I just got an 85 Vanagon.  The brakes would take 3 pumps to pump up, so I replaced the master cylinder.  After I replaced it, I bleed the brakes.  Now when I push the brakes, I hear a hissing noise coming from the booster and still takes one pump to get a firm.  I pumped the brakes and held them down with the engine off, and when I turned the engine on the pedal depresses slightly and holds (bently test). When I turn the engine off, the hissing stops from the booster (holding the pedal down).  When I press the brake the rpms on the engine go up. I should also mention before I changed the cylinder and before I bleed the brakes, I did not notice the hissing sound.  The rotors, pads, drums, shoes, etc. are good and there is no break fluid leaking.  I would like to solve this tommorow.

Does this mean the booster is bad?  Or is it a vacum leak somewhere?  Could I have hit a vacum line or something when I changed the MC?  If it is a vacum leak, where/how do I go about finding it?  I have an 81 westy, is the booster the same as on a 85?

Thanks, 

Mike

85 Vanagon
81 Westy
72 Westy