Hello all. I searched the interweb and didn’t find my particular issue. Here we go. Headlights off, engine idles perfectly and smoothly while in drive. From a stop, there is a fairly big hesitation about 70% of the time. 30% of time no issue. Now, headlights on lhs goes up, rhs does not go up. Engine surges at idle between 700-1100 rpm. Back and forth every few seconds. But…..and a big but….there is NO hesitation at take off. So obviously a vacuum leak. Did smoke test, with headlights off and down….i don’t see a leak. Putting smoke end in various headlight vacuum hoses. Put Headlights on and up, the driver side relay leaks like crazy and right hand actuator leaks a touch out end of boot. Rhs does not go up without a little assistance. I know it’s a vacuum leak, but don’t want to start throwing parts at it. Any help would be awesome !

 

https://www.corvette-101.com/vacuum.htm

Above is a step-by-step.
Check and repair all the vacuum components and hoses.

 

You might just order a set of new vacuum hoses for the year Corvette you have. The best source I know of is DocRebuild and he sells the best hose kits with all the correct sizes and color stripes. The shop I use for any Corvette work used them when they helped me out. They put the hoses on and they have worked for over 30 years on my 1968 convertible.

Finding the leaks can be hard on some years. Some of the earlier C3's have had cracks develop in the Vacuum storage canister. It looks like your Vacuum reservoir should be up front near the 2 relays and both actuators. That is the best place to start since you have headlights that are not operating in unison. It is likely your leak would be in this area. When I have to chase a serious vacuum leak I use a 2 stage Vacuum pump that can pull a vacuum all day long and strong enough that I might hear it.

With a good accurate layout and a new set of hoses you will find the leak. And the car will have all new vacuum lines and it will work for another 43 years for you. If you try and keep the older hoses it might end up being a constant chase for leaks. The hoses are not cheap but they are very important for a good running engine

I had a check valve that slowly failed and that was a weird thing to have to troubleshoot. I would replace the vacuum filter and the vacuum check valve as part of general maintenance on the Corvette. Many times the leaky hoses could be made to seal by cutting off the first inch and then applying a little grease to the fitting to help them seal after being together.

I have never touched any of the vacuum actuators on my car because they work and have worked for 34+ years that I have had my C3. After the hoses were replaced the car's vacuum system has worked fine ever since. Until that darn check valve slowly leaked the vacuum down in hours where before the vacuum decay lasted weeks.

 

Replace these rubber parts in both of the actuators.
Replace the leaking relay.
As said above, cut an inch off of the hoses and check that there are no leaks at each connection.

 

Vacuum leaks are hard to track down sometimes. What you could also try, disconnect the main headlight hose from the intake, near the back of the intake, then plug the open port on the intake temporarily with a rubber plug. Test if you have the same symptoms. If you do, start disconnecting all vacuum ports on the carb as well as the intake and plug up the ports. You will eventually find the source of the vacuum leak. Could even be the brake booster or hose. If all ports are plugged and you still have symptoms, then you may have leaks around the carb or intake themselves. This process will help you narrow down the cause and you may be surprised of all the leaks you may uncover.

Good luck

 

Just do an electric headlight conversion. You can't even fix the stock system for what one of those eBay kits cost. I have one of those inexpensive kits and it works great!

 

Exactly.

Isolate the possible sources of vacuum leaks by blocking all ports that lead to headlight and HVAC components, then swap to electric headlights.

A plug kit like this will get you started.

 

I replaced the hoses and relays and rebuilt the canisters in my 82 and it only took a couple of hours and the headlights work great.

JT

 

Relays are rebuilt better than new by Dave J. Actuators generally just need a inexpensive seal and boot kit.
The vacuum system is extremely simple and very reliable. If it lasted nearly 50 years before it gave you any trouble how is it that makes it a poor system?
Hard to locate a vacuum leak? It really shouldn't be.
Convert to electric for less? I don't think so.

 

I know so.
And the electrons don't leak out after 5 minutes either.

 

Now I'm curious about the cost so I looked up Richard454 ebay listing and the kit is $549 to $619. From what I've read about the conversion if you do it Richard has the best kit.

Actuator kit $19 each, relays (pair) $89, a complete vacuum hose kit for the whole car $100 all from Zip for a total of $208

Looking at Richard's kit he uses the low beam to trigger the relay to raise and lower the headlights so that part is just plug and play. However you still need a 12v power from somewhere to run the two motors.

JT

 

many hours after I shut off my car. I can pull the headlight switch and my lights pop up. Granted there isn't enough vacuum to put them back down again without restarting the car. But that has never been a problem.
At one time I has a bad check valve and it would lose vacuum. And I needed to replace the check valve.
Of course the check valve was about 45 years old.
I wonder how long the cheapest electric headlight door motors will last???

 

I had to replace the relays and check valve shortly after I got my car. Those 3 items cost $120. Those eBay are down to $95. As far as longevity goes, all hear are you guys constantly complaining about vacuum system headlight parts that they fail within a few months. Well I've had my eBay system for a couple years now without issue. Just because those eBay kits are inexpensive don't mean the motors aren't going to last as long as the pricier kits. I know there's a lot of Richard 454 fan boys here and I'm not going to get dragged into a debate about Richard's kit vs the eBay kits. I just don't care for the long shaft/offset bellcrank design of his kits just so you don't have to do any cutting. And that's all I'm going to say.

 

Wow Detroit Speed C3 Electric Headlight Door Kit 122010DS is only $1,049.95

C3 Corvette Electric Headlight Motor Conversion Kit from Fleabay is $250 what a difference in price.

I didn't find the $95 kit on Fleabay.

I did find the $95 through $309 kits on Fleabay which all look the same to me.

JT

 

I bought my kit a few years ago and I paid $195 for it. The same seller is now selling the same kit for $95 now.

 

Thanks all for the input. I replaced the rhs actuator and the relay. It is much better, no more hesitation, and both headlights work as they should. It seems to idle a touch high around 900 in park and in drive. Thinking I got rid of the big leak, now have a little one. I like the idea of blocking the ports 1 at a time to isolate. I also like the idea of replacing all of the lines as they are 43 year old rubber. Any way, finally got to enjoy the CFI and it is fun to drive. Just fine tuning now, but I appreciate all the input. I’ve come this far, might as well go a touch farther. I did read another post about the throttle cable stop screw being messed with. PO must have done that as the weld was cut off. I turned it about 1 turn and it dropped 100 rpm at idle…. Keep on putzing !!!!!