‘72 304 Ported Vacuum Switch Mechanics

I understand the purpose of this “switch” but I’d like to know how it works internally. Can’t get my mind around it after reviewing the TSM. Does that center piece actuate back and forth inside the switch column directing vacuum between the three hose connections for instance? If so, should I be able to slide it back and forth? Should those divots in the end that goes in the housing be open in some way and they are just closed off with crud? Trying to determine if it is actually “bad” or not. Maybe that will have to wait until I get my rebuild done?

 

Under the hood mysteries: Distributor Vaccum Control Valve.

Still puzzled? You can test it by dunking the end in boiling water, I presume. Don't put the whole thing underwater.

 

Thanks, perfect! Would you put Teflon on threadlock on the threads to install or just leave them bare? Looked bare coming out, but of course it’s getting closer to 50 years young.

 

Teflon. Makes it easier to take back out.

 

Yep, I'd use Teflon tape on these. No tape or dope on electrical sensors (oil pressure, water temperature) since it may interrupt the ground through the engine block.

Note the article is discussing what Jeep would call a HDC CTO (heavy duty cooling temperature controlled override). Your 304 uses a "spark CTO" which connects manifold vacuum when the engine is cold (more advance, higher idle, better drivability), and ported vacuum when it's at normal operating temperatures. You understand manifold vs. ported vacuum? The spark CTO's purpose is to retard the spark at idle so that you have lower NOx emissions at idle. Same device, different purpose, with the inputs switched. The HDC CTO did not appear on Jeeps until the '80s.

 

With Tim's help, I just got two new CTO devices for my (freshly rebuilt) 232. I have a 3-prong for the distributor and a 2-prong for the EGR.

As he said, the 3-prong switches between manifold and ported vacuum based on temperature, whereas the 2-prong model only switches between something and nothing.

They are pure thermostatic devices, so you test by putting the copper tip into hot water. Some are 190 degrees, others may be higher or lower.