Drive Train Noises - But From Where?

I got this from a friend who owns a modfied 1966 V6 CJ-5. He's not active on the forum yet, so I'm posting this here for him (and sending him a link to the thread to entice him to join!) His question is beyond the extent of my knowledge, particularly as I have no experience with the Muncie 4-speed. Any help would be very appreciated!:

I had the Jeep in Georgia a couple weekends ago and drove it on a 60 mile round trip drive to pick up some processed deer meat and on the return I noticed a whine that sounded like the tranny (Muncie SM465 4 speed), but it was very high pitched and not loud. The tranny already made whining noises through the gears that I assumed were normal. As I slowed to turn a loud groaning noise seemed to come from the tranny but as I picked up speed it disappeared. I heard it again as I slowed to pull into camp. I flat towed it home as usual (transfer case in neutral) and once home drove around block to park in garage...no additional tranny noises. Spoke to my mechanic who suggested changing gear oil in tranny and bring by for him to listen to it(which I haven't done yet).

In mean time, I put TC in neutral and ran through the gears...tranny was very quiet...no whining at all. I assumed because no load on tranny. So I took it out the other day and drove 15 miles or so on local roads and interstate up to 70 mph. No noises other than normal whine. Back in driveway again put TC in neutral and ran the gears. This time I was hearing what sounded like marbles bouncing around in tranny only in 4th gear, not the others. Thought maybe this was because there was no load and 4th was just rattling a bit. And only for a few seconds I was able to reproduce the groaning sound when coming off throttle in neutral and clutch engaged. Groan disappeared when clutch pushed in. Back on the road was not able to reproduce the 4th gear rattling under load at least that I could hear.

Your diagnoses?!

 

Does the intermediate gear in the transfer case spin when in neutral? Not that familiar with the Dana 18, so asking. If it does, it's spinning fastest in top gear. For the transmission, in top gear the input shaft is locked to the main shaft, so the cluster gear freewheels. You would think this would be the quietest gear for the transmission, not loud. Could be it relieves the load on the front main bearing and then it's noisy.

You could think about this in either of two ways. First you could think of the main things that go wrong with manual transmissions and the Dana 18 transfer case, and see if the symptoms match any of these. Or, you could think of the symptoms and, picturing how the transmission and transfer case function, imagine how these units could only make these

 

The output gear on the transmission in the boys made noise in third before it lunched his was abused. He has a three speed so third is like fourth.

 

From the Novak site:

"Because the Dana 18 is a side-drive type transfer case, the intermediate gear is under not only constant spin, but constant load."

But this doesn't speak to what happens when the TC is in neutral.

 

The bull gear can’t disengage from the intermediate gear, so if the transmission output is spinning, the intermediate gear in the t-case is spinning.

 

Straight cut gears tend to whine don't they?

 

Yes. That's why reverse has a characteristic whine in most transmissions. The more angle (helical), the quieter the gear but also weaker.

 

I agree. The SM465 doesn't make noise.

This is transfer case noise up close.