'78 Chevy C20 truck gas filling problems

Hi there,

I was recently gifted a '78 Chevy C10 truck and need to resolve a couple problems. Being somewhat mechanically inclined, I’m happy to try and fix it myself. If its more complicated, I’d like to understand it before I pay someone else to do it.

The first issue is that I can’t put gas in the tank without it spilling out at my feet. I changed out the fuel hoses, both filler and exhaust, and still have the same problem. Actually it seems to be worse. There are two tanks–same problem on both sides. The exhaust hoses were cracked up before changing. Previously the gas leaked out from the underside of the body. Now it leaks down both sides of the body. I realize now the hoses weren’t the issue though its good to have them rejuvenated. I was considering changing out the filler necks but after some research that doesn’t seem to be the issue either (even though they aren’t sealing, hence the leaking fuel). I believe if there was a seal, I wouldn’t be able to put any fuel in at all. The pump would just shut off. It seems the air is not able to get out of the tank when the fuel goes in. I see that newer models having this problem when the fuel tank vent valve is clogged but from what I can tell that part is not available for the '78.

Is the previous iteration of emission control the vapor canister and would clogged one cause these problems?

And therefore would changing the canister filter take care of the problem?

Where is the canister located?

Is it easy to access?

The other issue is that the door has to be SLAMMED a couple times to close it properly so it won’t rattle. From what I can tell, changing out the hinges should remedy this. There doesn’t seem to be a spring so it should be pretty straight forward aside from supporting the door properly and wrestling the pins out.

Am I missing anything?

Input appreciated!



Find where the gas is spilling out of. I have to leap to the conclusion it is not out of the filler neck, have a friend fill it up while with your safety glasses on you see where it is leaking from, then fix it of course. I would think your suggestion would work for the door hinges but they can be a bear to replace and get aligned. Look for signs of wear and decide what parts you need. If the holes the hinge pin go into are larger that the pin replace the hinge. If the holes are fine but the hinge pin is worn you may only have to replace the pin. If the bolts that hold the hinge to the frame are loose you may get away for free by tightening them in the proper alignment. best wishes for an easy repair.

Hi Waterboy,

Thanks for your reply.

Before changing the hoses I described my problem-- leaking gas when filling – to an auto parts guy and he looked under the truck and then ordered me the filling hoses. The exhaust hoses were worse than the filling hoses, one of them being broken all the way through. Now that the hoses have been changed out, the problem seems worse in that the gas filler pump quitting as gas is coming out of the top of the filler neck and bleeding down sides of the body panel and dripping to the ground. Previously I would pump slowly to minimize the amount of fuel loss but at least I could pump. Now I can’t even pump as it quickly quits with big kick back splash around the pump collar. Again, it happens with both tanks so I’m wondering if it something further into the fuel system. From what I’m hearing, this was was not uncommon for Chevy trucks around this time as the filler neck is not much higher than the gas tank. I’ve yet to hear how it was addressed.

Thanks again for your input,

Try putting the nozzle in upside down. That’s what I usually have to do on my '76 C10 and even then usually I have to fill it up with the handle only partly held down. It’s a nice way to spend some time sitting there marveling at how sweet your truck is. Mine doesn’t have a charcoal canister or any of that nonsense (is yours a CA truck?), so this may or may not be applicable. But mine is a total pain to get gas into, and I know the evaporative emissions stuff isn’t the problem because it doesn’t have any!

Mine’ also got the door issue-- it may just be that the hinges need to be realigned as they sag with age and rust.

Trying to figure gas full myself but your door problem is not your hinges you need door sticker blots. Look at bolt inside cab the door latches too it is supposed to have plastic not just metal to metal for latching. Order bolts with new plastic online or can get cheap ones in help section of auto zone ect for 10 to 15 bucks. Or quick fick wrap electrical tape around bolt 15 or 20 passes and should close easy

door stricker

and I thought I was the only one that would replay to a 10-year old message. :grin: