When engaging from 4x2 to 4x4 high on the move , let’s say at 20 MPH, I turn the **** and I hear a series of clicks in my dash , or under it , then after a delay of few seconds, 7 to 8 seconds the 4x4 engages violently .
When I say violently I mean a big Bang , wahmmm in the front end , then I get it on 4x4 with the display light in the dash.
Does anybody know or have a clue what can that be ?
This is on my 97 F150 4x4 with a 4.6 L V8 Automatic.
* The front differential has new fluid I replaced back in 08/07

 

That doesn't sound right. I know the owner's manual says you can shift into 4-Hi at any speed up to 55 mph, but maybe go slower than 20 mph.

 

i was always told be complety stopped and in neutral to go to 4hi. or low.

something bout the rear diff. will be spinnin and since the front would all a sudden be thrown to the same speed would cause to blow it out and make the poppin noise. seen it happen to bunch of big 4x4 quads

 

You are correct , but we are talking about going from 4x2 to 4x4 High.
Going from 4x4 High to 4x4 Low , you must be in a complete stop and preferably on neutral.

 

were you on dry pavement?? 20 mph in the snow or mud should engage no problem. i remember my 97 took about 5 seconds to engage.

 

Yes, Dry pavement, but either way I don't think engaging in to 4x4 is followed by a bang that sounds like the front differential just blew up.