Originally Posted by Oldwolf

Last night when I got home I took some vacuum measurements…
Hot Engine (all measurements - in Hg)
23 @ Vacuum pump
23 @ Non-Return valve

This morning I took measurements after starting the cold engine…
Cold Engine
23 @ Vacuum pump
23 @ Non-Return valve

Some other observations:

-When the vacuum gauge was attached to the shut off valve port on the Non-Return valve, and with the engine running, pumping the brake pedal would make the vacuum eventually rise to 10. After ceasing pumping the vacuum would drop back down to 23 again. Is this the correct vacuum pump capacity when at idle?

- Using a mechanics stethoscope on the vacuum pump, and with the engine running, I cannot hear any abnormal sounds coming from the vacuum pump.

This morning when I disconnected my shut off valve port / hose connection, I could hear air sucking into the port. This seems to indicate the No-Return Valve is doing its job and that the brake booster diaphragm is not leaking.

But, driving down my street again this morning (after doing the pumping thing explained above), I lost power assist to the brakes for a few applications. It returned as it usually does.

Conclusions so far…
I am thinking my vacuum pump is OK unless one of you guys says otherwise. Now I need to test my brake booster. How do I do that?

Any other ideas?

Thanks for all your comments so far.