Hi everyone,
I just bought a beautiful 78 corvette about three weeks ago and this morning I had a puddle of gas under the car in my garage.
My working on cars in the past was limited to cleaning the windshield and replacing wind shield wipers, I am an IT guy and bought this toy to have fun with, not work on it. So as an IT guy I spent the last 90 min reading through old threads on this forum and acquired quite a bit of knowledge, but I think my situation is not covered somewhere else.
First, my leak is on the left, not on the right where the fuel lines come in and out. I took the spare tire off!!! (the most I ever worked on car in the last 20 years) and located the wet area just where the metal band is fixed to that metal bar. Now you need to see this car to believe it, I'll post some pictures later, there is no rust at all to see at the whole car. The tank shines like new. According to the previous owner this car was caught in rain only 4-5 times in the last 18 years. So I think I need a new tank and here comes the part where I need your expert help:
I made arrangements to drive to Detroit to impress a beautiful girl next Saturday, so I need to have this fixed rather quick, A friend who is a car mechanic will assist me (OK, the other way around). How do I get a new tank fast ( living outside Madison, Wi ) for a reasonable price, and how do I get the old tank out without breaking anything else. I am basically looking for step by step instructions, as my mechanic friend is not specialized on this car. I am willing to spend some money to buy a book or preferably download it right away, but as I am new the vette world I need you to point me to the right direction.

Thanks a lot in advance, I know I'll get a wealth of help and info here.

 

Exact same thing happened to me. Turned out to be the fuel separator.

 

 

You need to locate the specific source of the leak. You won't know how to fix it until you do. And, you shouldn't drop/replace the tank until you discover the source. There are many possible sources which will not require tank removal. I think you said that you removed the spare tire. If you haven't already done so, you need to remove the tire tub, also. This will give you much better access to find the problem. It only requires removal of the 2 [inboard] hanger studs and 4 bolts on the upper cover (2 on the latch bolt retainer). I highly doubt that you have a 'rust through' situation. It is most likely a damaged/cracked fuel separator unit {which is mounted to the left side of the tank} or a "rub-thru" area under one of the retaining straps.

Also, if there is a small hole that has developed in the tank, there are 'quick-n-dirty', temporary solutions...like a small sheet metal screw with a synthetic rubber washer that can be screwed into the leakage hole and snugged down to prevent any further leaking. That can survive quite a while until you get the time and parts to make a permanent fix. The most likely leakage source is the fuel separator unit/hoses.

 

The Assembly Information Manual (AIM) for our '78s shows the end of the fuel overflow tube is attached to the rear frame crossmember near the threaded fastener end of the driver's side metal band securing the fuel tank. Could be that you simply overfilled your gas tank and gasoline overflowed out the filler cap and exited through the overflow tube?

Also, our '78s do not have a tank mounted fuel/vapor separator as shown in the AIM page for a '74 Vette above. Instead, our cars have a fuel vapor canister located under the power brake booster can. It is connected to the gas tank via a solid tube running along the driver's side frame and connecting to a nipple on top of the gas tank just to the driver's side of the fuel tank fill assembly. A short hose also connects that nipple to a separate pipe on top of the fuel tank fill plate assembly.

 

drspencer, petes74ttop,7T1vette and 78IndyPace, thank you all for your replies.
First, as you might guess by my sometimes funny grammar mistakes, I am a German and getting into a new area here where I might be missing words or using them the wrong way, so please bear with me, even if some things sound strange.
I removed the tire tub and made a few pictures, try to add one here, but just in case I can't do that quickly I also created an album.
Last night my friend helped me siphon out all the fuel we could get out but it was still dripping all night long. I am sure there is a gallon or more left in the tank, but this indicates that the issue is really at the bottom of the tank. I also looked and, where I couldn't see, felt my way around all the sides of the tank, they are dry, so this is another indicator nothing is dripping down from some where else.

7T1vette, as the pictures should show, there is no rust, but it could be a rub through. Thanks for the hint on 'quick n'dirty', I will consider that to not miss my dinner in Detroit. But the last thing I want to do is to be too dirty, have fuel drip on my hot muffler and set the car on flames.

78IndyPace, is the AIM part of the standard doc that comes with the car? Not sure if I have that, but if not I am sure I can buy it somewhere.

 

Probably from water in the gas near or at the bottom of the tank, wipe it clean and dry so you can see where it's coming from. If there is just one hole rather than many, you can try the screw trick or even solder the hold shut. You tank may be in poor shape inside, but this will get you by for a while.

 

My bet would be you have some pin holes in the tank. The 78 has a plastic liner inside that will sometimes crack allowing gas between the liner and metal tank.
My 11K mile 79 had pinholes, in an otherwise mint looking tank. Looked around for another nice original and the first one I came across...had pinholes too. Seller never even noticed them.

Got a NEW one from an ebay seller. Buy it now, $225 plus $20 shipping. It was dropshipped out of Mid America Corvette in Illinois. Had it in 2 days.
Was cheaper this way than actually getting it from Mid America.
Funny, the shipping charge on the mid America invoice to the ebay guy was $7, compared to the $30 or so they would have charged ME.

I've had tanks out of 3 of my Corvettes over the last few years. With a lift and everything coming apart cleanly, maybe an hour to remove it and an hour to replace it. A lift definitely helps! Of course, siphon the gas out.

Ebay seller is...."thepartsladi"

 

Step by step instructions...

Remove the gas door and trim, 4 screws.
Remove gas cap and pull rubber seal up out of the opening. Either disconnect the drain hose or pay attention to the route it takes under the rear end.
Disconnect the 2 wires.
To the right of the opening you'll see a metal retainer over the fuel line and return line. Pull it over and slide it back past the rubber connector hoses. I like to just reach in and cut the hoses with a razer knife. Tight fit, tho.
Underneath the car now.
Of course, remove the spare tire carrier(as you've already done)
With your dual exhaust, you can probably remove the muffler hanger to frame clamps and get it to drop down far enough for clearance.(with original Y pipe and cat I just unbolt the pipe at the cat and drop the whole assembly out of the car)
Note how much stud is protruding past the nuts on the tank straps where it bolts to the rearmost crossmember. Remove the nuts.
With a helper, remove the bolts holding the front tank support.
Remove the support and set it aside. Note how the 'tarpaper' shields are located on both crossmembers.
"roll" the tank slightly forward as you lower it and reach up with your razer knife and cut the rubber connector hose on the drivers side. This is the vent line.
Drop the tank.
Hopefully you'll find your build sheet!

Reverse for installation. It helps to put a little silicone lube on the lines so you can get the hoses to slip on easily.
Get the tank back in place loosely. Don't tighten up everything until you get the gas line and overflow line connected. The vent needs to be connected as you raise the tank back up, just like how it had to be disconnected when you lowered it.
Tighten the tank support straps so the same amount of stud shows through as before.

 

KapsSA,
thank you so much for your reply.
Already ordered the tank, and now that I read your instructions I feel much more comfortable to do this.

If you ever come to the Madison area, we have a nice micro brewery here, the tab is on me. (If you drive and want to stay alcohol free, we can find that too.)

Thanks,
Joe

 

Thanks for the invite. Don't really get up that way much any more, can't stand the traffic north of Chicago!!

Was gonna offer to help ya with it on your way to Detroit. I'm not too far from I80 which you'll probably be taking. Not sure how bad you're leaking, tho!

Forgot to mention the straps. Make sure you get them around just the tank, don't want to clamp the lines under them. I just kinda hang them over the tank as I raise it back up into place, then while my helper is holding the tank I get the one end hooked back into the support and the stud end back through the hole for the nut. They can be a pain!