So I've ran into a bit of an issue with my 1993 Ford F350 4x4 7.5 V8 e40d recently. I have had a chirping sound that only occurs after the truck has been put into 4x4. When I take it out of 4x4 the noise continues until the truck is shifted into reverse and backed a bit. After that the noise never comes what so ever when in rear wheel drive. I have narrowed it down to the front of the transfer case. I checked the level and it was significantly low, so I went ahead and filled it up. I have driven about 15-20 miles since filling up the t case and the problem is still persisting. But like before when I'm in 2x4 it won't come on unless put into 4x4. I need the truck for an upcoming hunting trip so I am kind of at a loss here. I am having no issues driving it out on the roads in rear wheel drive. The truck shifts perfect all the time. And it shifts into 4 high and low no problem. Everything transmission/tcase related operates as it should. Should I be concerned? Could the truck potentially need to be driven more to further lubricate the front of the t case? I have somewhat ruled out the U-Joint since it is in relation to the four wheel drive. Could it still be the U-Joint? Is it okay to drive in rear wheel drive if it's not making the sound? Thanks in Advance!

 

Possibly a compound issue? Sounds like it could be the front driveshaft ujoint accompanied by a locking hub that may be sticking. Just a wild guess here.

 

Based on the chirping continuing after you shift into 2WD and stopping when you back up, I'm assuming you have automatic front hubs. So you are getting the chirping whenever the front driveline is turning, whether you are in 2WD or 4WD.

I'd say the most likely culprit in that situation is a U-joint in either the front driveshaft or the front axle. (You say you've ruled out the U-joints, but I don't see anything you've said that would suggest that it's not a U-joint.)

As a next step I'd suggest pulling the front driveshaft out. That's not very hard and it'll let you check the U-joints on the driveshaft better.

If those U-joints are OK, then try driving the truck with the transfer case in 4WD (with the driveshaft still out). If it chirps then you know it's in the transfer case.

If the driveshaft U-joints are good and it doesn't chirp in 4WD with the driveshaft out, then it's likely in your front axle which is a little harder to dig into than the driveshaft.


edit: I don't see anything really pointing to a hub problem either. Not that there couldn't be one, but the only thing you said that relates to the hubs says that they do unlock when you back up in 2WD. So we'd need more info about what they may or may not be doing before we could say if there's actually a hub problem.

 

Please elaborate on the chirping sound. Tire chirp? Metal to metal?