Another Fuel tank thread - 71 Demon

[Demonx2]

I've run into an interesting issue on my 71 Demon 340. This car was purchased new in the Cleveland Ohio area - I've owned it since 1984 and is basically an all stock and original car. So it is not a California emissions car. I bought a new tank for it before I crawled under there and found the old tank has the 4 vent lines coming out of the side. Well of course I had ordered the wrong one as the new tank has the single vent line in the front by the sending unit. Not to worry, I'll just get the correct 4-vent tank and pop it in and life will be good. NOT!!! (Note that I got both tanks from AMD.)

I learned that the 4-vent tank and the 1-vent tank are called an 11D and 11E respectively. It seems that sometime in the middle of the 71 Model year, there was a change made to the location of the filler pipe hole. The later tanks moved the fill hole rearward by 1/4"-1/2". At the time the fill hole was moved rearward, the vent system was supposedly changed from a 4-vent to the single vent. Hence the sequence change from calling one an 11D (4-vent, forward fill) and 11E (1-vent, rearward fill). So the 11E should have the more rearward fill pipe. I measured the 2 tanks from AMD and indeed the 11E filler pipe hole is more rearward by 1/4"-1/2" (hard to measure perfectly). This explains why you can order a 70-71 tank or a 71-76 tank...they apparently verlapped sometime in the 71 model year.

My car is a late-built 71 (ordered in March, delivered in May 1971). And of course nothing is easy....my car has the 4-vent tank that uses the standpipe in the trunk for the 4 vent lines to connect to but uses the later rearward location of the fill pipe hole! So I apparently have an 11D vent setup with an 11E fill pipe hole location. Well when you try to put the fill pipe in with the 11D 4-vent tank, you can get it in and attach it to the quarter panel BUT when you go to install the trunk floor seal....nope, it's too far forward in the trunk. And there's no way to stretch that thick rubber to attach it to the trunk opening. And if you did, I'm certain the tank filler tube rubber gasket would be compromised and that $5/gallon fuel would be splashing out! Also, I don't want that stress on the pipe to damage the quarter panel tugging on those 3 little screws attaching the filler pipe!

Anybody else ever run into this on a Duster or Demon? I'm thinking to use the later 1-vent line tank so the filler pipe/trunk floor gasket line up and just run that single vent line to the standpipe. I would just need to know which of the 4 little tubes going into the standpipe was the lowest so that any fuel fuel going into it could then go back out of the standpipe. Anybody know which one of the 4 tubes it might be?

Here's a generic sketch for the 4-vent system from I think a 73 service manual - I couldn't find a manual for a 71. Those 4 lines actually come out just forward of the filler pipe.

Someone out there knows these fuel tank systems better than me and can maybe shed some light on this!!

 

[70dart340]

Watching....

 

[doug 371]

I think all the 71's had it

 

[townsend]

The picture you posted is from the 1970 Dodge chassis service manual , page 14-117.

 

[Oldmanmopar]

Show me a picture of the back side of the gas cap and the inside end of the fill tube.. I have 2 late build Demons and also had several Duster and Demons in the past. All my 71;s had the . Vent tube. If you bought the car in 84 that means it was 13 years old before you owned it. Many collision shops would use 70 Dusters and 72 demons to clip 71 Demons in the early 70's for insurance co. repairs at dealers. Even 73's were used. Done right you would never tell.

I am not saying you have one but its worth a look. Send some pictures of your gas cap that would be the first clue. If the tank had one single vent in the front it is a 72 and newer tank. That hose went to the charcoal canister. I ran that tank in a 71 and ran the vent tube to the three nipple 71 oil breather.

Does your car have the correct oil breather and what is it connected to. Pictures would help. Does it have a rally dash. how about the screw hole that held the passenger side exhaust hanger on. Many think they know what they have because they have it for many years.

What I would do? Not saying I have any experience at this is use an extra tank pad and add a folded piece between the tank and the front of the tire well. Make it three thick . Not saying I ever did this but it should work LOL

 

[Mtrhead]

I have same setup on my 71 demon ,and I also need a tank...hope mine is all 11D

 

[72bluNblu]

First, if the car has the 4 vent tank and smog riser it is an emissions car. They started earlier in California but the single vent is the non-smog set up and the 4 vent with the riser is the smog set up.

Second, and don’t take this the wrong way, but the hole in the floor pan, the quarter panel mounting location for the filler tube, and the filler tube rubber are all the same. The filler tubes are basically the same too, the cap style and whether the tube mounts inside or outside of the quarter changed (and not until ‘72) but beyond that they’re all interchangeable.

