Very nice summary there EXT4ME. The one part I take exception to is:
To my knowledge, there was never a OEM front locking differential available on any Avalanche. I'm not even sure there were any offered aftermarket. The G80 rear mechanical locking diff is very common, however.
I could be wrong.
It happens more than I would like.
My understanding is the front differential on a 4WD Avalanche uses an electronic actuator to lock a normally free wheeling, passenger side CV axle shaft to the differential when 4WD is activated.
In normal 4WD mode, 4-HI or 4-LO, both front CV axles shafts are being turned from power coming from the transfer case via the front differential, which is not an open differential and therefore does not allow slippage between the two front drive axles.
This would cause both front wheels to effectively be in lock step and would not be advisable while driving on dry, high traction surfaces.
When 2WD is selected, the transfer case is disengaged and the front differential actuator disengages the passenger side CV axle shaft from the front differential, allowing that shaft to spin independently of the front differential and the driver's side CV axle shaft.
Someone can clarify exactly which components are engaged when 4WD-Auto is selected, but my impression was the front differential actuator is disengaged and the transfer case actuator is engaged.
When loss of traction is detected, the front differential actuator engages, effectively placing the system in full 4WD until the low traction situation has passed.
With the passenger side axle shaft disengaged, it can once again spin independently of the driver's side axle shaft, but the transfer case remains engaged.
This mode would seem to place undue wear on the transfer case and reduce gas mileage during driving times when not actually needed.
But, that's the way I understand it and I could be mistaken.
What I know?
It may also be important to note that the G80 rear differential is sometimes erroneously referred to as a "limited slip" differential.
When in fact, it is a "locking" differential that uses a centrifugal locking mechanism to effectively lock both rear axles together when enough wheel spin is achieved.
A true limited slip rear differential uses a wet clutch pack system that holds both rear axles together all of the time, but the clutch pack allows each rear axle to slip as needed during turns.
That is why a "friction modifier" is added to the rear end lube of a limited slip differential.
There is no such wet clutch in a G-80 and therefore does not require a friction modifier.
When an Avalanche is being driven in 2WD mode or is just a 2WD truck and no excessive rear wheel spin is happening, those trucks are both open differential 1 WD vehicles.
Just like any other open differential rear end vehicle out there.
