Dave:

Most likely you have either a leaking booster or a bad vacuum pump diaphram.

Check the vent line from the vacuum pump to the intake mainfold for oil -- if there is any significant oil in the line, the vacuum pump diaphram is shot.

How much vacuum do you have with the engine shut off? Can you apply the brakes three or four times before you lose boost, or is the pedal hard immediately? If you have no reserve vacuum in the booster, it is probably shot. I had one on my old Dodge Aries that leaked so badly the engine would stall when I applied the brakes!

If you have reserve vacuum, but never have enough in the line, check for leaks -- the lines get hard and loose on the fittings. If you don't find any, you probably need a new diaphram in the vacuum pump. This isn't a big deal.


Peter

__________________
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!