I think you need the service manual for your car. It shows the answer to most your questions which are plentiful. If you want to get to the bottom of everything it’s going to involve work and perhaps draining your tank, pulling the sender to look in the tank to see if the lines are reversed to at least know where you stand.
Follow the line in the trunk, it comes into and then goes out of the trunk into the frame rail outside the trunk/cabin of the car.
Your car requires a NON-vented cap.
I believe stock 70 b bodies had a return, 69 and down did not.
You will need to check the schematic in the service manual.
Checking all lines for obstruction is a good idea. Perhaps ethanol laden fuels has swollen one closed creating a pressure situation, who knows.
Again, get the service manual and start going through items one at a time.
If anyone can me in the service manual where this is solved that'd be fantastic. Because I HAVE A SERVICE MANUAL and there are multiple threads on this forum and the A body forum and the other MOPAR forums about this identical problem, none of which have been thoroughly solved, all of which have had the same possible solutions thrown at them (mostly
dadsbee suggesting the lines are reversed if the tank is aftermarket which sounds like a probable culprit but, again, NO ONE confirms this is the case or that it solved their leakage, and if it did they never came back to tell us) or going with a vented cap, which now cost like $150 for an OEM and everyone says the aftermarkets don't work so I am hesitant to throw money at that if it's not going to help (and it sounds dubious). Nor does the service manual cover ANY of the issues I have been having, like the problem with multiple O rings of varying thickness (NOT DIAMETER!!!!) being included with aftermarket oil pump rebuild packs without explaining which is OEM and which is for the aftermarket pump, nor the wiring for aftermarket ignitions and tach adapters with extra fuse boxes for my old model, nor aftermarket linkages for modern carbs, or anything else I am struggling with. I am not working with a factory original machine or doing basic maintenance with known OEM parts here. The manual is not a troubleshooting diagnostic tool or a magic spellbook for undoing 50 years of repairs and patches done by other owners, you pretty much have to know what's wrong for it to be of any use.
steve340 solved his by extending the tubes well into the trunk using larger diameter hoses, which worked, but still....
Hilljack68 resorted to a vented cap and a depressurizing ritual after each drive.
"Follow the line in the trunk, it comes into and then goes out of the trunk into the frame rail outside the trunk/cabin of the car."
Which I did. And I cannot find it. So I asked you guys where exactly to look because I've been under this car the majority of the last 5-6 afternoons with a flashlight crammed down the back of my throat getting my eyes full of debris and fuel with cuts all over my hands and forearms burning from this non E gas and I've run out of spots my eyes can see so I am wondering if it is tucked up into some metal fold that is out of sight and had hoped there would be a photo someone could post. In fact there is another post on this forum where a members says he also has the manual but requires a photo because the sketch is insufficient. But what I really needed to know was exactly where would I see the leak dripping so I can set some cardboard down and look for it.
"Checking all lines for obstruction is a good idea. Perhaps ethanol laden fuels has swollen one closed creating a pressure situation, who knows."
I used non ethanol fuel.
"pulling the sender to look in the tank to see if the lines are reversed to at least know where you stand."
Not. Going. To. Happen. Winter came last night. Full tank of gas. No room to make that mess much less clean it up without a yard and a hose. I will try everything possible before I resort to breaking that ancient seal and opening that tank including siphoning it all into my truck just to get the gas smell out of the new garage for the winter so my woman will shut up about it. If it comes to that it won't happen until May. So until then I will attempt every possible solution that does not require more fuel leaving the vehicle and getting on the floor.
OK man? I am here asking for help from people who have experienced similar problems, not someone wagging their finger telling me to read a book.
