Hi all: I have a "02" screw lariat 4X4 5.4l that i purchased used about 6 months ago from a dealer. it has had a vibration since i got it that seems to be only around 1400-1750 rpm.(You can feel it in the steering wheel, floor, seats,etc...) not real bad,almost like a humming type vibration. the dealer put on new tires, took off the dual exhaust and put on a new factory exhaust, (said the exhaust was mounted too rigid and causing the vibration) all with no change. original Dealer suggested I take it to another dealer for a second opinion since they could't find anything. second dealer said 3 coils were losing signal and causing a miss. dealer replaced 3 coils and vibration still there. I had the truck in the air to rotate tires today and noticed if i spin L/F tire, front driveshaft turns. I reached under and grabbed front driveshaft and it stopped turning, but the R/F tire started turning. I started truck up to insure vacuum was correct for hubs (electronic shift 4X4 w/ no manual hub locks) and same results. I had my wife hold the try to hold the R/F tire from turning while I spun the L/F tire and held the front driveshaft, and she couldn't keep the R/F tire from turning. Is this normal or have I mabey found the source of my vibration. Are my front hubs locked and turning my front driveshaft as I drive? Thanx for any insight...Carl

 

On the 97-03, the axles should turn. It has a center disconnect at the differential. As long as the front drive shaft does not turn, you are okay.

 

Hi Kingfish: Thanx for the reply! To be sure I understand you correctly, are you saying that if I turn both front tires (as if I am driving down the road) the front driveshaft should Not turn? Thanx ,Carl

 

Hi all: I just went out and checked, if I have the truck running and spin both front tires (by hand using an assistant) as if i am driving down the road, the drive shaft is also turning. If I grab the driveshaft and try to keep it from turning, it makes one of the front tires stop turning...Normal? Thanx, Carl

 

That is not normal. The axles should turn, but not the driveshaft. Sounds like the front diff is not disengaging. Problem could be caused by multiple things.

 

Thanx again...I will let you all know what I find out! Carl

 

Do a search on 4x4 not working. What causes it not to disengage is just like what causes it not to engage. I doubt in this case its is a problem with the transfer case as you did not state that the front is binding up in tight turns. More likely to be a problem with disengage solenoid, vacuum motor, vacuum leak on the line to the diff, or engagement fork.

 

Hi Kingfish,

Thanks for all your help, I tried to send you a PM, but I guess I'm not allowed to use that feature. I looked at the solenoids on the firewall and guess what, the one on the inside with the pink and the black vacuum hoses had the pink hose unpluged (the one that goes down to the axle disconnect). I plugged it back in and the axle disconnected... Many Thanx

One more question if you would..The snake loom coming from the axle disconnect has green, pink, and black vacuum hoses in it. Pink comes from the axle disconnect solenoid, green comes from the axle engage solenoid, and the black one is just hanging out between the 2 solenoids not connected to anything and it has no connector on it, just a piece of black plastic vacuum tubing, with no rubber end on it. Any idea where this is suppose to go?

 

I traced that black unconnected plastic vacuum tubing down with the green and pink vacuum tubing where they all meet as a connector/plug and the black plastic tubing looks like it becomes a piece of rubber hose, which then runs to the front axle. Am I right to assume that this is just a breather for the front axle?
Thanx, Carl

 

Sure sounds like the brather.