when turned to the side, since they want to travel the same speed which means the same distance since the speed must differ in turns. There is a larger difference in wheel speed between inner and outer front wheels in a turn than inner and outer rear wheels. If I could find the image ( ) it would be obvious why. The three inner tracks stay fairly close to each other, but the outside front wheel track will be further from the rest in the sharpest part of the turn.

The longer the wheelbase, the more exagerated this effect will be. In a really short wheelbase vehicle (Jeep, Geo metro, etc) the tracks may even touch.

[MountainManJoe]

A gov-loc has an allowance of about 100 RPM between wheels before locking. Since the front axle turns quicker in turns than the rear, the transfer case must have a built-in tolerance as well...

... and I just found out what that is:

"The TCCM determines slip by reading prop-shaft speeds through a set of vehicle-speed sensors mounted on the transfer case. It makes continuous comparisons between the prop-shaft speeds and the vehicle road speed and decides by using a set of ratio comparisons how much duty cycle to apply to the clutch pack. At 0-10 mph a slip must be above 25 rpm before the TCCM takes action. The greater the road speed, the larger the amount of slip must be for the clutch pack to be applied."