It is also possible that the booster is leaking down while you have the pedal depressed, giving you a VERY hard pedal. If it doesn't sink, just gets very hard, booster. If it sinks slowly, master cylinder.

I have to use tremendous pressure to stop mine (in the 50 yards or so I've driven it) mainly due to rust on the rotors, I think. I have a rebuild kit for the master cylinder, as mine was leaking out the weep hole at the rear bottom side (and there is no paint on the bottom half of the booster). Will do that and bleed, probably pull the wheels and check pads, too, once I get the engine to hold water.

The vac hose can be bad, too -- they get hard and brittle with age. Ditto for the check valve.

Vac leak should give you a racing engine, too, as this one will add fuel rather than go lean, so maybe you have the engine pulling you , too!

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!