My leaking vented gas cap fix.

[Keystone_Hate]

I have a 72 C10 with the in cab tank and it did not have the vent line when I bought the truck. Instead it had a vented cap. Well that one started leaking pretty badly so I went to Napa and got part#7031220. I saw someone else here had used that cap with no issues. I got it and put it on. No more leaky!! BUT I did have the big WOOOSH of air when I took it off. So I decided to dissect it. What I found is that the cap is in fact vented and there is a two way relief valve with one little spring to let air in, and one big spring to let air out. The spring to let air out is the issue. I tried blowing through the cap and with all my might I couldn't get the relief valve to let any air out. So here is what I did to fix that.


Bend the little ears up that hold the check valve in the cap.


This is the check valve that comes out


Pop the little center spring retainer out gently. Don't let it hit you in the eye.


Cut about one and half rounds off the big spring.


Assemble the same way it came apart.


I found that now the new cap seals tight and wont allow leaks, but with just a bit taken off that stubborn spring, it allows much easier escape of built up pressure, while still keeping the original function of the check valve. Been driving with it for a week and no issues. I tiny bit of air spits out when I remove the cap but that lets me know the check valve is still functioning. Have fun!!