2015 f150 xlt 5.0 4x4 but not auto, 9.75 rear end 100k miles.

I’m having issues with the 4wd on my new to me truck. It shifts into 4 high and 4 low without issue, decent bang as it shifts but shifts quickly. My issues start trying to get out of 4 low into 4 high.

With a very slow downhill straight roll it will sometimes cycle through ok but half the time won’t get out of 4 low, It might show it’s in 4 high but when I try to go to 2wd it indicates to pull forward and when I shift to drive I’m greeted with a loud grinding noise from the front end, I get the same grinding trying reverse and I get a racing idle of about 2500rpm for a few seconds too.

I shift back to 4 low to start rolling forward in gear before shifting back to neutral and repeating the process until it will eventually get 4 high and normally with some use of brakes and acceleration it’ll finally get 2 high.

This seems like a lot of work and noise for a clean good condition truck, I’m use to finicky 4x4’s but this seems more like a malfunction, any ideas on what to check first? No error codes or dash lights unless it really fights shifting up to 4 high then I’ll get the check 4x4 wrench icon.

Many thanks, Dave.

 

Check your fluid levels?

 

I know descriptions of problems like this are difficult to spell out, so this may just be a phrase thing. You stated slow roll. A shift to or from high to low should only be attempted at zero speed. I don't remember the specific words in the owner's manual, but using neutral or park, preferably without any binding on a hill would be preferable. It takes my truck about 10 seconds to make the switch.

 

You should only switch to/from 4Lo when you're stopped (Ford OM says under 3 MPH) and pretty much have a straight line roll for a few feet. The transfer case gears can get in a bind that will prevent the solenoid from releasing the mechanism. After you switch from 4Lo to either 2Hi or 4Hi, slowly roll forward or backward to unbind the transfer case. Switching from Drive to Reverse and back can also help. I works better if you make the switch while you're on soft ground with some give--all 4 tires on paved surface aggravate the problem.

 

I've found that transition happens most easily when the vehicle is barely rolling in Neutral. When completely stopped it might be bound up just a bit.