Feel like what ever tinkering I do on the disco, the prop shaft comes off

 

Greased the propshafts, front and aft, no change in behavior.

I am fairly confident it has to do with the viscous fan decoupling and freewheeling. Anyone have experience with this?

 

Did you drive it with the front shaft out? Depending on this issue, grease might not eliminate it. That's one of those deals where if you solved it then great, but if grease didn't solve it then all you know is that grease didn't solve it; it didn't prove that the part is fine.

It sounded like you were tying the noise to road speed; that would argue against the fan clutch. That you might get more info by holding the trans in a lower gear to see if it is really road speed or engine speed or load.

 

The reason I currently believe it is the fan making the noise is because it seems to sharply begin at around 30-35kph. If I drive around at speeds around 20kph, no noise. Above ~30kph it is present and its frequency increases with speed (Ram airspeed). I'll pop the fan off and confirm.

 

Drive shaft noises are often speed dependent. If the shaft is roasted then all the grease in the world isn't going to make it better.

 

It's a brand new lucky8 shaft. Always been greased, topped off today.

 

Your logic is invalid. The only way to prove something is not bad is to prove that it is not bad. You haven't done that. If that is the way you want to roll then go for it, but just don't fool yourself into thinking that logicing your way through a problem diagnosis is the same as proving your way through it. You might well be right, but all of us have gone through being certain (read that as thinking wrongly) that we know something is good when it is the exact thing we are trying to find as our problem. Good luck going forward.

 

I've had a L8 shaft go bad in an extremely quick amount of time like less than an oil change with proper greasing. Age of a part means nothing these days.

 

Did you check the tensioner on the left side of the engine (facing the vehicle? Have you wiggled the fan clutch with the serpentine belt off?

I’m with everyone else on the front shaft, though, especially if you recently replaced it. I’d check all your bolts at the diff and T case end and keep going with the grease gun, or fully pull the shaft and inspect the individual U joints.

 

Hi All,

Checked front shaft, wasn't it. I did however find the source of the noise after taking out the transfer case output shaft bearings.

The front mud shield had deformed and was loose, periodically spinning with the output shaft and grabbing onto the seal. You can see how the shield has been damaged from the grinding.

Really nice to have found the source as it was driving me nuts!

Hopefully someone in the future can find this thread and find the issue quicker.