I have a 2002 F150 Lariat 4x4 5.4 that is in pretty good shape and I've had it all of it's life. I plow my business in the winter so it gets a pretty good workout, but don't use the 4x4 low range the rest of the year. Something that I've noticed is that it is becoming slow to engage or disengage. 4x4 high range is not problem and will easily change on the fly or slow driving. But, the 4x4 low range has become worrisome as it can take up to a couple minutes or more for it to drop in. I've tried backing it up for about 50 feet then popping into neutral and going forward doing the same thing and nothing happens. The after awhile I can just let it set there in neutral and suddenly it will engage.
I'm wondering if I have an engagement shaft under there that is gummed up and needs some lube or something. Anyone have any experience with this that can offer something? Sure would appreciate it as more snow is coming.

 

Do your brake lights work? Not only does it have to be in neutral, your foot has to be on the brake for 4 Low to engage.

The only mechanical difference between 4 High and 4 Low is internal in the transfer case. Everything else is electrical.

 

Thank you, GLC, for the response. You saved me a lot of time crawling around under there only to find there was nothing to find. I'll use the brake pedal when shifting to 4L this time! Funny, I've used the truck for plowing since it was new and don't remember ever doing it.

Thanks again for the help and I'll report the results.

 

Just a quick note to close this thread out. I used the truck today and tried putting it in 4L by putting it in neutral AND pressing on the brake while turning the ****. What do you know. It went right in!
Duh...
Anyway, thanks for the input.