Diagnosing mysterious sound from Tran/Tcase

[chief_shotts]

The truck is a 1987 crew cab k30. 383 stroker, turbo 400, np205, d60, gm14bolt. The issue is Ive been experiencing some vibration at 3000+ rpm. I think it comes on sooner than that but the vibration becomes evident at higher rpms. The vibration feels like it is coming from a rotating assembly because of the way it surges and increases with the speed of the engine. Id also note there is a odd sound that accompanies the vibration. Something like a out of balance washing machine with marbles in it but very subtle... hopefully that makes sense... its not a grinding noise exactly but its not not a grinding noise...

The engine, trans, and tcase are fairly new (couple thousand miles) all rebuilt by a reputable shops. The rear end/ front end are also rebuilt. The front driveshaft is being rebuilt as we speak and the rear driveshaft was rebuilt, balanced, phased.

I thought maybe it was the driveline angles on the rear end. I adjusted so that the rear pinion angle was parallel or close to Parallel with the tcase output. This had zero effect.

I removed both driveshafts and revved the engine in gear while parked in the driveway... I could still feel the vibration and hear the noise.

I have the ability to remove the floor over the trans tunnel.. so i did.. and with the trans in nuetral and the transfer case in gear i spun the output yoke and this when i discovered a strange noise coming from the transmission that is very similar in nature to the sound i hear at high speeds (sounds like theres marbles in the trans)+ a whining noise. Please watch the video attached and listen for yourself. Does this seem odd to you guys. Could there be something wrong in the transmission and that is what is causing the vibes.

I'm leaning towards bringing the truck in to the trans shop to have them look it over. But I am a bit weary of going to the same shop as they built it to begin with and Ive put very little load/ miles on the trans since rebuilding it.

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[Turbo4whl]

Check the trans torque converter bolts that mount it to the flex plate. They sometimes come loose.

 

[Chevy 88]

I don't see anything in the video that could be causing this. Maybe that linage needs to be adjusted?

(click on pic)

 

[chief_shotts]

Check the trans torque converter bolts that mount it to the flex plate. They sometimes come loose.

Ill double check right now.

 

[chief_shotts]

I don't see anything in the video that could be causing this. Maybe that linage needs to be adjusted?

(click on pic)

Sound/ vibes existed before and after that linkage was installed. Were you able to hear the noises from the trans in that video?

 

[Chevy 88]

Sound/ vibes existed before and after that linkage was installed. Were you able to hear the noises from the trans in that video?

Click on the image, and then take a close look at the bolts.

 

[chief_shotts]

Click on the image, and then take a close look at the bolts.

Im not following.. What's wrong with the bolts?

 

[chief_shotts]

Check the trans torque converter bolts that mount it to the flex plate. They sometimes come loose.

I checked em... one was not as tight as the other two by maybe a 1/8 of a turn or less but that was about it. Definitely not lose

 

[chief_shotts]

Ill try to capture a video of the vibe/sound while driving with the trans tunnel exposed. should be noisy/hot test drive

 

[chief_shotts]

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The noise is subtle in the video... sounds like a rattle noise that sort of pulsates.
comes on at about 5 sec mark then fades at 10 sec mark. then comes back aroud 20-25 sec mark

 

[77Dmax]

You can unbolt the converter from the flexplate and start it up. That'll point you in the right direction.

 

[chief_shotts]

You can unbolt the converter from the flexplate and start it up. That'll point you in the right direction.

thanks for the idea. Should help me narrow it down.

 

[Chevy 88]

Is there glitter in the trans fluid?

 

[chief_shotts]

Is there glitter in the trans fluid?

Not when i check the dip stick... but i haven't dropped the pan yet.

 

[chief_shotts]

So I took it to two separate shops. One says it's the transfer case for sure. The other says it's a wheel/driveline vibration.

I've adjusted the driveline angles in various configurations and it was made zero impact on the vibration and noise. It still makes the exact same pulsating vibration/ rattle. I just had the wheels balanced again and this also had no effect. I suppose still the driveline angles are not absolutely perfect and could be the culprit but I'm not buying that. Maybe somebody could pitch in and tell me the perfect setup for driveline angles on a two piece rear driveline. It was my understanding the first driveshaft after the transfer case is to be treated as an extension of the drivetrain with an approx 1* ish difference from transfer case to ensure u joint lubrication. Then the second shaft is treated as any normal driveshaft....with equal operating angles on each end/ parallel angles of pinion and carrier bearing joint. Also all joint are in faze.

I would also note that I have isolated the noise to a specific road speed (75ish mph) and not an rpm. In 3rd gear noise occurs at 75mp/ 3000k rpm. In 2nd gear the noise occurs at 75mph/ 4500krpm. Correct me if I'm mistaken but I think this clearly indicates the noise is not coming from the engine/ torque converter/ or transmission?

My gut feeling is the transfer case.. because it sounds like wonky bearing rattling in the transfer case and the vibration is felt thru the shift linkage. With that being said I've dropped the oil out twice in the last month or two and it's totaly clean. Could the transfer case still be the culprit and just not showing any signs in the oil?