1950s 1957 Limo Rochester Vacuum Port

[Kurt Kjelgaard]

Hi everyone,

Getting my 57 Series 7533 back together I have a question about a vacuum port in the intake manifold.

The carburetor is boltet down on four studs with a washer and a nut.
The rearmost drivers side stud on my car is hollow to allow vacuum from the manifold to be used somewhere.

The size of the protruding pipe is for a fairly small diameter rubber hose.

For info, the engine has the standard oilpump/vacuumpump combination and the wiper system is connected to the pipe coming up on the engines right side from the fitting in the block.

Anyone seen this before? If so, what is it connected to?

Kurt
 

[D. Mailan]

Yes, I have seen this before.

GM offered a pcv valve conversion kit that recirculated the blow by from the crank case tube. To make this work, the Bakelite heat insulator would be replaced with one that has a fitting for a pcv valve.

The issue being that the location of it did not allow for the manifold vacuum line that goes to the wiper vacuum block to remain in place. (It would not fit.) 

To remedy the issue, the vacuum line on the top of the intake is capped off. And they removed one of the rear studs for the carburetor and installed a hollow one to provide vacuum to the wiper block. My 1958 Cadillac has this set up. It is an oil crisis era dealer/mechanic kit. Its all GM products. It is possible at one time your Cadillac had a pcv valve system and it was removed and put back to its original setup. 

If you have a picture of it that will be great. I will see if I can get a picture of mine so you can see what I am describing.

[D. Mailan]

Here are some photos from my 58

[Kurt Kjelgaard]

Excellent, thanks - my 57 has the conversion kit just like yours. But as I understand it, the vacuum for the wiper system should come from the internal vacuum pump directly, or? This to avoid wipers to slow down during acceleration, such as during overtaking. So what is connected to your internal vacuum pump?

[D. Mailan]

Cadillacs with the vacuum wiper motors and washers have a "manifold" located on the firewall. It is important that this manifold is working properly. As well as the check valve located on the side of your engine block where the vacuum pump line comes out.

The vacuum pump does not generate much if at all any vacuum at idle and low rpm speeds. It is used for high rpm vacuuming to compensate for the low vacuum from the intake manifold. The firewall manifold joins these two together to provide appropriate vacuum for the wipers. There are some problems.

The vacuum pump is located below the distributer submerged in oil. To prevent the oil from being sucked into the intake manifold, there is a check valve located near your starter. It is where the vacuum pump line exits the engine block. If that check valve is stuck open, in many cases it is, when you are idling, oil that the vacuum pump is submerged in will be sucked into your intake due to the stronger vacuum source. I have watched it happen by placing a clear tube in between the vacuum pump and the vacuum manifold on the firewall and seeing oil going strait to the intake.

My vacuum pump works well but unfortunately the check valve doesn't, you can get a vacuum check valve from the auto store to remedy the issue. I didn't do that since the California weather doesn't require many days of wiper usage. I simple connected my vacuum line that comes from the manifold to the hollow carburetor stud. It works well once you get up to speed. Yes, when overtaking or accelerating, they slow down but not significantly.

I would also recommend a vacuum tank could also help.

Hope all this makes sense, there are many forum topics that address vacuum wiper schematics.

[Kurt Kjelgaard]

Good explanation - thanks.

However I am a bit confused about this:  "I simply connected my vacuum line that comes from the manifold to the hollow carburetor stud."

Comes from where on the manifold?

As you can see from the picture attached, vacuum for the brake booster comes from the connection in front of the carburetor.
The vacuum port on the rear of the throttle body is source for the fast idle speed-up control (car has a/c). The vacuum port on the right side of the throttle body is connected to the distributer advance.
This leaves just two vacuum sources - engine vacuum pump and manifold hollow stud.
Is the wiper system is connected to both? If so, how?

[D. Mailan]

Kurt,
Yes, the vacuum wipers are connected to both, the vacuum pump from the engine to provide vacuum during acceleration, and the "hollow stud" which provides vacuum during low rpm. They are joined together with a aluminum block also known as the vacuum manifold.

https://forums.cadillaclasalleclub.org/index.php?topic=108350.0
https://forums.cadillaclasalleclub.org/index.php?topic=109217.msg154841#msg154841

Here are two forum posts that I recommend to look at to fully understand how the wiper system operates. There are great detailed images and info provided by many great minds who probably would explain it better than I.

Hope this helps!
Derick

[Kurt Kjelgaard]

Derick, thank you so much - now I get it......
Kurt