Gas Cap Issues

[DT1]

I'm having trouble with gas caps on the 71.
It has a vapor recovery canister so I really don't need a vented cap.
The problem is that I can't seem to find an OEM type cap that doesn't leak.
I've ordered and received at least three non vented caps from different internet suppliers but all of them leak when the tank is filled to more than 3/4. I've looked at the filler neck and it seems to be fine. I've even tried a vented cap and it leaked like crazy. Another thing I've noticed about every one of the caps I've ordered from LMC, Ecklers, Etc is that they have all arrived with some sort of dent in them (Only cosmetic, on the top). I can't help but think these companies are selling blemished caps because they're boxed new and shipped in yet another box but still, all have been dented on arrival. Anyone here have or had this same issue?

[Sicklajoie]

I've had dented issues too.
Have you tried one from NAPA??
http://www.napaonline.com/Catalog/Ca...060_0348597155

[boynton]

I had the same issue on my 68 (sold) it was because the filler neck was slightly distorted on thr inner lip. If it is not completely flat it will leak. I did get a cap from my local oreily's which helped but a tepair on the neck or a new tank would have fixed it completely. I know you said you looked at the filler neck, but a good way to check it is put a flat piece of metal or a strait edge on it and see if there is any dent or lip on it. I think lmc also sells an extra thick gas cap grommet.

[boynton]

I actually just looked and there is a specific neck grommet for 71/72 it is 1 1/2" part number 30-1250 maybe it is that simple?

Edit Disregard that is for the tank to cab mount.

[Southcity]

It could be a couple of things, usually a distorted or warped filler neck so no gas cap will seal correctly. One easy fix is to purchase 2-3 of the same gas cap and transfer the rubber washers to double up, this did the trick for me on several of my rides.

[DT1]

Thanks for the replies. I checked the filler neck with a straight edge and light. looks OK to me so I'm going to order the NAPA cap and cut a gasket from some 1/8" silicone rubber if it fails to seal properly. I'm just getting tired of cleaning the residue from the side of the truck.

[69GMCLonghorn]

I've owned 3 of these era trucks. Every ONE of them dumped gas when I turn to the right. I swear I actually got 18 MPG out of my trucks when I only went straight or turned left!

I just bought a cap for my '70 through LMC and it is pretty good so far, but not perfect. I bought a non vented cap and realized recently that my vapor canister is there but disconnected. I'm going to run the lines to it in the near future to make sure it's doing what it should. The non-vented caps definitely leak less.