Fuel Venting - Leaking

[dfrazz303]

My '70 D100 has an in-cab fuel tank with two vents on the top. The PO had both vents connect with a "T" that ran down out of the cab to a fuel filter that had a constant drip of fuel coming out. The fuel sending unit was so loose you could move it around and it leaked fuel out the top. The fuel cap was not vented, so I temporarily drilled holes in it to allow some venting. So I'm looking for help to try to keep the in-cab tank and fix the venting and leaking.

I've read about the vapor canister on the passenger b-pillar with the 2 in - 1 out to the breather cap, which I do not have any of these parts. I've also read that most tanks up until late '70-71 did not have the vents on them. So can I just cap the two vents and buy a vented fuel cap?

For the sending unit, I have 2 that the PO gave me that do not register on my ohm meter and have the new thin lock rings. I would like to find a sending unit that works with an original style thick lock ring. Any suggestions on where to buy one?

Thanks for your help.

[Conrad]

I would assume this is covered in a parts manual somewhere. I only have the '64 parts breakout.

Tanks Inc:
If you are running a vent line it is important that the line is ran higher than the highest point on the tank including the fuel filler neck. Also, the vent line cannot have a dip in it where fuel or condensation can get trapped in the line. If fuel becomes trapped in the line your tank will then build pressure or vacuum until there is enough pressure to purge the vent which will cause gas and/or odor to come from the vent line. If enough pressure builds up damage could be caused to your tank.

[MadMC63]

Do you have any of the old parts? The metal vent line that runs from the drivers' side vent to the passenger side, bolts to the cab just above the tank. The metal vent line that passes through the cab floor. The vapor canister that mounts inside the cab. The vent line that attaches to the frame and travels from the rear of the cab to the breather cap.

[dfrazz303]

No old parts, and the passenger b-pillar does not have holes or screws for the canister. I also do not believe the tank is original to the truck since it has markings on it that seem to be from a scrap or junkyard that someone resold. I found an original sending unit with original lock ring too that I will install. I'm going to try to just cap the two vents and run just a vented cap to see if that works.

I did find a vapor canister on ebay and will try that if the first method does not work.

[MadMC63]

I have a 1971 D100. Tank leaked so I took it to a shop for repair and they destroyed it. Apparently, I live in the part of Ga where inbreeding isn't frowned upon. Point being I have all the EEC parts and no tank to attach them too. Currently in the process of installing a 68 Mustang 22 gallon fuel tank where the spare used to go. When I say I have all the parts I mean that literally.

[MadMC63]

If your truck doesn't have holes in the B pillar then it probably didn't come with EEC and not all did. There have been multiple threads in this forum regarding fuel leaks and several of them were solved by replacing the faulty vented gas cap.

[dfrazz303]

Update - I removed the tank and found it to be in good shape, no leaks. I bought an original sending unit and lock ring since it is thicker than the new Chinese crappy remakes, a new Gates vented fuel cap, and plugged both vents. Drove the truck around, filled it up about 2/3 and the truck runs great and no fuel vapors in the cab! This will work for now so I can drive it all summer and I may look at relocating the tank next winter.

Thanks for all of your help!

[PwrWgnDrvr]

Ive driven swepts daily for over 40 yrs. Ive rolled speedo's over more than 4x, one truck twice! ALL have in cab tanks. The only issues with gas leaks or fumes have been worn out vented caps that leak or once a tank got a hairline stress crack that seeped. Of the millions of sweptline trucks built, how many do u think have had the tanks moved out of the cab? That's a fool's errand if there ever was one!

[johnah]

I have a 1971 D100. Tank leaked so I took it to a shop for repair and they destroyed it. Apparently, I live in the part of Ga where inbreeding isn't frowned upon. Point being I have all the EEC parts and no tank to attach them too. Currently in the process of installing a 68 Mustang 22 gallon fuel tank where the spare used to go. When I say I have all the parts I mean that literally.

MadMc63 I've been looking at the 22 gal tank install myself, let us know how it goes.
Thanks in advance John

[MadMC63]

I wasn't willing to sacrifice the frame cross brace so I have started over with the 16-gallon tank. The 16-gallon tank doesn't require cutting anywhere and is almost a bolt in. You still have to make a frame to hold the tank but if you just wanted to slam it in you could probably mount it with Unistrut from your local hardware store.

[Conrad]

Ive driven swepts daily for over 40 yrs. Ive rolled speedo's over more than 4x, one truck twice! ALL have in cab tanks. The only issues with gas leaks or fumes have been worn out vented caps that leak or once a tank got a hairline stress crack that seeped. Of the millions of sweptline trucks built, how many do u think have had the tanks moved out of the cab? That's a fool's errand if there ever was one!

I think you could argue that most of what has been attempted by the prior owner and is being attempted on my truck by me as being a fools errand!

[PwrWgnDrvr]

Ive driven swepts daily for over 40 yrs. Ive rolled speedo's over more than 4x, one truck twice! ALL have in cab tanks. The only issues with gas leaks or fumes have been worn out vented caps that leak or once a tank got a hairline stress crack that seeped. Of the millions of sweptline trucks built, how many do u think have had the tanks moved out of the cab? That's a fool's errand if there ever was one!

I think you could argue that most of what has been attempted by the prior owner and is being attempted on my truck by me as being a fools errand!

Good one!

[moparbay]

I have moved the in cab fuel tank to a mustang 22 gal (Tanks Inc.) when i did my Fuel injuction setup. I didn't have to sacrifice any crossmembers. I did how ever have to notch the corners, and i welded angle iron to repalce the radius corner i cut out with a square corner. Some pics can be found
viewtopic.php?f=34&t=40012 little more than halfway down on the first page.