I was told by an old timer to stay away from 4X4 AODs. He said that they don't hold up. I gave no way to verify that. Of course I'm sure that they can be built up to be stronger.
I believe the reason he said that was from experience....repeat or pattern failures...I have a couple of thoughts on that which might shed a little light on the situation...
The early AOD had two input shafts...both splined to two different parts of the torque convertor...the center one was splined to a damper assy. affixed to the front cover...looked like the hub and spring setup on a standard shift clutch disc...
The other shaft was hollow...because the first shaft rode inside of it...but the second shaft was the one that would connect you up from the TC impeller to the Forward clutch...and when you were in Reverse, First, Second, and Third (direct drive)...the powerflow was through that clutch...
Once you were in Third,(direct drive)...the effect was the same as if you were in 3rd in a three speed manual or 4th in a four or five speed manual...you had a direct connection from the crankshaft of the engine to the driveshaft and rear axle pinion gear...all of that driveline is spinning as one unit...
All well and good...as long as you were moving along faster than ...oh...say...45 MPH...
BUT....on coastdown...if the unit stayed in Direct Drive...you would wind up lugging the engine...just as if you had a manual trans and forgot to downshift on coastdown....
LUGG...LUGG...LUGG...etc.etc...that kind of torsional vibration...well...you know...not good for anything...tends to beat up stuff and generate drivability compaints...
The early units had a calibration problem where they would hold a higher gear range longer than they should have...
It was bad enough with a passenger car...with tire heights kinda short (compared to trucks) and final drive ratios from 2.50 to 3.25...
BUT...now put that unit in a truck with taller tires...more weight...and not-very-steep final drive ratios...NOW you have a real dog...
The fix is to recalibrate the unit to upshift and downshift on time instead of lazily...and to gear the vehicle better...and if it is 4x4...well...make sure to re-gear front and back...to a better ratio...starting at about 3.73-to 4.10...and keep your tire height more reasonable instead of nosebleed high...
One thing the aftermarket did was to eventually offer an input shaft that omitted the center splines but attached the direct clutch pack to it in the back of the shaft...more like the shaft in a 4R70...but you would lose some RPM reduction in 3rd and 4th...
So...yeah...if I had an early 80's Ford truck with an AOD...I could fix it so it would hold up just fine...but the fix would not be only in the transmission itself...you have to gear the truck for its intended usage...
And...it helps if the engine is resistant to lean or too-far-advanced timing misfire...
Just my .02
P.S. as an aside...the geartrain in the AOD is similar to the one found in an FMX...good ideas just seem to live on and on....