Noisy NV3500 - sounds like T/O bearing but it's not???

Please help me out here before I start throwing more parts at this transmission semi-blindly. The truck is a 1996 GMC with NV3500. A couple weeks ago, it started making a whining noise in neutral like throw-out bearings do when they go bad. When I would push in the clutch and wait a couple seconds for spin-down, the noise would go away. The noise is there with the transmission in neutral and in gear while the truck is moving. It was getting so loud that people stopped to stare while I drove through a parking structure last week.

I was so certain it was the throw-out bearing making the noise that I R&R'd the transmission on Saturday and installed a new T/O bearing. After about 6 hours of work, I started the truck back up and the noise was still there; changing the T/O bearing did not make the noise any better.

Does this sound like the transmission input shaft bearing? There seems to be excessive radial slop in the input shaft when I move it by hand, but I'm no transmission expert - it just seems like it has more play in it than it should. I removed the transmission again tonight and removed the input shaft bearing from the case. It spins freely but I can feel a little something in the bearing when I hold it on 2 fingers and spin it with my other hand but I don't feel any grit when I side load the bearing and turn it slowly. I'm not sure if the 'something' I feel is enough to make the "whah, whah, whah" sound the truck was making but I'm not loading the bearing or spinning it up at 700rpm like it does at idle in the truck.

The transmission was rebuilt a couple years ago and most of the internals (input shaft, counter shaft, bearings, etc) were all new. The transmission has about 40k miles on it since the rebuild.

I have been searching for an input shaft bearing and places that realize I'm not looking for a pilot bearing vary in cost from $75 (Car Quest) to >$110 (dealer). I can get an overhaul kit for the transmission with new bearings for a bit over $200.

Any ideas? Thanks for your thoughts...

T/O Bearing will normally make noise only when the clutch is depressed.
If the noise goes away with the clutch depressed this means that the offending part/parts has to be something that is turning when the clutch is engaged and the tranny is turning.
Very well could be an input shaft bearing. If it does it in neutral with the truck stopped and the clutch engaged then its almost certainly the input shaft bearing.

An observation here, if that bearing is gone I would be looking at all the bearings in the box when you get it out.

Also if its been a long time since things were apart I would replace the Pilot bearing too in the end of the crank.

Big job to get at it and if you have it apart again its not that much more work. Look at the clutch too and if its worn I would just do it too.

I see that you have the box apart now.
Look it over real good there has to be an explanation in there somewhere for the noise. (possibly gear issues) ????

I am not well versed on the NV 4500. Does the main shaft connect directly to the counter shaft via a gear? if so then the counter shaft could be the issue and not the input/main shaft.

Good luck

Robyn

Ok to answer my ?? to you and possible your issue. ( I dug out my book on the NV4500)
The input shaft is geared to the counter shaft up front via the main drive gear,
Very possibly one or both of the timken bearings on the C/S are toast.

Give it a look see.

Robyn

He asked about a 3500, but I doubt if it's any different.

Does the noise diminish in direct drive vs. a lower gear? If so, it's more likely the counter shaft.

If you coast in neutral, let the clutch out and shut off the engine, does the noise stop? How about if you depress the clutch with the trans in gear at a stop and the engine running?

If you can feel any roughness in a bearing, it's probably bad.

Was the oil level low? How much metal on the plug?

Take the bearings to a bearing distributor and have them match them up for you. Much cheaper...

Basic structure is about the same as the 4500.

Hmmm... Didn't know they put the 3500 behind diesels... It is pretty light duty.

99% positive it is a NV4500 unless someone has changed it out for some odd ball reason -- stock is NV4500. I sure hope you checked/changed the pilot bearing when you changed the throw out bearing. Check the input shaft (end where it goes into pilot bearing) for damage. Also replace the throw out lever & pivot ball if you have not already done so.

*Note* The chevy designate it as the MT8 or GMC MW3
Al