When i have conect the Front drive shuft i have vibration after 50miles. When i disconect it the vibration stops. I check the shuft align and its good. I have 3" lift and 3/4" TC drop.
I must have 1" TC drop?

 

Sounds like you have a bad universal joint or CV joint on your front Drive shaft. Whenever you put torque to it, it starts vibrating.

 

x2 Check those U-joints.

 

what year is the jeep? if it is an older style with the gku (stick in a can) style make sure it is greased... had 300xxx on mine with out grease and it fell apart and would vibe real bad after a little driving... if it is a newer one check the ujoints like mentioned above

 

It also may be out of phase but it is unlikely unless it has been rebuilt.

 

my 91 did that with the TC drop
I got rid of the TC drop by adding a cv type shaft in back
now Im good to go

 

I have the exact same thing at 65 mph on a completely stock 96 cherokee. I replaced the harmonic balancer, ALL universal joints, and had both shafts balance checked and trued. Still... RUMBLE!

When I took the front shaft out and drove it, the rumble was gone. It drove nice.

I think the problem is just a matter of over-driving the mechanics of the design. If you could just unlock the front hubs, you wouldn't have to push all that energy through, from the turning of the wheels all the way through the transfer case.

Just my thoughts. I've pondered this for quite some time.

 

hit the ds with some grease.