The spacer fits immediately above the steady bearing bracket. On mine it's exactly 1/2".

I'll look in the morning for the tapered shims you mentioned and let you know right away.
I can sympathise here, I have a shudder that starts at about ohhh... 62 kph and runs up thru 72/73 kph. After that it's good till about 110 kph and it starts again. At 120 kph no problem and its ok up to 165 kph.... yaa I know, don't ask... it was quite the ride....

Pastor Bob.

 

I lowered my center bearing by placing a Lug Nut between the frame and center bearing mount. They were about 1/2" thick so it worked rather well. It did seem to work for me as I have less vibration.

 

I called the DC dealer and gave the parts guy the number (4746012), he told me they didn't have it but it can be ordered. The price was $300 or so. I don't remember the exact price - shock kinda affects my memory!
I went to a local welder and bought some 1/2" X 2" stock to make a shim - payed him $10 for his trouble instead of $5.
Hope to have it in this afternoon.

Chris

 

Installed my homegrown center bearing shim and so far it has helped. I haven't had the time to find a real steep road to test it, but so far so good.
Also changed the rear diff. gear oil with Valvoline 85w-140 and Mopar additive - chatter gone - for now.