Brake trouble. '91 R129 What's your experience?

[tecqboy]

I'm having an issue with excessive brake pedal travel. ( '91 300SL 110K miles) So, I put on new pads front and rear. New rotors in front and new brake hoses in the front. When bleeding the lines by pumping the pedal, I get a firm pedal with short travel if the engine is not running ( No vacuum to booster ). But if I run the engine, the pedal is soft and drops to the floor with less than moderate pressure. All those new parts didn't help at all. Ordinarily, I'd suspect the master cyclinder, but with no vacuum, the pedal feel and travel seem normal. The car does stop, but not like it should. Anyone have any insights or suggestions? Why does the MC seem OK without vacuum? Thanks for any ideas. (Also posting this in the SL forum.)