4LO sometimes works after fluid change
So I found a sweet deal on craigslist - a 97 F150 4x4 for $600. The problem? The owner thought the transmission was going to die. He was wrong, and I knew it after test driving.
4.6L, 4R70W, Borg Warner 4406 electronic, 3.55 open diff.
Upon test driving it, I checked both 4HI and 4LO. The transfer case (BW 4406) shifted smoothly into both, and everything seemed to drive ok. The seller notified me that there was a slight t-case leak. For $600, I wasn't about to care.
In preparation for a road trip with Betty (her new name), I changed out the rear differential gear lube and the t-case oil.
Here's the strange thing: when I pulled the check plug, about a gallon of ATF drained out. All in all, there were about 12 pints in there somehow. I'm guessing the last person that filled it was going with the fill amount for the 1356 W/ PTO, which is somewhere around that amount. I refilled with exactly 4 pints of MaxLife ATF, hoping to aim at whatever might be leaking.
After the change, the t-case shifts just fine into and out of 4HI; however, turning the selector to 4LO does not shift as it did before. Before, I would let the truck idle along at 3-5mph in 4HI, and then select 4LO and shift to neutral. It would pop right into 4LO.
Using the same method now returns mixed results. I thought it didn't work at all, but then I put it in reverse and it shifted into 4LO like normal. I put it back to 4HI and tried the same again, and it didn't repeat. I tried a couple different ways, but whenever it shifts to 4LO it doesn't seem to be repeatable. It seems to just decide whether or not and when to shift into 4LO when the selector switch is on 4LO.
Should adding a bit of fluid, perhaps up to the check plug, iron this problem out? Or is something else going on?
The only other thing I can think of as a possible problem was that the girlfriend drove down the mixed wet/snowy highway for about 60 miles in 4HI with the selector in 4LO. For obvious reasons it didn't actually shift into 4LO but I thought I should mention it.
Thanks for any suggestions.
P.S. I'm new to 4x4 vehicles. Is it normal for there to be a low hum coming from the front driveline when 4HI is engaged? And when I disengage 4HI, something in the driveline doesn't disengage until I come to a complete stop. Normal? Lastly, I have a bit of front wheel hop in 4HI while backing/turning into a parking spot. Are these things normal?