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Easily Replace that Leaky or Rusted Gas Tank in Your C3 Corvette

Shark Tank: Fixing a leaky tank in a C3 Corvette

Aug 19, 2016
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C3 Corvettes are over 40 years old and the ravages of time tend to win out in the end. After all, we doubt any of the parts designed by GM were meant to go that many decades without attention. Even something as seemingly bulletproof as a gas tank can eventually fail. Sometimes it’s water in the gas that causes corrosion, or maybe it’s the seam where the two halves are joined. In any event, a leaky tank is just dropping cash on the pavement one drip at a time.

We had a 1969 small-block Stingray at the shop that was someone’s daily driver. It had developed a small leak that later became a bigger one, so it had to get fixed and back into service. After calling Tanks’ Inc., we found the perfect replacement for our leaky original. We’ve always used Tanks Inc., for our fuel-injected tanks and nearly forgot that they make very nice replacement tanks for carburetor equipped cars as well. So, with a lift and a few tools we set out of revamp at least a small section of this well-worn C3 Vette.

1969 Corvette Fuel Tank Replacement Gas Tank 2/19

01. The gas tank in a C3 is hidden above the spare tire carrier, so first up was getting it out of the way.

1969 Corvette Fuel Tank 3/19

02. This revealed the old tank and the bracing holding it in place.

1969 Corvette Gravity Feed Line 4/19

03. We could also spy where the sending unit and gravity feed line mounted to the bottom. This was a good time to make sure the tank was empty of fuel.

1969 Corvette Locking Ring Gas Tank 5/19

04. After using a screwdriver and hammer to drift the locking ring counterclockwise, we were able to remove the assembly.

1969 Corvette Fuel Tank Replacement Gas Cap 6/19

05. On the top side of the tank there were no fasteners, so we just removed the gas cap for added clearance.

1969 Corvette Fuel Tank Straps 7/19

06. The tank is held in place by two straps that are parallel to the tank and perpendicular to the Corvette. Once they were moved out of the way we could twist and turn the tank out of the Vette. This would have been easier with the exhaust removed, but we managed to get it out.

1969 Corvette Fuel Tank Replacement Gas Strap 8/19

07. Here you can see the tank strap, which goes over the tank and then hooks onto the cross bar, which supports the tank. It seems like an odd way to do it, but we’re sure they had their reasons. You can also spot some fiberglass repair that the Vette had done in the past.

1969 1968 Corvette Fuel Tank 9/19

08. Here’s our leaky tank out of the car. We couldn’t find a hole, but it looked like the tank was seeping out of the flange that joined the upper and lower halves together.

Rubber Filler Boot 10/19

09. One thing we forgot to get was a replacement rubber filler boot. Volunteer Vette Products carries just the boot (PN FU020) for $20, or for $30 you can get the entire overflow kit (PN FU020R). Our project had to be back on the road before the end of the day, so this went into the “we will do it later” category.

Gas Cap Flange 11/19

10. The gas cap flange was held secured to the old tank by 10 small hex-head screws that we pulled so we could transfer it to the new tank.

Gas Tank Hardware 12/19

11. The Tanks Inc., fuel tank include new hardware, gasket and O-ring for the replacement tank. After all, what’s the point of replacing the tank if it just leaks from a new spot?

18 Gallon Gas Tank 13/19
18 Gallon Gas Tank 14/19

12-13. The 18-gallon tank from Tanks Inc., (PN TM33C or GM33C) fits 1968-’69 Corvettes with everything from the 300hp 350 to the 390hp 427 with a single four-barrel carb. It had a vent bung and the tank was fully galvanized inside and out. Tanks Inc., also offers an EFI version.

Original Fuel Cap Flange 15/19

14. We then transferred the original fuel cap flange to the new tank using the new gasket and gasketed screws that came packaged with the tank.

1969 Corvette Gas Tank Install 16/19

15. When installing the tank, gravity isn’t on your side, so two people make it much easier. The hardest part was keeping the overflow boot in place while rotating the tank into position.

1969 Corvette Crossbar 17/19

16. With the tank held in place, we reinstalled the crossbar and hooked in the two straps.

1969 Corvette Sender Fuel Feed Assembly 18/19

17. We could then reinstall the sender/fuel feed assembly using the new O-ring and drift it tight using a hammer and flat-blade screwdriver. Once tight, we reattached the wires and fuel line.

1969 Corvette Fuel Tank Replacement Gas Tank 19/19

18. And just like that we were done and, after filling the tank with fuel, we were leak free and back on the road, which is exactly where a Corvette belongs.


Best of Show Coachworks
San Marcos, 92069
Volunteer Vette
Knoxville, TN 37914
Tanks Inc.



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