When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
I have a vacuum leak in my headlight system in my ‘new’ 70 LT1.Using a vacuum pump, so I don’t need the engine running, I located leaks in both the large yellow and green hoses that go to the two vacuum switches in the front. I vacuum tested all the hoses, both actuators and they all hold vacuum. But when I apply vacuum to the main hoses I hear hissing coming from both valves. I bench tested one and it leaks vacuum. Could both valves be bad? Thanks Vacuum pump set up Left feed hose hook up Vacuum reading to vacuum switch Testing vacuum switch
I don’t know how to answer your question, but just zooming in on the last pic, could that be cracks in the switch tube?
Also, to find the possible culprit area (the hiss)… if you don’t have a Dr’s Stethoscope (who does?), where you could remove the flat portion on the end of it and use just the hose to search and pinpoint the leak, you can also just stick a piece of hose, holding one end into your ear as you move the other end along the system. I once had a mild exhaust leak (‘67 Firebird) and my roundy round racing brother in law helped me find it this way. He had an stethoscope with the end removed that helped me to find it. Since then, I’ve used just a hose (I own no stethoscope) to pinpoint other issues on cars by honing in on where the noise (whine, screetch, ping, knock, etc) was coming from. Hope that makes sense and hope it helps. Good luck with it.
BTW, I’m going electric on my ‘71 LT1 and pulled those. I know they are cheap enough, but if you want the one’s I pulled they are yours for the shipping costs alone.
Inside the valve is a rubber 'dogbone'. The vacuum slides it backward and forward.
You can get access to it by removing the little disc at the end of the valve.
I don't know if there's a source for them?
Your issue is an extremely common one. Your vacuum relays are leaking atmosphere into the vacuum system. Or also commonly known as leaking vacuum. In time the original rubber dog bone becomes brittle from ozone exposure and grime and crud that it loses it's ability to seal effectively. The simplest solution is to replace the relays. Unfortunately most of the replacements on the market are imported and not very good. Originals can be rebuilt. If you're interested PM me and I can help you out. If your relays are original, the script "AC SPARK DIV" will be molded into the relay body under the metal control chamber vacuum port. Also, original '70 relays have a unique metal top pictured below.
I have a vacuum leak in my headlight system in my ‘new’ 70 LT1.Using a vacuum pump, so I don’t need the engine running, I located leaks in both the large yellow and green hoses that go to the two vacuum switches in the front. I vacuum tested all the hoses, both actuators and they all hold vacuum. But when I apply vacuum to the main hoses I hear hissing coming from both valves. I bench tested one and it leaks vacuum. Could both valves be bad? Thanks Vacuum pump set up Left feed hose hook up Vacuum reading to vacuum switch Testing vacuum switch
Test the port on the actuator portion of the relays the must also hold a vacuum 7+in is all they need, your filter is missing on the relay showen in photo. You should see the spool moving up & down when vacuum is applied and removed.
Sounds to me the spool is either not moving or vacuum is leaking around the spool.
I'll just jump in here and comment.
Yes it's very possible that both your headlight relays are leaking vacuum.
Both mine did. And, it was just like all at once!
And Dave J. (Above) .
Rebuilt a couple for me. Truly great work. Highly recommended.
Headlight vacuum leak
