I was backing up a trailer yesterday, and put the truck in 4x4 low. After the shift message went away I gave it some light throttle then heard a load clunk sound. The steering was turned pretty far to the right before I put it 4x4 L, and when I started to backup. Didn't like what I heard, looked under the fenders for anything wrong, put it back in 2wd, and pulled around the block to get a better angle backing up. Put it in 4x4 auto, and backed the trailer into my driveway. I felt some odd thumps when the wheel was turned close to full travel. Finished playing musical chairs with the trailers in the yard without further incidents.

Truck is a 2016 F150 4x4 SuperCrew 3.5L eco 6 speed auto w/tow mod 3.55 elect lock RR axle lifted on 325/60R20 tires. Truck was lifted by the selling dealer, and has been back to the local dealer for 4x4 problems before. Odd thumps and noises have been felt and heard before while turning sharply in both 2wd and 4x4. Truck is my mother's. I'm not familiar with 4wd trucks, or newer ones; I've only owned 2wd old trucks.

 

Were you in neutral before shifting into low? If not the gears probably didn't fully seat until you started moving, hence the clunk.

 

 

I was on loose gravel, small less than 1" diameter smooth round stones 6-8 inches deep, and snow covered grass. Would the drive line binding cause damage?

I'm aware of the neutral requirement, the dash tells you to shift into neutral.

 

 

Clunks and lurches going in and out of 4WD are almost normal for these kind of systems. Because they're not fully engaged all the time like an AWD system, gears have to mesh and parts have to come up to speed if the truck were moving.

Shifting to 4-low from a dead stop makes for a tough shift in the transfer case because the gears may not be lined up to mesh when you turn the switch. When you apply power, the gears probably meshed suddenly and engaged hard. Hard turns are harder on the system, as is engaging the system from a dead stop. Next time try shifting to 4-low with the wheels straight before the traction is needed, and do so with the truck slowly rolling from 1-3 MPH. The owner's guide should say this as well.

 

Between the increased gear ratio of L, the tcase and IWE's locking in, and having the wheel turned was probably enough to cause a less than smooth engagement. If you start to notice it more often, in more idea conditions i would worry then but it doesn't seem like an issue.

 

Thanks for the input. The manual does say to be going less than 3mph before shifting into 4L.

 

mrollings53,One other thing make sure the Trans is in Neutral rolling 3-5 Mph to mesh gears.
Than put in 4L I don't think you did any damage, So now you know the Procedure