I've had probs with my 4x4 not engaging. I checked the vac lines and replaced the vac solenoid,Didn't help.When I turn the **** to engage the light COMES ON,click in the dash,and I can here the shift motor makes noise. I took the shift motor off,marked the internals to see if it was turning when I turned **** and it is. It seems to me that the shaft going into the trans case appears to have some "slop" in it like it doesn't know where to stop in 4hi or 4lo. I turned the shaft by hand to 4hi(it's marked on the case by the input shaft) and it worked fine. I guess my question is would it be the motor if my lights are coming on on the dash or does it sound like prob in the tcase itself.I thought maybe if the motor was going out it just might not be turning it all the way to 4hi or 4lo

 

I would say it would be the shift motor over the t-case. On mine the shift motor would work sometimes and sometimes not. I started engaging it more often and it seem to work all the time but i still had no 4 wheel drive. I winded up replacing the shift fork in the front diff. It has little nylon things on there that wear off and the fork doesn't slide the sleeve over all the time or it will pop out. It works every time now.

 

Not enough info. What year is your vehicle? When it is in 4x4, does the front driveshaft turn? If 97-03, it could be more than just vacuum. It could be the shift fork in the front diff, the vacuum motor on the front diff, etc. If o4 up, it could be the IWEs.

 

It's an 06 xlt supercab 5.4 with 77000 on it. I could turn the output shaft on the t-case by hand and it would engage and not "pop" out of 4 wheel

 

Then definitely transfer case or shift motor.

 

Its really hard to say with out playing with it and getting my eyes on it. To me, it sounds like the shift motor is not properly engaging, but this is really just a shot in the dark.