No, the spring simply bends and goes "flat". Coil springs are more likely to do this than leaf springs, but their other characteristics more than make up for the sag problem.

Peter

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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!