This morning it was raining very hard so I decided to put my truck in 4X4 (4.6L Auto trans with 4X4 floor shifter). To my shock, the truck did not go in to 4X4 but the light came on. I tried everything to get the darn thing to engage (turned wheels and moved forward, braked hard, etc.). Even tried stopping, neutral and 4X4 LOW range.... squat. I put it back in 4X4 high for a little bit and when I went over a few bumps, it finally engaged after about 10 miles or so. This never happened before and I used the 4X4 2 weeks ago in a really hard rainstorm on a muddy road. All fluids are good (Transfer case, differentials, tranny). Could the hubs be sticking? Do the hubs require greasing? I have babied the heck out of the 4X4 and a couple months ago, I had to have the rear differential re-sealed due to a leaky seal. The mechanic at the shop said that the underside of my truck still looked new and all the fluids were full and and colour was good (nice red for Transfer case and golden brown for the differentials.... all synthetic fluids). Any info would be appreciated.

1997 F-150 4X4 X-cab, Regular box
4.6L Auto with 4X4 floor shifter
O/D button on column shifter.

 

i usually stop, put it in gear, and do a burnout to make it ingage... that usually does the trick...mine just won't dis-engage

 

The hubs work off vacuum. Check your vacuum lines with a meter. I had one that was cracked behind the battery tray, and was causing the 4x4 not to engage.
Good Luck