The front DS on disco XJ's are not balanced from the factory

The 3 I've done were. Balancing weights on them and no vibes. All 3 are DDs.

hmm my 88 wasnt, had me chasing my tail for awhile and it didnt have marks were the weights were welded to it. something for the OP to look at.

Also I started getting vibes (different ds in a different XJ) as the ball/socket joint in the double cardigan joint was going out, shook the whole vehicle like a bucking horse when it finally failed on the highway.

Where does it get it's vacuum from I would like to fix it so that the vacuum disconnect works like it's meant to.

I've never gotten into mine to trace it. There must be a valve activated by the 4wd linkage somewhere. The valve might even be controlled electronically, but I doubt it. So there's that! (until someone else comes along) (the valve will get manifold vacuum from somewhere)

I found it! It's on the "front of the transfer case". See if the lines are disconnected/funky. See that one is getting vacuum.

Manifold to t-case switch to disco.