Your vaccuum pump should produce at least 12" vacuum after a few minutes of running.

If you have vacuum, either the vacuum switch on the key switch is bad or the cutoff solenoid is bad. You can check with a vacuum pump.

The supply for the cutoff is a brown hard plastic hose going into the passenger compartment from the main vacuum line (that goes to the booster). The operating line is brown with a blue stripe.

You can do a quickie test of the solenoid by disconnecting the vacuum line, pushing the stop lever down, putting your finger over the fitting, and let up the lever. If the lever moves at all, other than very slightly, or creeps up slowly, it is shot. Otherwise, you either have no vacuum supply (plugged or leaking brown line, bad vacuum pump) or the switch is bad. If you have vacuum, the cutoff is good, and no shutoff, the switch is bad.

The usual problem is that the rubber connectors for the hard plastic lines go bad and leak, easy to fix.

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!