4wd seems to make a funny noise if i get going beyond 55mph. Like I'm riding on the rumble strip. Anything else, runs just fine.

 

You may recall i had to repair the shaft got a used one then redid the u joints on that. Could it be out of balance?

Are you locked in 4 hi when this happens?

 

will it do it in 2wd?

 

my guess is if you got a used one or had to repair it that is probably your issue, If it is I would remove it before something catastrophic happens. broken driveshafts or u joints at hiway speeds usually don't turn out good.  If you remove the driveshaft and problem goes away then you defiantly need a new shaft, A rebuild by a driveline shop would be your best bet. 

 

Personaly if if your getting that much vibration at that speed I don't think balancing is going to help

Edited December 19, 20168 yr by 01cummins4ever

At this rate should have bought a new one from rock auto...

I had a similar issue with mine, it was the actuator failing to hold the collar back fully.  It would then grind on the outer shaft.

 

Easy way to test is pull it into 4wd when it happens.  Does the noise go away?  

So pull back on the 4wd shift selector while in 4wd?

I guess since yours does it in 4wd I would do the reverse and see if maybe the collar is not strong enough to hold 4wd.  

 

Go from 4wd to 2wd and see if it goes away.  

 

I also noticed that if the  tailhousing shaft bearing is loose the entire shaft can move back and cause the synro to grind in the transfer case.