Can you hear the pump run?

If so, very likely you have a broken vacuum line, there is only one (vac to lock, pressure to unlock). If the pump does not run, you will have to check the wiring to it for power (the connector can come off). If it has power and does not run, replace it.

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!