We are in the process of swapping engines in my daughter's '91 240. While the engine was is out, we were doing a brake job. After installing the new pads & rotors, we were trying to seat the new pads by pumping the brake pedal. As you press the brake pedal, a low groaning noise was coming out the vacuum hose still connected to the brake booster and the pedal would go lower than usual.

Now I've never tried pumping the brakes with the booster vacuum hose disconnected so I wasn't sure if this is normal behavior. The FAQ here says to test the booster with the engine off and then start the engine to see if the pedal goes down further. Since I don't have an engine in the car, this is kinda hard to do.

Anyone out there able to tell me if this is normal behavior?

By the way, I checked the check valve on the booster and it seems Ok since air passes through it one way. Also, if I held my thumb over the hose and my son pumped the brakes, they seemed to work normally as far as pedal firmness goes.

Any help would be greatly appreciated.