2001 Ford F150 Lariat 4 x 4 5.4 L
4R70 Transmission

Status
Truck sits all night
Start Engine Will transfer to 4x4 high, 4x4 low
will transfer back to 2 x 4

Drive Truck a while
Will NOT transfer to 4x4 high, 4x4 low

Truck Sits a while
Will transfer to 4x4 high, 4x4 low
Drive in 4 x 4 a while
Will NOT transfer out of 4x4 Low or 4x4 High

Truck Sits a while
Will transfer out of 4x4 Low and 4x4 High

When it tries to transfer, I hear the clicks like a relay clicking on
After three it stops and nothing happens again till it cools down

I thought it would be the Motor, so I had a new one installed
Still have the same problem.

 

Oh I do not have the vacuum lines that go to the hubs
nor the vacuum relays.

 

I'm almost wondering about an internal issue in the t-case. I'd be tempted to tear into it but FIRST when it WON'T shift I'd probably unbolt the motor and see if it will THEN move to the appropriate position.

If the motor is NOT moving to where it should, then you've still got an electrical or wiring issue. If it DOES that suggests it's incapable of moving the worm gear in the 'case due to a physical obstruction like a worn shift fork or something.

I haven't heard of internal 'case failure that'd be temperature sensitive, but there certainly are different materials that expand at different rates, soooo maybe....

 

You have a center disconnect. Inspect the vacuum relay and hose going to the diff.

 

True enough, but if he's truly not getting in or out 4lo, that's not a CAD/FAD issue.

 

So Im wondering if the road growling I hear is related
to the transfer case. ( replaced all front wheel bearings and checked tires)
If memory serves this started about same time 4 x 4 issues started

Im not sure I under stand how the 4 x 4 engagement works

So you switch it to 4 x 4 high
This cause the motor to rotate and engages one of the vacuum relays
to lock up the diff. ?

What causes the light to turn on indicating the truck in in 4 x 4 high
Does this come from the motor rotating into correct position?
Why do I get multiple clicks then nothing. does the motor in position then cause
the relay to engage?

So if the motor was trying, but not being able to hold it in 4 x 4 low would this cause
the relay to go in and out

 

You might check Posts #10 thru #13 here
https://www.ford-trucks.com/forums/9...97-2003-a.html

Regardless, it's important to understand the system has 2 major pieces, and they can work independently:

1) something has to physically lock the front axleshafts (or CV shafts in this case) to the front differential. Here, it's accomplished with a shift fork actuated by vacuum that slides a collar to connect the right front axleshaft that has essentially been "severed" at the factory. When a collar bridges across both pieces, they become one shaft. This is the same as "locking your hubs" on old 4x4s before we became too fat, lazy and ignorant as a society to do that anymore. THIS DOES NOT MEAN YOU HAVE 4WD - IT MERELY MEANS THE FRONT DIFF and driveshaft NOW IDLES ALONG WITH THE WHEELS AS THEY SPIN DOWN THE ROAD. This also does not hurt anything to run with the "hubs locked" -- it simply makes for SLIGHTLY more rotating mass and thus a mostly theoretical drop in MPG

2) this is arguably the most important: the transfer case (located behind the transmission) slides a collar internally so that it now POWERS the front d/s. Note that "POWERS" is the most important word here because this where you begin to actually send POWER to the front wheels and that is the magic of 4wd.
However, if your front diff has not engaged the CAD (Center Axle Disconnect) that power is going to My Cousin Vinny: it's like one wheel is spinning in the southern mud and one wheel is on solid ground (because the front is an "open" differential, vs an aggressive "posi", true locker or spool)
If this is occurring as it should the front d/s will effectively become one with the rear d/s, so if you're in 4wd, elevate the front wheels and have the vehicle in P you shouldn't be able to rotate the front d/s because the rear also cannot spin under these conditions

Either #1 or #2 can occur and it doesnt hurt a damn thing, but you don't get actual 4wd until BOTH #1 and #2 occur. Knowing this helps IMMENSELY with troubleshooting because it's easy to check underneath with a floor jack, common sense and caution which is happening and which is not.