Don:

You have either a leak or bad pump. One shot of power brakes with no boost until you drive for a while suggests a pump.

Does your vacuum pump still clatter? If not it is probably shot.

Vacuum systems on Volvos are pretty simple -- pump (on the side of the head, about the middle, can't miss it!), hose to brake booster and to AC controls, booster and AC unit. Cruise has it's own pump.

If you can get the lines off (ha, hard as rocks!), check three things :

1. does the pump generate and hold vaccuum? (use the trusty MitiVac!) It can be rebuilt rather easily, not a nice as the MB one (requires a vice to hold the diaphram spring down)

2. Does the check valve at the booster hold vacuum?

3. Does the booster hold vaccuum? (including the rubber seals, etc).

Remove and plug the AC hoses while checking the booster -- this will tell you if the leak is there instead.

it will take a while to pump the booster down with the Mitivac, but if you never make any progress, there is you problem. I've had several boosters die over the years -- gas engines are easier to diagnose as the idle goes funny when the booster leaks -- had the old Dodge die when I stepped on the brakes cold, for instance.

The other thing that can happen to the vacuum pump is for one of the two drive plungers to stick -- this is bad, as the body of the pump is aluminum and will therefore be nonrepairable.

Good luck!

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!