I converted my ‘71 Dart, which had the smog riser and 1 year only cap over to a ‘74 tank and filler tube. In fact many people have converted their emission equipped’71’s to other model year tanks and fillers because the caps for the emissions tank ‘71’s can be difficult to find and very expensive. The mounting hole pattern from the quarter to the filler tube flange is different but beyond that they swap right over, even changing the tube flange from inside to outside.

I’m not saying the filler hole isn’t a 1/4” different. I’m just saying none of the other parts are. Which means you can get them all to line up. If the rubber seal on the filler is bound up, loosen the tank straps some and the tank will shift about. It’s not an exact deal.

(edit- changed '73 to '72)

 

[Oldmanmopar]

up until 72 all fill tube flanges were on the inside of the quarter panel. The screws threaded into the filler tube.

All 72 and later the fill tube flange was on the outside of the quarter and the screws threaded into the quarter panel.

67-70 all had a fill tube vent line and a non-vented cap

71 was the only year the the flange was on the inside of the quarter with a special low locking vented cap

All sport style cars Duster, Demons, and Dart sports, and Barracudas came with 3 attachment screws

All Darts, Valiants, and Scamps came with 4 mounting screws.

They should not be exchange between the 4 and 3 screws because the flange on the quarters are different and will deform the quarter around the fill cap. The reason they are angled different is the quarter on the Dart , Valiant , and scamp are flatter . All the others are wider and bulged so the angle is different. They are also different lengths including Barracuda. But a 70 Duster will fit a barracuda.

So only the 70 fill pipe will correctly fit a 71 but you will have to add the vent pipe because the 70 cap is not vented. A 72 cap will fit a 70 but it will fit very tight.

 

[Mtrhead]

Steve you are the man!!

 

[72bluNblu]

up until 72 all fill tube flanges were on the inside of the quarter panel. The screws threaded into the filler tube.

All 72 and later the fill tube flange was on the outside of the quarter and the screws threaded into the quarter panel.

67-70 all had a fill tube vent line and a non-vented cap

71 was the only year the the flange was on the inside of the quarter with a special low locking vented cap

All sport style cars Duster, Demons, and Dart sports, and Barracudas came with 3 attachment screws

All Darts, Valiants, and Scamps came with 4 mounting screws.

They should not be exchange between the 4 and 3 screws because the flange on the quarters are different and will deform the quarter around the fill cap. The reason they are angled different is the quarter on the Dart , Valiant , and scamp are flatter . All the others are wider and bulged so the angle is different. They are also different lengths including Barracuda. But a 70 Duster will fit a barracuda.

So only the 70 fill pipe will correctly fit a 71 but you will have to add the vent pipe because the 70 cap is not vented. A 72 cap will fit a 70 but it will fit very tight.

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Neat and all but none of that really helps the OP or explains any issue he may have.

Maybe the conversion information I mentioned was unnecessary, but my point wasn't about the conversion per se. It was about the fact that the problem that the OP is having with the trunk floor seal shouldn't be a thing. The trunk floor seal itself was the same from at least '70-74, which covers several emissions changes with regard to the tank. The hole in the trunk floor pan didn't move, the same pan is used '67-'76. The filler tube itself didn't really change either, certainly not from '70 to '71. The cap changed, but the tube was still mounted inside the trunk, the angle didn't change, and the hole in the quarter wasn't moved from '70 to '71 (same exact quarter panel was used). Or for '72 for that matter, or even '74 even though those quarters had other changes. While the filler tube was moved from inside to outside of the quarter panel and the mounting of the cap was changed, nothing else regarding the filler tube changed from '71 to '74 for the same model car. Otherwise I couldn't have used a '74 Dart filler tube on my '71 Dart without running into the same issue. And lots of people change those 1 year only filler tubes out for other model years because of the scarcity of the caps.

So my point was that even if the filler hole in the tank moved with that emissions change in '71, nothing else did. Which means the factory and everyone else was able to use the same trunk floor seal despite that change.

 

[Demonx2]

Neat and all but none of that really helps the OP or explains any issue he may have.

Maybe the conversion information I mentioned was unnecessary, but my point wasn't about the conversion per se. It was about the fact that the problem that the OP is having with the trunk floor seal shouldn't be a thing. The trunk floor seal itself was the same from at least '70-74, which covers several emissions changes with regard to the tank. The hole in the trunk floor pan didn't move, the same pan is used '67-'76. The filler tube itself didn't really change either, certainly not from '70 to '71. The cap changed, but the tube was still mounted inside the trunk, the angle didn't change, and the hole in the quarter wasn't moved from '70 to '71 (same exact quarter panel was used). Or for '72 for that matter, or even '74 even though those quarters had other changes. While the filler tube was moved from inside to outside of the quarter panel and the mounting of the cap was changed, nothing else regarding the filler tube changed from '71 to '74 for the same model car. Otherwise I couldn't have used a '74 Dart filler tube on my '71 Dart without running into the same issue. And lots of people change those 1 year only filler tubes out for other model years because of the scarcity of the caps.

