Vacuum Coming Through Vent Behind Seat (Hydrovac Questio

[prairieplow07]

I have a 1962 GMC with a hydrovac brake system. Is there supposed to be vacuum coming through the breather behind the (drivers side) seat? I have vacuum through the breather during normal driving without braking. The brakes do work great.

 

[Longknife]

(quoted from post at 03:06:43 02/13/23) I have a 1962 GMC with a hydrovac brake system. Is there supposed to be vacuum coming through the breather behind the (drivers side) seat? I have vacuum through the breather during normal driving without braking. The brakes do work great.[/quot

I believe that should just be the exhaust when you let off the brake pedal . If vacuum is coming through when running with no pedal pressure it is a leak.

 

[wore out]

The hydrovac has failed internally, likely a hole in the diaphragm.