Packard Forum Index » Post-War (1946-54)

Hello everyone. It has been a some what long road , as I am just about ready to crank over the 359. Just tinkering with small things like plug wires and such. Well, I'm kinda embarrassed about asking but, there is 2 lines going to the, what I call, vacuum pump on top of the fuel pump. Which line goes where?? I'm guessing the windshield wiper line goes on in, and the line running up to the carb is your out. I forgot to mark them. Thanks,Brian.

Back to basics; just hold your finger over one or both of the two ports while you crank the engine over a few turns, even by hand if needed. The one that sucks air goes to the wiper motor, the other to the intake manifold.

Owen, I understand the suck port for the wipers, but if the other port blows air, what is the purpose of blown air to the intake??? The fitting that goes from carb to distributor, is that vacuum?? Also, the air line that goes to the tank and brake, how does that work. Thanks, Brian.

You are asking about 3 different systems. In a nutshell and over-simplified...

The power brake booster operates on engine vacuum. The system starts at the intake manifold as a source of vacuum, and is also equipped with a check valve so that if the engine stalls, you have enough vacuum stored in the reserve tank for 1 or more power applications.

The vacuum line to the distributor from the carburetor is for the vacuum advance mechanism which alters ignition timing based on manifold vacuum. For example, under periods of hard acceleration the manifold vacuum drops very significantly and the vacuum mechanism on the distributor makes an appropriate adjustment to the timing.

The vacuum wipers will ordinarily operate on the vacuum within the intake manifold, that is, it draws air from the wiper motor into the intake manifold. When under hard acceleration, the intake manifold vacuum will drop to where it isn't sufficient to operate the wipers and in that situation the vacuum pump which is part of the fuel pump will provide the vacuum for the wipers.

In the case of the wipers and power brakes, any trivial amount of "air" expelled into the intake manifold mixes with air from the air filter to provide the air/fuel mixture needed for combustion.

And doing Owen's explanation one step more as to why the pump operates when it does, the vacuum pump has valves constructed in such a way that under normal operation and high manifold vacuum conditions, just makes the pump act like another length of tubing for the vacuum going to wipers. Only when manifold vacuum drops or is completely absent do the springs operating the valves have enough strength to close the valves so pump can start to work.

Owen - 1948 with 288 engine. You are not saying there should be TWO vacuum lines going to the wipers ? The only one I have on my car is the one that goes thru the fuel pump and on to the wipers . Thanks

You are not saying there should be TWO vacuum lines going to the wipers ? The only one I have on my car is the one that goes thru the fuel pump and on to the wipers

Correct, I am NOT saying that. One vacuum line from the booster pump to the wiper motor, the other side of the booster pump goes to the intake manifold.