i have the correct gas cap for my 70 chevelle and it is supposed to be vented yet it builds pressure up. how can i eliminate this pressure or is it normal?

I'd try another cap. If it's vented, it shouldn't be building pressure, period.

stroked70, I have the same problem,as so does a friend of mine.I posted this question some time back and was told it was the cap also. So far the original, two from Nappa and one GM replacment from chevelle supplier all say vented on them and the problem still exists.Still looking to solve problem,but car is sitting while other issues take priorty.Please post if find answer. Good Luck Jim.

Ok, i found my problem, but im not for sure it helps anyone out. My car originally came from California and was equipted with a charcoal filter. Of course i removed the filter and the line to the tank and pluged the holes. Recently doing some research in my Year One cataloge i found that the vented caps are for non EEC (evaporative emissions control). So in return I unpluged the hole to the tank and replaced emissions block type deal that the hoses from the tank lead to and left it vent there. I just put that on so it would vent properly, i didnt hook it back to the canister because i dont have the return line and the canister, also why would i put emissions back on. So far the tank isnt under pressure and have had no problems. Questions?.....write me!

It might be wise to put a canister back on the car if you are going to vent the tank to open air.
A canister not only will keep your garage from smelling like gas, keep the area around your car from smelling like gas, and maybe keep your house from blowing up (got a water heater in your garage? gas dryer?) but it will help the environment a bit at no loss in performance. It can also keep from sucking dirt into the tank when the tank cools, much as it keeps gas fumes down as the tank expands.
Why would you put emissions back on? Shoulda grown up in LA in the 70s with your chest aching in the afternoons from being outside playing in the smog. I don't want it to turn into a diatribe on emissions equipment, but every little bit helps, and if it costs nothing in performance, why not?
Just don't go putting a 4 cyinder in it so you get 30MPG. It just ain't right.
http://www.chevelles.com/forum/smile.gif

K

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64 2 Door 400SB/TH350 (actually IN the driveway!)
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"You laugh because I am different. I laugh because you are all the same."
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I think that "vented" for these caps means that they will let air into the tank but will hold pressure. That is why the car has a charcol canister. so that the fuel vapors will be absorbed and held in the canister.