So my point was that even if the filler hole in the tank moved with that emissions change in '71, nothing else did. Which means the factory and everyone else was able to use the same trunk floor seal despite that change.

Thx to all...some pics because we all know it didn't happen without pics!! Maybe a little background on the car too. I bought it from the original owner - even got all the handwritten order forms when his mother ordered it for him! The car literally has 37k miles on it - had 34k when I bought it in 84. The car held its value as I essentially paid him what his mom had bought it for new!
Ok, here's the gas cap. Looks like a 71 to me.

Here's the original filler neck opening. It has the flat piece of metal that starts down the tube near the tip and sticks out the bottom about an inch.

Here's the original tank (black) and the 11D new tank. Hard to see in the pic but the filler pipe opening is close to 1/2" farther rearward in the orig tank. The opening angle for them matches so no issue there.

Lastly, here's a shot of the original fill tube and a new one from Van's. Note the new one is about 1/2" shorter even though the neck by the cap end is identical. (You can't see the bend in them by the opening due to how they are laying.) The seal looks like it would still be on the new tube but mighty close to the end!! And sliding the tank left or right is tough as the exhaust pipes want to hit the tank if you do that.

I was talking to someone at Van's who was telling me about all of this when I called about the fill pipe length. He got me to measuring and I found what he told me about the 11D and 11E tanks to be true when I ran into the fill pipe location issue. He measured another fill pipe length for me and it was the same as what they had sent me. I called Megaparts who was all out of them but said they get theirs from Van's anyway!

Anyhow, I share all of this so others can also learn from your collective knowledge. Thx ahead of time!!

 

[Oldmanmopar]

The tube pictured is the length difference between the Barracuda and Duster. I just sold a 70 Duster tube to someone withe a barracuda. it was longer by the same difference as you have shown. Longer is ok shorter Not correct. Use your old one . Zinc plate it. Very easy to do at home. Use a web search. we zinc plate parts. You can polish them or let them gray/silver

The tank issue can be solved with a thicker tank pad int the front of the tire well. As stated above I used part of the old pad and folded it in half and put in front of the tire well. It moved the tank forward and it fit without being noticable.

Your cap is a 71

 

[Oldmanmopar]

Neat and all but none of that really helps the OP or explains any issue he may have.

Maybe the conversion information I mentioned was unnecessary, but my point wasn't about the conversion per se. It was about the fact that the problem that the OP is having with the trunk floor seal shouldn't be a thing. The trunk floor seal itself was the same from at least '70-74, which covers several emissions changes with regard to the tank. The hole in the trunk floor pan didn't move, the same pan is used '67-'76. The filler tube itself didn't really change either, certainly not from '70 to '71. The cap changed, but the tube was still mounted inside the trunk, the angle didn't change, and the hole in the quarter wasn't moved from '70 to '71 (same exact quarter panel was used). Or for '72 for that matter, or even '74 even though those quarters had other changes. While the filler tube was moved from inside to outside of the quarter panel and the mounting of the cap was changed, nothing else regarding the filler tube changed from '71 to '74 for the same model car. Otherwise I couldn't have used a '74 Dart filler tube on my '71 Dart without running into the same issue. And lots of people change those 1 year only filler tubes out for other model years because of the scarcity of the caps.

So my point was that even if the filler hole in the tank moved with that emissions change in '71, nothing else did. Which means the factory and everyone else was able to use the same trunk floor seal despite that change.

You might want to read all of post #5. Oh yeah ' You just want to contra-dick everyone

Other info may be useful to other members and the OP to decipher what they have.

Troll on. If you don't like what ever I have to say don't read it. Block me. then you won't see it.

 

[Demonx2]

I got the 11E tank installed and am using the new filler pipe for now. The old tube is being prepped "just in case" as well.

Vent standpipe was painted up and reinstalled. On the vent standpipe, it turns out the 2nd large tube from the end is the "drain" on these. The single tube mates to the end tube in the pic and the drain is the larger tube 2nd from the opposite end.

 

[Demonx2]

Thought I should update and somewhat close out this old thread. Has it really been almost 2 years????

The installation of the parts is as noted in the last posting. Once all of this was done, I was able to finish the rest of the car (engine/trans installed, etc, etc) in May/June 2022. Since that time, the car has been driven to many shows/cruises without any fuel system issues. So apparently that fuel filler neck sits deep enough in the tank to allow for a seal. And so far, no tank venting issues either. But as always with these old cars, I keep my fngers crossed and try to just enjoy them!!