2001 F150 4x4 ext cab 4.6L Auto. I have extremely bad drive train vibrations above 75mph, noticeable at 50mph. So to trouble shoot, I removed the rear drive shaft and intended to drive it around neighborhood in 4hi to see if there was a difference in the vibrations etc. Do this on Jeeps all the time, so thought this should be okay here too.

Problem, fluid pours out of slip yoke seal without drive shaft installed. I need to know if this xfer case uses the slip yoke as its only rear seal. Or is the actual rear seal on the xfer case blown and it is just manifesting pouring out the tail shaft housing?

And then of course, the 4x4 doesn't engage at all. The lights come on, I can hear the differential trying to lock, but nothing at all from the xfer case. But, with the switch in 4hi, if I shift from neutral thru the gears and then try to shift back to park, I get a grind and clunk.

So, on this truck, I take it that both the differential and xfer case have to both work properly to get any movement from front axle in 4x4?

 

You can check if the transfer case or the front axle is your problem by putting the truck into 4hi and trying to rotate the front drive shaft. If it doesn't then the transfer case is engaged. There is a small shift fork in the front axle that is known for blowing out the tabs that allow it to engage the front axle. The part in the axle isn't too terribly hard to replace but can be extremely expensive if you buy it new (my dealership wanted $260 for it). I got one from the junk yard that I pulled myself for $18 out the door including the fork and collar.

Not sure about the seal on the back of the transfer case, sorry.