Not so fasr, what abour the 2 rar u-joints on the rear of the front drive shaft located inside the double cardon housing? If not, you shop doesn't know what they are talking about and you need to get it rebuilt properly with 2 new u-joints and a centering ball.

 

All 3 u-joints have grease fittings and the ball joint looks excellent. I had the shaft rebuilt about 3 years ago.

There is no play in any of the joints installed or removed and there is no indication of wear on the ball (the surface is shiny smooth.)

 

I put the shaft back in the Disco and drove it over to the shop and there were "bonus" noises.

When I back up there is a noise on an interval.
Normal forward driving under power also now produces a mechanical noise on an interval.
Letting up on the gas sounds really bad, like a propeller.

We are speculating that the propeller noise on let off only is the result of gear lash combined with something being broken. So the theory is that when power comes off, the gear lash provides play and combined with whatever broke (bearing maybe) there is excessive play and that is generating the propeller noise.

When you are in the vehicle the sound is definitely directionally from the front center. You tend to point straight at the diff when you locate the sound (from inside of course).

The Wheels counter rotate properly when on a lift. There is no mechanical noise when doing short duration rotations. (I will try longer ones like 10 or to see if something pops up.)

There is no vibration at all from the drive shaft (or anything else). Even when the propeller noise kicks in there is very little vibration. (With the amount of noise that is generated the drive shaft would be rocking the boat if it was the source). There is no feedback to the shifter or the transfer case selector when the propeller noise kicks in either.

 

Have you pulled the rear covers or at least drained the gear oil and inspected it yet? Sounds like you're narrowing down your cause. Seems like you'll find it in there.

 

That is next. I am going to check the drain plug for metal.

 

I dropped the front drive shaft and engaged the CDL and took it out for a ride. Got the same noises. Since the hubs don't unlock they are rotating the diff. I had hoped to drive it while I looked for a donor 3rd member.

To me this seems to confirm the front end. Any other thoughts?

Thanks,

 

That's a strange thing to do before you've checked if the front diff plug and oil is full of metal, considering it took a whole lot more time and was going to be less conclusive.

Seriously - drain the oil. You won't have to ask anyone for advice if it comes out full of metal. Until you check that very simple thing, you are just guessing around the problem. This will take you under 60 seconds if you already have the tools in you hand. Less time than it took you to post.

 

Thanks Daryl, it was a logistics thing with the fluid and driving it. I didn't have any to replace it and I needed to drive it if possible.

So I drained it and there was NO METAL....not one shaving. The fluid was in excellent condition too.

So currently I have the front drive shaft removed but I still have the noise. My assumption is that the hubs are NOT spinning freely and therefore are rotating the differential. Am I wrong on that?

 

Right, the hubs are not free spinning hubs, so the side shafts and diff are turning.
Time to pull the diff and eyeball it for damage.

 

I had to go back to square one and assume that I was mis-interpreting the direction of the source of the noise.

I had the front drive shaft removed and CDL engaged and I blocked the front end front and back and put the rear end on j-stands with a support floor jack on the diff. I rotated the wheels and could not hear anything. I started it up and put it in D1 and let the wheels spin and I could hear in the interval noise. I put my finger on the t-case housing and I could feel the tick. Turned it off and drained the T-case.

It spilt it's guts.

So to the RAVE Manual we go. I have dropped Jeep T-cases but this one looks like it might be a bit of challenge.