1981 K5 Drivetrain shake/whine on freeway

[four50NCalif]

I get a shake/whine on the freeway between being on the gas on, off so basically when trying to cruise with little to no load on the drivetrain. When it does tighten up (on/off) the gas is fine, what is causing this? My thoughts are either the transfer case output shaft bearing, or my driveshaft is too short for my lift? Any help is appreciated thanks!

 

[GWeakland620]

What's your setup?

How much lift?

 

[Phil513]

I get the same thing, a weird hum when the driveshaft is in "float" mode. Like when I push in the clutch.

I have a 4" lift, dunno what the OP has. I'm curious for any suggestions too though. I just figured i need to go through the U joints.

 

[GWeakland620]

This is a common issue for k5's that have a 4in lift, but the stock shaft. I had the same noise when I first did mine. The quick cure, is to swap the spacer for the bolts on the cross member between the x-member and the frame. Thereby lowering the t-case 1"

 

[Carcinogen]

Might want to check your u-joints for slop also

 

[four50NCalif]

I have checked and greased the u joints they seem good, there is a very small wiggle to the drive shaft where it comes out of the transfer case. I am going to try to lower to t-case a bit and see if it goes away I will post results when I figure it out!

 

[92yamaha]

So, I've experienced the exact thing in my 84 K10. Any time I'm in between acceleration and deceleration, I got a horrible vibration and noise. I had slop in my output shaft, but the u-joints looked good. I HIGHLY suggest replacing the output shaft bearing, seal, and bushing. I haven't completed the project (apparently no one stock the bearing).

Here's a picture of my damaged bushing (apparently from a botched seal removal from years ago):

Also, here's a YouTube video I posted specifically for this thread. The bearing doesn't have much slop, but this certainly explains the noise I'm experiencing.
https://youtu.be/43nJ8IKSIzI

The bearing is PN: 6207, 207, 1207l, 607 (or some variant). You need to buy the output shaft seal KIT (comes with the bushing). PN: 1207l, 2607j, or 5208.

I haven't finished the job, but I'm sure this was the culprit. Hope it helps.