Mysterious 4wd problem

Makes sense. It can be difficult to get the fork perfectly lined up with the slot in the collar, because your depth perception is off when installing. I have a similar disconnect on my old Jeep and while I have all the access in the world to the front axle to give it my best shot, it's still difficult to be sure the fork actually engaged the collar properly.

Good deal that its fixed now.

 

With the tires in the air, I see turning my front driver side tire spins the front driveshaft in 2WD. Is this normal? I’m finding conflicting information on TW and the internet.

 

Certainly can depending on how much drag there is in the diff, you said you have a locker in it too so that's gonna affect things.

 

Typically no that is not normal, the left axle spinning forward should be spinning the intermediate axle piece backwards instead of spinning the driveshaft. The driveshaft is pretty heavy and that intermediate axle is very easy to turn, so my guess is you’re still locked in at the ADD somehow, and the resistance of the right side is forcing the left side to turn the driveshaft instead.

Have somebody turn the right tire forward instead and see what happens.

Edit: ahh, if you have a locker then yeah that’s pretty typical. They usually have plenty of resistance in them and will spin the front driveshaft instead of the ADD. If I had a locker, I would delete the ADD because there is no point in having it anymore.

 

Driver side is definitely locked to the front driveshaft in 2WD. Passenger side tire spins freely.

Is this true for a selectable locker as well?

Mine is an autolocker, which is nominally “open” when the torque from the tires rolling exceeds the torque from the driveshaft, as I understand it.

 

ADD is working fine if passenger wheel rolls freely.

Even if the locker acts as an open diff, most of them don’t have internals that truly spin freely, so the left axle turning ends up rolling the diff forward and spins the driveshaft. The difference is that with the diff rolling forward, that means the intermediate shaft is also rolling forward. Which is not a problem, that just means that the ADD is essentially doing nothing at all now, because all of the parts are spinning anyways.

 

Depends on the type of locker, clutch type lockers commonly have enough friction that they won't let the diff free-spin.
Not gona hurt anything other than a slight hit to fuel economy since you have more rotating mass.

 

A few things are interesting about this:

First, my turning radius while coasting in 4wd (with locker nominally “open”) will be tighter in one direction, since the front tire that is locked to the transfer case will always be the driver side, instead of being able to modulate to the passenger side when it requires less torque to spin.

Second, my notion of making the front actuator cable operated, in order to disengage it to achieve 2lo, will not work, because the driveshaft will always be turning the driver side wheel.

Third, if my ADD ever becomes disabled in the open position, I will still be able to achieve 3 wheel drive.

That last point has implications for breaking a CV axle in the field. As long as I put the good CV on the driver side, I can limp back to civilization in 3 wheel drive with an unplugged open ADD.

I’m tempted to keep my ADD just for that contingency.

 

No, that’s not really how it works. The diff has enough resistance to spin the driveshaft. But that is low torque. As soon as you actually applied power to the diff via the driveshaft, you’re going to spin the diff and go nowhere, because all the power would go out the disconnected right side.

in 4wd, your turning radius will suck no matter what because of the ADD engaging and making the system too tight to turn sharp without binding.

The cable would work fine for 2Lo, because of the torque from the driveshaft spinning out the disconnected right side.

no, broken add would result in no torque to get you anywhere. You’ll be in 2wd.

 

I think I have verified at this point the ADD does not disconnect the driver side from front driveshaft. If the TC is in 4, it will always power the driver side tire, even with the ADD in the 2WD position. I will re-test this to make sure. (That would prohibit achieving 2lo simply by moving the ADD to 2WD.)

As soon as I apply power to the diff via the driveshaft, it locks and delivers full power to both sides. It’s an autolocker. Even if the ADD is allowing the passenger side to spin freely, it will still send full power to the driver side.

Turning in 4wd may always suck, but *while coasting* — that is, when an autolocker is nominally open — it theoretically will suck more in one direction than the other if the driveshaft cannot modulate engagement from one front tire to the other as with a truly open diff. This is easy enough to test.

 

Edited my above post for clarity.

To explain the turning radius issue more specifically, consider a coasting downhill sharp turn. In a truck in 4WD with truly open differentials, the transfer case will force one rear tire and the one front tire to turn at the same speed. But the two tires have different turning radii; hence the suck.

But on my truck, the front driveshaft seems linked to the left front tire at all times. So it will force one rear tire to always turn at the same speed as the left front tire.

The turning radii in that case will either be even more different from each other, not quite as different from each other, or the same, depending on which rear tire tracks with the left front and the direction of the turn.

Incidentally, before I put a front autolocker in the truck, I was worried what it would do to the turning radius when on the gas (locked). What I’ve found is that it doesn’t noticeably hurt it at all — not like putting the truck in 4WD, and definitely not like a rear locker that tends to cause dramatic understeer.