Hi, Just got back from a 900 mile trip and have a intermitant harmonic vibration at 65 to 80 mph. It comes and goes in a as long as you are on the gas. It goes away when coasting. 2006, 4 x 4, Hemi, Cooper Discover HT Plus balanced in the spring. On the plus side I did get the best millage ever with this heavy pig at 18 mpg Canadian Gallon.

 

Sounds like driveshaft or ring/pinion. I would look at your driveshaft first and confirm your u-joints are tight and not loose.
Also, the rear diff fluid should be replaced every 30k miles at most! Much sooner if you regularly tow/haul. It uses 75w-140 Synthetic only.

 

Ya diffs fluids have been changed and were checked last week and are still clear, I know the u joint at the pinion is tight for sure.

 

I crawled under today and b

 

And both u joints are tight, and I know that they have both been replaced. However forgot to mention earlier that the truck only has 48000 miles on it.
I did notice that if you push up with some effort on the front yoke as it comes out of the transfer case it does move making a clicking sound when pushed up. Can anyone verify if this is normal. Thanks.

 

No it shouldn't have any movement in the output bearings. That is likely the issue. I just went through the same thing on one of my jeeps. I replaced the driveshaft, had it rebalanced new u-joints and all. The front output bearing was bad and that fixed all my vibrations.

 

The bearing does not appear to have any play but I would saw that it acts as the fulcrum of the sea saw like action when you push up on it. Is there two bearings one on the inner and one on the outer to keep the shaft from moving? Thanks for the responses thus far.

 

You shouldn't be able to budge that. At all! Think about how much torque is on that shaft when engaged in 4wd? Take it off and inspect it. I certainly wouldn't drive it until it's fixed. That or take the shaft out completely. You might leak a little fluid while driving though so put a spray bottle cap taped over the hole...lol j/k

 

Thanks so much for all of the response so far, especially Dirty dog, I myself try to contribute as often as possible but someone always beats me to the punch. I figure there is no point in saying the same thing again, yet others jump all over you for trying to help out.

Anyway here is the update, had it in at the dealer today and my tech did infect verify with me that there is infact play in the tail shaft of the transfer case which powers the main drive shaft to the rear wheels.
The service advisor that I have always dealt with is on holidays till next Monday, so I am returning then, to see if it can be put through under warranty which expired due to time last Friday!
The tech wants then to change the whole unit at a warranty cost of 2400$ plus about 500$ labour plus 13% sales tax.
If it is not going to be covered by warranty I am certainly going to have to go a different route.

 

Wow, that is an expensive repair. If they won't do it under warranty the bearing, seal and sleeve are around 40.00 and take a couple of hours to replace.