Vacuum switch. I cleaned up the Vacuun switch this evening not really knowing what it does or how it works. I notice that there is a number on the bottom, 230. I then realized that is probably a temp since I know that engines run up in or near the 200 deg temp range.
So, I realize this is a switch that activates at 230, but what does it do?
Is there a way to check it? or will it be obvious while car is running?
thanks bill v
69 Firebird Convertible (wifes car since 1979) Goldenrod Yellow, 350, plain Jane Car was stored in garage since 1990
I need help, if anyone see's I'm going down the wrong road--Straighten me out!
That should be the switch that operates during warm up and sends vacuum to the air cleaner flap that pulls up the warm air from the exhaust manifold. It may also cut out the vacuum advance.
I doubt that it switches at 230 because you would be very close to overheat at that point.but I believe it does open or close at some temp to allow vacuum from different sources, or not at all, to change your timing as needed for one reason or another. Pretty clear right? I know one thing, don't break it. Those things go for much gold. Do you still have the rubber piece that slips over the ports?
In '68 it is a combination of an emissions control device that compensated for leaner carb settings and also was intended as an overheating safety device. It would both retard and advance the timing using opposing ports on the distributor vacuum pot.. The retard function was eliminated with a Pontiac Technical Service Bulletin in '68 which eliminated the use of two of the ports on the TVS. Second, if the engine overheated above 230 degrees, it would adjust the timing to help cool down the engine. I believe the Diagnostic Manual has a better description of the TVS than what I remember and it may describe and how to test it. I can copy the Diagnostic Manual pages if you need them. And I believe I also have that bulletin that modified the vacuum lines.
Well I stand corrected about the 230 degree thing. I guess it makes sense that something would get adjusted to attempt to cool the engine at that point before temps got any higher and an overheat condition was eminent. Didn't the 68 distributors com fitted with dual pot vacuum canisters?
The service bulletin that suggests to disconnect carb and distributor advance hoses is somewhat deceiving to me and it referes to 2 speed transmissions (clunk) and then it seems it ONLY applies to 68 Firebirds 350 2bbl, 68 Pontiac 400 and 68 GTOs 2bbl unless they mean "All" Pontiac 400s, although the do specify Firebird 350, but not Firebird 400, although the emission labels confirm the tune up specs listed in the bulletin on 400 birds. Thoughts?