Ever since I bought it, my expedition has had something in the driveline that has some kind of play or slack. Usually felt on an reverse to drive engagement, or most usually on a brisk takeoff from a rolling stop on a quick 2-1 or 3-1 downshift.

it will make a clunk and feel a bump like a sticky slip yoke, or possibly a bad mount bushing in the IRS center section. This is my best description of the noise and feel.

had it looked at by a guy has earned my trust over the years today. He checked the mounting in the center section, and pulled the rear driveshaft to check for play in the u joints. He did get it to make a noise and it sounded like it came from the transfer case area. So he checked the fluid and it was really dark, so he did a fluid change for me.

he said that chain was slack enough that the rear driveshaft would move more than 1/4 rotation before the slack was taken up. He said you could see the chain slacken enough that it would droop to the fill plug level.


Does this sound like it could be the source of my driveline play/bump?

i always thought that the chain just drove the front axle and any slack in the chain would only affect the operation of the front in 4wd. I always though the rear axle was more or less a direct connection to the output of the trans.

this is in a 2014 expedition with the auto 4wd. 120k miles. Everything else appears to be more less tip-top aside from a weeping axle seal at one of the rear CV shafts.

can someone school me a bit on transfer case operation? Or give a qualified opinion based on what I can offer by way of internet descriptions?

 

My old explorer did something very similar. It felt like there was a mile between reverse and drive. When shifting if you gave it any gas you could do a wicked, tire screeching burnout when the driveline finally caught up.

It never got worse or better and I managed to ignore it all the way to 260,000 miles when the engine went boom.

 

Well the TOD torque on demand transfer case is very sensitive to clean fluid. Pretty sure what you are feeling and describing is a failure in the clutch pack. The chain is very loose in these units and is not in direct contact with the rear. Remember starting in 2012 the new transfer case was able to transfer up to 100% power front or rear for traction using the clutch pack.

 

So I drove it in 4wd today to see if I could tell that the clutches were working or not. The roads were wet and I made a few tight turns on pavement with it in 4wd.

it definitely gets bound up some with it engaged. You can hear the tires scratching, and the front end pushes, and the drivetrain groans, but it didn’t hop like I would normally expect.

The other thing I noticed is that the driveline made the same “clunk” and “bump” when I went back to 2wd. It was repeatable every time I went back into 2wd and happened on the straight.


so .... is this a fix it or forget it?

 

The fix is a replacement transfer case. The clutches are in constant motion because they are inline with the rear driveshaft.

 

That’s what I’m trying to figure out, whether it needs to be replaced or if I can live with it.

the bump and noise aren’t particularly bothersome, so if it isn’t going to leave me hanging, I can live with it. But if it is going to fail and leave me in a lurch, then I’ll get it fixed.

it our primary family mover, and all around Swiss Army knife. It does get used harder than most, pulling trailers and our big camper.

plus, we were taking it to Yellowstone here in May, and will be pulling a small camper. And I don’t want anything to ruin the trip.

if it is something needs to be fixed, I’ll fix it. But if it isn’t a big deal, I can live with it.