Check for the presence of a hydraulic suspension -- I don't know if it was an option or not.
If you have accumulators down there, and hydraulic lines to the "shocks" at the top, check the hydraulic oil reservior under the hood, you may just be low.
If you have fluid, check to make sure the link between the sway bar in the rear and the level control valve is attached amd moves with the sway bar.
If you don't have the hydraulic suspension, you have a broken spring on both sides.
Or a couple full barrels of beer in the trunk......
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!