working on buddy's 99 Nav Awd

he is complaining of a intermittent grinding sound and vibration at highway speeds. from what I can tell the 4x4 is not always on, it seams to be coming on on its own causing the trouble at highway speeds, Today I could not get the 4x4 to dis in gauge, the front wheels would not spin when off the ground?

Two days ago I could not get the noise or vibration when I test drove the truck. I did the same test at that time the wheels would free spin!

So is the transfer case motor bad or is something else telling it to come on at wrong time?

Is there a way to dis in gauge the awd so he can drive in 2wd?

 

There is a circut breaker in the power box under the hood, check the owners manual to find which one to pull. That will disengage the system electrically. If it still seems locked in there is a mechanical problem to locate and fix.

 

Its fuse #104

 

I'm not 100% sure, but i think the '99 uses the vacuum acutuator on the front axle to lock (similar to the F-150). My 98 had that set-up. It's possible that this acuator is stuck in the locked position. This would cause your front axle to be engaged but your transfercase isn't ( would be like engaging your manual hub locks, while driving with your t-case in 2wd)

My '98 had the opposite problem. the actuator was shot, so even though my t-case worked fine, the front axle never locked, so i was in 2wd even when my t-case was in 4wd.

Should be easy to check. just remove the plastic cover on the front axle ( near the center, toward the driver side) and watch it while someone switches the running truck from 2wd to 4wd. If it moves over when switched it should be working, if it doesn't, or moves to one side and springs back it isn't working properly and you could have an issue with the acuator or one of the two solenoids on the passenger side firewall. You could also have a vacuum leak in the lines

I ditched the whole system and replaced it with a manual cable actuator made by Posi-lock. you can see more info here. I have been using this regularly for the last 5 months or so, and so far am very pleased.

 

Pulling this fuse seamed to help, he is going to drive it for a few days to see what happens!


From what I can tell ther is no hubs looks like the cv axle splines right in to the bearing.

 

That's correct. On these vehicles the front axles are always engaged to the wheels. On models with a 2H selection on the dash, the only thing that happens is the front differential ring gear is disengaged from the axle, while the transfer case cuts power to the front driveshaft via an electric clutch. This clutch is powered by fuse #104, so with that fuse out you will not have A4WD or 4WD at all.

 

So pulling the fuse, stopped the problem! what do I need to look at next? is it the transfer case motor or is some thing else faulty telling it to turn on?

 

The good news is the problem is not with the transfer case or the shift motor. It's a problem with the selector switch on the dash, the 4WD module, the wiring for it, or the tires front to rear on the vehicle are not matched. First see if it's the tires by swapping the front and rear tires ON ONE SIDE ONLY, then take a drive (with fuse #104 installed) and see if the problem is gone.

 

So he wants to put a transfer case motor in, Is there any thing I need to know?

 

I had a similar problem in my 99 navigator. Only made the noise at 45mph+, and usually when i was pulling a hill. Pulling the fuse stopped the noise. The shift motor fixed mine. It was fairly easy to swap it out. It is bolted on externally toward the rear of the transfer case.

 

Changed the TC motor, still get knocking from the front axle. Pulled the fuse, still knocked! once we backed up a few feet the knocking stopped?

What turns in 4x4 that don't turn in 4x2? The CV axles turn all the time. I think the front drive shaft does too?

 

Ches post #8 talked about cking the the tire sizes (different sizes probably throw off comp module), dash switch, 4wd module, did that yet?