Gas cap and gas tank

by **gregvega** » 15 Dec 2007 22:52

I've got a couple problems. My year one pop top gas cap sits really high off the quarter panel and looks funky. It also doesn't fit in the recess very well. Now the gas tank, I bought a new after market tank with no vent line. What about the filler neck vent? My last question is should the tank straps have any kind of pad on them where they hold the bottom of the tank?

by **Jon** » 16 Dec 2007 3:32

The tank needs to vent somewhere. In your case it sounds like the cap. Do you have a vent inlet to the filler tube?

As for the pads on the tank, the factory didn't install anything as far I know. I did add some rubber pads on the radius corners thought. Also you will need a insulator between the the trunk floor and the tank.

by **christer** » 16 Dec 2007 7:48

gregvega wrote:I've got a couple problems. My year one pop top gas cap sits really high off the quarter panel and looks funky. It also doesn't fit in the recess very well.

Have you read this thread?

http://challenger.mpoli.fi/forum/viewto ... =1992#1992

by **dave-r** » 16 Dec 2007 13:27

Photos of the problem would help us a lot.

Yes there is a pad between the tank and the floor. I made my own from a material designed to protect your dining table from hot dishes?

The straps shouldn't need any padding.

If the filler neck has a vent you can use any type of filler cap - vented or not.

Why your cap does not fit i don't know. I can't see it.

by **gregvega** » 17 Dec 2007 2:59

I didnt read that thread before, its almost like that. It fit way off the fender too far, looks ugly. I have the trim ring but it doesnt fill in much. I'll try to get a pick. Should I just plug the filler neck vent fitting since the tank has nothing?

by **Jon** » 17 Dec 2007 14:49

I think the vent on the filler neck is suppose to connect to a 1/4" vent tube on the sender. Do you have a hose leading to that location? It vents the upper section of tank above the filler tube. Otherwise when the tank is full the pressure build-up would send raw gas up the pipe towards the cap.

by **dave-r** » 20 Dec 2007 18:13

My neck vent has a hard line connected with a rubber sleeve that simply runs down to the inside of the chassis leg.

by **Jon** » 20 Dec 2007 21:57

The upper section of the tank is vented along with an expansion capsule. Some after market tanks don't have this capsule though. If the tubes are not present how is the upper section vented. When filling the tank how would the trapped (now pressurized) vapor allow the tank to fill completely? With only venting at the filler neck, in warming conditions the trapped vapor would force liquid gasoline up the filler pipe toward the vent pipe.

The (aftermarket) sender I bought recently, has a 1/4" vent tube that would allow the vapors above the filler pipe level to be released. The filler neck would seem to be a good location to connect this line in conjunction with a vented gas cap.

Sorry for the rant. When dealing with gasoline there is a safety issue though. :s022:

by **gregvega** » 21 Dec 2007 17:01

I'm going to try and get a pic of gas cap today. I was thinking ahead about the gas tank installation. Is it better to mount tank then filler neck or filler neck then tank? I still dont know what to do about filler neck vent. I'd really like to use my new tank that doesnt have vent tube. My new tank sending unit doesnt have the vent tube on it either.

by **dave-r** » 21 Dec 2007 17:43

I usually find that it is easier to fit the tank first but leave it loose so you can tip it slightly. Then lube the filler neck with WD40 and push it in as far as you need to get the neck into the trunk. Then pull back out again to mate with the quarter panel.

Fit the sender unit last it case the filler neck catches it.

by **RedRaven** » 21 Dec 2007 18:11

dave-r wrote:I made my own from a material designed to protect your dining table from hot dishes.

This guys character was modelled on Dave because of his abilities!! :mrgreen:

by jr » 21 Dec 2007 19:00

And now I shall reveal biggest secret of known history... Dave-R is actually well known music artist Devastatin' Dave!

by **gregvega** » 23 Dec 2007 15:31

I looked at sending units on e-bay and some have the 2 lines 1 3/8 other 5/16 I guess. It looks like the 5/16 line feeds back into the 3/8 pick up line just after the mounting flange. I f I hook my vapor line to the 5/16 fitting do you think it would cause the 3/8 feed to pull air through it?

by **Jon** » 26 Dec 2007 21:02

If I may pose a question: what year Challenger do you have and did it have a 4 tube vented tank before?

Re: Gas cap and gas tank