(With the Chassis resting on the suspension/subframe in "Road Ready" state.
To prevent "Preloading" of the Bushings. Disclaimer,My Interpretation!)

FSM's exact wording:
"Only tighten Hexagon Nut when rear axle is Horizontal."

(Now HTF are we suppossed to achieve that without the kind of lift that raises
the Chassis By The Wheels???)

I'm a thinking,Front wheels on Ramps...
Jack the rear up (using rubber jack points) High enough to insert another set
of Rhino Ramps underneath the rear wheels,and Maybe have enough wiggle room to get in there and wrench?

GSXR(Dave) did this on his garage floor (Without a Lift) so we know it's doable.

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'84 300SD sold
124.128