Mercedes® Brake Vacuum Pump, 1977-1980 (116)

The first thing to check when you are having vacuum problems is the output of the vacuum pump. With either the diaphragm or piston type pump, the unit should produce 20 to 25 inches of vacuum at idle with all other consumers plugged off. If youre not getting a minimum of 18 inches of vacuum, the pump needs to be rebuilt or replaced. Generally speaking, if the case of the pump is cracked, or any of the internal metal pieces are broken the pump is non-repairable and needs to be replaced