The auto tranny has manual hubs and the manual tranny originally came with auto hubs, so we assume you have a 5spd manual tranny.

My '86 engages the hubs within about 6" of forward movement and disengages if I back up about 3". This causes a bit of a problem on a hill when I'm moving slow and disengage the clutch, rolling backwards slightly. My hubs disengage until I start moving forward again. If my rear wheels slip, I don't move forward far enough to engage the fronts again. The cure for this is to move back far enough so they will engage before encountering the obtacle that stopped me in the first place -- sometimes clear to the bottom of a hill. Yesterday I rounded a corner and started up as snowy hill in 2nd gear. The snow and the hill combined to slow me down enough I needed 1st gear, so disengaged the clutch, shifted to 1st, and was immediately stopped by the deep snow, rolling backward enoough that the hubs disengaged. I couldn't move forward due to rear wheel slippage, so my hubs wouldn't re-engage. I had to back down the hill (thankfully there were no other vehicles on the snowmobile trail I was on at the time).

OTOH, you can't beat the auto hubs for convenience on snowy or icy roads. Just come to a stop, put the lever in 4Hi, and start up in 4wd. No slushy mess on your feet, no slushy mess on your carpet, etc. And you can shift into and out of 4wd after the initial lockup, without stopping. But be aware, if you stop (at a signal light, for instance), and roll back a few inches, your front hubs may disengage, and you absolutely should NOT try slipping into 4wd while moving again.

4wd is only for conditions where there will be wheel slippage. It does not give you better traction on dry, or even wet, pavement. Use it only where snow, ice, mud, sand, etc., are causing loss of forward traction.