Vacuum Pressure

[JohnC]

Hi all,
Been a while since I posted...things are going pretty smooth. I have a question on the vacuum pressure from the pump. I did as the book says, disconnect both lines at the vacuum pump, connected the vacuum fitting to the wiper side of the vacuum pump and run the car. I get a steady 9". Is that enough? The book say 10" minimum? Second question, When I hook the other side of the pump back to the manifold, the pressure on the wiper side drops to about 4". Is this normal?

Thanks

[Barry Wolk]

A healthy ICE should produce 19-21 inches of vacuum. I installed a T in the vacuum tubing to check.

It sounds like you have massive vacuum leaks somewhere. Isolate the problem by taking the large vacuum line off the intake manifold and capping it. That takes the storage tank and the Treadle-Vac out of the equation. Cap off the vacuum line to the vacuum pump. That eliminates all of the ancillary items from the pump side, like washer and wiper, antenna and heating controls.

Once the engine is isolated from the rest of the car check the vacuum again. That's when you get your peak vacuum from air been sucked through the intake manifold.

Once the engine is running at peak vacuum the pump has something to work with and will supply steady-rate vacuum instead of the ups and downs of throttle effects.

Just before the vacuum supply line enters the cabin it T-s off to the wiper motor. It sounds like it has an operational leak. If the paddle inside the vacuum motor is worn it become a big vacuum leak. By capping off the feed to the wiper you can see by the gauge whether part of your problem is there. You could have a big vacuum leak in the washer bottle if the solenoid is stuck, or is gettin a constant signal to open the vacuum valve. You can further isolate the heating system, which uses a vacuum operated thermostat in the ductwork. If the Treadle-vac us not returning to its resting position the vacuum assist will always be on. If you've confused the vacuum antenna hoses you could be constantly calling for vacuum. And then there are the vacuum lines themselves. Vacuum pressure is a misnomer. Vacuum is a lack of air pressure. If you will, a negative air pressure. Pressure hoses like fuel and water are designed to keep the like from expanding while vacuum lines are thick-walled, designed to keep the lines from collapsing under negative air pressure. I've seen the mistake over and over rebuilding Treadle-Vacs. People replace the original vacuum line with water hose or fuel line and never see the mistake until the booster becomes ineffective. As a test you can squeeze the large line to the T-V while the engine is running and rev it, and let off the gas. The higher vacuum of deceleration with the throttle closed will egg-shape the line, or collapse it if the rubber is hot enough. I use a 1-wire hydraulic hose that won't collapse an normal engine vacuum. Look at your small hoses. If they are smooth they are not vacuum lines. They typically have ridges cast into the extruded vacuum lines so you can tell the difference.

Now you should throw away your timing light and tune the engine by vacuum. The timing marks become irrelevant with an old engine, so they should be used for only getting the engine close. With the engine warmed up turn the distributor until vacuum increases, Adjust the idle adjustment screws until the engine stumbles and back off until the engine runs smoothly. Now lower the rpm to about 500 and adjust the distributor again, trying to achieve peak vacuum. Through a series of adjustments you want to attain the lowest rpm at the highest vacuum. Take it out and see if you get pre-ignition knock. Simply retard the timing until the knock goes away and you have the best balance of air, fuel and spark.

Everyone that uses this method has seen marked improvement in performance and diminished exhaust smells.

[JohnC]

Wow Barry...Thanks...great info...so really I should have the whole vacuum circuit (loop) connected before I test from the vacuum pump again and then if my readings are wrong, run through this trouble shoot. i was under the impression that I could just test the vacuum pump without hooking the whole thing up. The 'T' you installed for the testing is on the washer vacuum line at the pump? i like that idea

[Barry Wolk]

You can simply isolate the pump to test it, but that's not likely your problem as your engine should be pulling full vacuum without it, it's just a booster. Everything vacuum will work without it.

This is where I placed the T. That's a straight tap to manifold vacuum.

https://hosting.photobucket.com/albums/gg18/barry2952/1%20Mark%20II%20docs/.highres/IMG_0115.jpg

[JohnC]

I like that set up. So you're 19-21" at that spot? I was hooking my vacuum tester to the windshield wiper tube coming of the vacuum pump. No good?

[Barry Wolk]

That's after the pump. You should be testing manifold vacuum. You should do the discovery, as I suggested, before doing anything else. Unless you determine where your vacuum drop is coming from you're literally spinning your wheels.

[JohnC]

That's my plan...test at the manifold and this this weekend I will hook up the complete vacuum loop, (all new hoses and T's), re-test and take it from there. Thanks again