front end noise

[john bo]

Hi. I have looked over many threads and have not found a post exactly like my situation yet (but are probably there).

On my 96 5.0 AWD, I get a very loud wup-wup-wup noise with rotation coming from the front end. It is there with acceleration and deceleration. Doesn't seem to be coming from a particular side and is not effected by turning or steering. It IS speed dependent, coming on at about 25 mph, is the worst (a very loud dull roar) at about 50 mph and is better at 65, but still loud enough. It sounds like a u-joint noise, but I checked all I could find and could find no play. There appears to be a little "wetness" right at the left exit of the front diff, but no active leak and the front diff was not too low on fluid. (topped it off and no real difference). Vibration does not seem to be much of an issue and the vehicle goes down the road just fine. No real driveability issues. No clicking, clunking,squealing, or grinding.

Here's another thing: The front driveshaft gets hot! Not too hot to touch, but hot enough where it is uncomfortable to grab and hold for any length of time. So, I'm thinking somewhere between and possibly including transfer case to front diff.

Any hints or diagonotic help is greatly appreciated.
Thanks.

 

[drdoom]

I would pull the hubs and see if they are getting rough.

 

[drdoom]

How about the transfer case fluid? Checked or changed?

 

[Dave 1955]

Could just be the tires.

 

[john bo]

Thanks for the replies, guys. Didn't look at hubs, yet because it did not seem to be coming from a particular side, but if both happen to be equally bad...? Did not check the tcase fluid - next on my list, thanks. Did check tires, both appear to be like new, may try running my hand over them again. No pull of any kind to a side and coasts nicely (like its easy to slow down a 4000 lb vehicle). Don't know a lot about the service history - just bought it with 13?k on it.

 

[john bo]

OK... update:
Checked it out a little more. Noise is definitely mechanical / metallic and loudest from inside the truck. Rode with both windows down and definitely not coming from one side or other, so not hubs or tires. Passed the figure 8 test with ease and noise did not get any better when on dirt /gravel, so doesn't look like VC problems. No change with breaking, so doesn't look like calipers. Still didn't check tc fluid because it was kinda dark when I got to it and didn't have a flashlight. I did chase down the heat by feel. TC - not hot. Front drive shaft - hot. front diff - hot where the ds enters, but not as hot as DS and gets cooler as you get away from the DS. The hottest part was the splined yoke, I believe you call it. So I'm leaning toward that. I will probably drop that and I see where some people have installed a zerk fitting for lube. I'll probably try that, but I am concerned it might affect DS balance.