NV4500 Growling noise and worn bearings on fresh rebuild

[canadaboy25]

Hey everyone,
I apologize in advance for posting a question about a GM truck on a RAM fourm, but the transmission was used in a Dodge and the community seems very knowledgeable about these transmissions.

The transmission makes a fairly loud growling noise whenever it is lugging the engine. When I let off the clutch and start to move, I get a growl. I also get the growl when I up-shift early and the higher gear lugs the engine. As soon as I give it some throttle and accelerate, the noise goes away. It happens in all gears.

I picked up this transmission as a junk unit for free. It was completely destroyed when I got it. I ended up replacing the input shaft, main shaft, 3rd gear, 3/4 clutch/synchro hub, and every bearing and synchro. The only bearing that was not changed was the needle bearing inside 5th gear since it was out of stock and mine looked perfect. I followed the manual exactly, and also verified the order and orientation of all parts using the exploded diagram. I set the end play on the shafts using a dial indicator and torqued everything to spec. I am 100% confident I assembled eveything as I was meant to.

I installed this transmission to replace the SM465 I had in the truck. The engine, flywheel, clutch, pressure plate, and transfer case have not been modified since the swap, so I am confident they are not causing the noise. The noise has been there since the very first time I test drove the truck after the swap.

I've uploaded 2 videos of it making the noise. You can very clearly hear it in the first video, and you can hear the abrupt starts and stops as I press and release the clutch about half way through the video. The second video you can hear it really loudly as I shift into second gear.

I made a 4 hr round trip with the truck, and found a few more details. Growling noise at low RPM's is still there. However, I am now able to hear the noise in 5th when letting off or stepping on the throttle.
After the trip, I decided to check the oil for metal. Pulled the fill plug and the little bit that came out had fine silver particles in it. There's no way I can drive it like this so I decided to pull it and tear it down. Draining the oil into a funnel reveled that there is a LOT of metal in the oil.

Got the trans tore apart and did not find a clear indication of a problem. All needle bearings and gears look PERFECT. The only thing I found is that all of the tapered roller bearings look scored. I've attached pictures of the input shaft and mainshaft bearings/races. This kind of scratching does not look like normal bearing wear to me and has to be the source of the metal. Everything else looks perfect. The transmission only has about 300km on it so this wear on the bearings and races looks kind of extreme to me. I cannot catch any of the scratches in the pictures with a finger nail, but they were brand new bearings 300km ago...

The countershaft looks about the same, but to a lesser degree. I rechecked the endplay with a dial indicator and it is about 3 thousandths. I also checked the pilot bearing in the flywheel and all seems well. I have no idea what else to check as everything looks perfect except the tapered roller bearings, and I have no idea what is causing them to fail.

Any ideas are welcome.

https://youtube.com/shorts/eVgKd5aUbLQ
https://youtube.com/shorts/OcT9Ko9QU5A

 

[SAndreasen]

Contaminated oil will scar bearings like that . As far as the noise do the gears have any scoring or marking like the bearings had. I like to set the end play at 1 or 2 thousandths they are more noisy the more endplay you have

 

[BigPapa]

Every manual I've ever been in sounds like that when lugging the engine. Don't do that. You're transferring destructive harmonic vibrations from the engine to the transmission.

I've ridden with several fellows that evidently think it's cool to be in 4th at 30mph. I don't understand. I've never lugged an engine and I've instructed both my kids who drive manuals to never lug it. My son has a Mustang GT and my daughter has a V6 Ranger (I know, I know, I screwed up somewhere and raised kids that like FORDS...). If they get below 2K rpm, they downshift.

 

[Topzide]

Find that sweet spot on the tach where it just sounds right! You'll know it when you find it. Keep the rpm's up until you're at cruising speed, then grab higher gear and settle in to keep the speed! Sometimes I miss my little Toyota 4x4 with the 22R carb with 5 spd. Can't hold a candle to these trucks through!
Back on subject; was truck ever driven through high standing water? Hot manuals tend to draw water in. Other thing is you need to drive truck to get trans up to temp just like engine for changing the oil. Cold drain leaves a lot of old oil in it. Hope you can get it sorted out!

 

[Ozymandias]

Every manual I've ever been in sounds like that when lugging the engine. Don't do that. You're transferring destructive harmonic vibrations from the engine to the transmission.

I've ridden with several fellows that evidently think it's cool to be in 4th at 30mph. I don't understand. I've never lugged an engine and I've instructed both my kids who drive manuals to never lug it. My son has a Mustang GT and my daughter has a V6 Ranger (I know, I know, I screwed up somewhere and raised kids that like FORDS...). If they get below 2K rpm, they downshift.

With Gas engines one doesn't need to care for this, it's the Diesel that hammers the gears to ground.
Apparently the transmissions are not up to the task to stand behind that engine.
As soon as it goes commercial it needs to be foolproof, no way around that or it will end costly for the employer.
Through all my driving career I never had a vehicle where I needed to watch for trannys well being aside from keeping it full of oil.

As a side note, driving school for cars in Switzerland demand that you are in highest gear at 35mph cruising down the road. Not in that gear? Fail the test.