For starters 4x4 is not designed for hard paved surfaces. Any varaiation in tire wear meaning if back tires are worn from burnouts can cause damage as the shafts are trying to turn at diffrent speeds this is bad. But anyway there are litterally so many things that can cause that.

Ujoint in axle
Ujoints in drive shafts
tire variations
hubs
ball joints
tie rod ends
basicall any loose parts can possible cause this

take it to a field or some grass put in 4x4 on the grass and see what it does.

 

X2

 

X3

For starters 4x4 is not designed for hard paved surfaces.

Read your owners manual!

 

more info

I guess I should have given more info. We had a snow storm the other day, hence driving on the road in 4wd, felt a vibration thought it was from the bad plow job, also went hunting used 4wd down snow covered dirt road. To much snow and bumps on dirt road to feel anything. The only reason I was in 4wd on clear pavement was to verify weather the shake/vibrations was from the the snow and bad plowing from the city or my truck.
The 4wd works great just has the bad vibe. The tire wear is equal and even.
I checked the transfer case drive shaft there is no play in the ujoint and it turns freely.
The pinion is tight with no play in it either.
I do have a lift, diesel coils and 5 inch leveling kit from top gun customz, giving it an level 8 inches of lift and also a 3 inch body lift.
The angle of the front drive shaft is not to much for the ujoint.
I checked the vacuum lines completely and they are good.(obviously because the 4wd is working correctly but checked anyway)
The truck goes down the road straight without holding wheel.
I will jack it up and see if I can feel anything in the axle joints.

 

I guess I should have given more info. We had a snow storm the other day, hence driving on the road in 4wd, felt a vibration thought it was from the bad plow job, also went hunting used 4wd down snow covered dirt road. To much snow and bumps on dirt road to feel anything. The only reason I was in 4wd on clear pavement was to verify weather the shake/vibrations was from the the snow and bad plowing from the city or my truck.
The 4wd works great just has the bad vibe. The tire wear is equal and even.
I checked the transfer case drive shaft there is no play in the ujoint and it turns freely.
The pinion is tight with no play in it either.
I do have a lift, diesel coils and 5 inch leveling kit from top gun customz, giving it an level 8 inches of lift and also a 3 inch body lift.
The angle of the front drive shaft is not to much for the ujoint.
I checked the vacuum lines completely and they are good.(obviously because the 4wd is working correctly but checked anyway)
The truck goes down the road straight without holding wheel.
I will jack it up and see if I can feel anything in the axle joints.

You have electronic 4wd?

I know on some back roads in my area road graders are used with the huge knobby tires. If the traffic is light and it gets colder throughout the day/evening the tire tread in the snow hardens and acts like a washboard road.

 

NO i have manual shift 4wd. The road that I drove on to verify if it was my truck or not was a clear, dry nice paved road with no bumps. The vibe is really noticeable at around 5- 10 mph, and i never went any faster then that.

 

My guess....and it's a fairly educated one, is that your double cardian CV joint ball/socket assembly in your front drive shaft is starting to get some play in it.
I read that you checked your front shaft, but the double cardian ball socket is another matter.
It's a oft forgotten grease point and nearly impossible to see or get at without removing the front shaft. But it will set up a vibration when 4wd is engaged on pretty much any surface.
There's a quick easy test for this. Crawl under the truck (safety first) with it chocked and blocked, in park with e-brake set. The grasp the front shaft about in the middle and shake it. Don't try and turn it I mean rock it, side to side, up and down, and see any play or looseness in the big U-joint up by the transfer case. Any lateral motion at all is cause for concern.
If there seems to be a minute amount of play, you could try taking off the joint at the front pinion. With a helper in the truck to put the transfer case in neutral (with thier foot on the brake) rotate the front shaft and see if you can find the grease hole. It's about an 1/8 inch or less in diameter. If you can tie up the shaft, get a syringe fitting for your grease gun and force some grease in there. When it comes out the ball fitting on the shaft it's good. Assembly is the opposite.

 

Just did all u-joints this past weekend. Rear shaft went pretty smooth, the front one...... what a PIA. Turns out, original u-joints. Finally got all pressed out and def. changed out D-Cardan ball, spring etc. What a huge difference it's made!! Used to get a high speed vibration @ 50 mph, now smooth as silk.

 

can anyone get picts of greasing the cardan joint up? please?

 

x2

 

thanks for all the info,
I looked further into the problem. I have come to think that the transfer case is broke. I went to shift into 4l and there was nothing, the linkage was moving but not engaging. I only had 4h, and I put it back into 4h and creeped along quietly and heard the gears in the transfer case.

 

Ok did you get underneath the truck and determine this are you sure the front axle is engaging?

 

yes i did i ca move the shifter from 2h to 4l with no engaging

 

There's actually a chain in your transfercase...but if you heard grinding or crunching that's another matter.
Transfer cases don't just "break". They have to be abused...but there is a weak spot.
Inside the rear output shaft housing is a snap ring that holds the rear shaft output bearing in place. If that snap-ring were to snap the T-case would attempt to disembowel itself in a matter of minutes. That can happen but it's rare in a stocker. Still, it's easy to check out.
Pull the rear shaft (after securing the truck!) and take out the 4 bolts holding the output case to the main body. There's a bushing is on the main shaft so it slides with some effort.
That snap ring is either there, or it isn't. If half the t-case wants to come out with the output housing you are screwed.
Maybe a shift dog broke...still...thats pretty rare.

 

there is not any grinding or crushing noise, i do here the gears turning though, all most like they are not totally engaged into each other, i know there are some pads of some sort on the shift fork, I hope that they just wore out. There is no leaking, and no cracks anywhere on the case, I would tend to think that if the belt was wore out or broke then I would not have 4h I will post what I find when I do get it out and apart. One question I would like to know, where would be a good place to buy the replacement parts, I can repair kits on ebay, but they are bearing kits. I have a NP 231 D.
Thanks for the help and I will repost.

 

HAve you tested 4 lo? I was getting x-fer chain slap (Well it's a grind) Before it started jumping teeth and was removed to replace chain. It never felt like a washboard road though.

 

Just wondering if all your tires are the same brand. Tire diameter can vary between brands. I done the two tire buy on a truck,tried the four wheel drive on the highway about 40mph or so. Thought I'd murdered the poor girl. Had to pull off into the soft shoulder and back up to release the four wheel drive. Found there was close to an inch difference in the new tires compared to the old good shape ones that I had kept. Wasn't long before I replaced the other two and ended my troubles.

 

Hate to say it but dry pavement driving in 4HI won't do anyone any good. Even with the same height tires all around the axles will still bind with even very slight steering wheel movements. I prefer the full time AWD myself as it makes bad weather driving rather effortless and I use 4HI lock only on the trails. I ran 30" tires in the front and two 31.6" tires on the back that I had borrowed for a couple weeks until the new 30" tires came in. The AWD is more susceptible to hop than a part time system in 2wd where the front axle is disengaged and I didn't notice anything. I aired the rear tires down to 20psi just to get similar tire height and all was good.