Booster Testing

[rmmagow]

Forgive me for asking this without checking the car first but I will not have inet access over the weekend (yippee !!!) Car's an 83 300D. I need to test the ability of my brake booster to hold vacuum. I have a Mityvac still in its box. What do I hook to? Once I see vacuum is being pulled and shut off the engine, should vacuum be maintained for a bit or drop right to zero. There's some o-ring that might need replacing, is this between the master cyl and the booster can? At 204K miles I may just spring for a new MC anyway but I want to make sure the booster unit is OK too. The pedal which is low to begin with, will drop as more and more pressure is applied, a common Master cylinder issue. No Leaks, no low fluid.
Thanks Much.

[Ralph69220d]

I'd first try bleeding the master cylinder, then see what you have. If still soft and compressible I'd bleed the wheel cylinders. Then if you still have soft brakes it might be the MC.