Re: Stewart's 1955 Packard 400

Posted by Owen_Dyneto On 2020/6/17 19:59:28

That's a one-way or check valve for the vacuum brake booster. It permits the brake system to retain some vacuum after the engine shuts off so that in the case of an engine stall while the car is in motion, you still have enough residual vacuum for one or two powered brake applications.

The hose would run to the brake booster unit and on to the vacuum reserve tank located in the inner front left fender well. Browse the parts list for an illustration of the system.