1940 Fuel tank leak

D

dajo

Junior Member
New here just got a 40 standard 4door that is original and unrestored. Drove it home over 100 miles without issue. Almost everything works on the car. Speedometer was 15MPH fast.
When I filled the gas tank completely up it leaks fuel from the top area that can not be seen. Looks like the tank has to come out since there is no access thru the truck floor. Is the fuel sender the most likely source of the leak?
 
You can access the sender through a small metal cover in the trunk. I suspect it may be the sender gasket. All 40's have the small access door in the trunk for the sender. If you do not have the door then the floor was most likely replaced.
 
My "54 Merc ragtop had a leak when full. Come to find out somebody stuffed a towel in between the tank and the trunk flooring I assume to reduce a rattle. We removed the tank on my uncle's garage sidewalk. Uncle Raeman had me thoroughly wash the tank with hose water. Then he tossed a match in the tank. The tank jumped 4" after which he had me sweat-solder flattened Cambell soup cans over the many holes. She lasted thru collage and USAF flying school until new wife vetoed the car. That wife gone, but I wish I had the Merc: de- trimmed, lowered, OD added, duals and Smitty muffs repainted 1956 Plymouth icebox white with red/black interior. Bought it from ACE Ford in Woodbury, NJ, with 150,000 on the car and 48K on a replacement motor. Who got her(trading in 1961)
 
If someone replaced the trunk floor and didn't put the access plate back in that was pretty poor. It may be there but covered with some sound deadener. It isn't very big, just large enough to remove the sender. Maybe pump or siphon some gas out of the tank and see if the problem goes away. Somebody with a 40 4 door can measure where to make a new access. If it were a coupe or station wagon I could make a template for you. Look closer for the original access, maybe scrape the floor looking for a single screw that holds the cover. Good luck.
 
Just a couple of weeks ago I had fixed this very same issue for a friend.
The Drake sending unit, at least some of them, had a flange around the perimeter that was drawn too deep. Thus, it would bottom out against the tank and not allow the gasket to be crushed.
Also, the screws that came with the Drake sender were too long. Many of these tanks have blind holes. The (too) long screws bottom out and won't pull the sending unit down enough to create a seal.
And, one final note... do not top off the tank.
 
Found the access plate, will investigate further. Thanks

Any ideas about the speedometer, don't really want a $400-600 repair as quoted by Bob's .
Tire size 6.00 X 16 pie crust Firestones, rear axle 3.78 verified by count ring gear teeth and stamped 9 34. Will be checking odometer today for accuracy.
 
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Change the "turtle" at the forward end of the torque tube where the speedo cable connects to one with a 19 instead of the one currently on there and I think your speedo will be correct.
 
deuce_roadster said:
Change the "turtle" at the forward end of the torque tube where the speedo cable connects to one with a 19 instead of the one currently on there and I think your speedo will be correct.
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I will check this out. I noticed pictures of oem units have the tooth number stamped on the cover. Can't imagine how this can be wrong one could be installed since this car is so stock and unmodified. If it is wrong can it account for a near 25% error?
 
Went to drive car today to check odometer accuracy and the speedometer is completely inoperative, no movement at all. Cable was not turning and froze up in the housing.
Started new thread on frozen cable questions.
 
40 gas tank has a filler neck connected to the tank with a rubber hose, Could be a leak where the hose connects to the neck or the tank. Good to check this out also.
 
Gas leak was at sender gasket. Someone put screws that were too long in a couple of holes. Screw heads rounded out. Replaced all screws (SS 1032 1/2" long) and sealed gasket with Permatex. Sender is a KS sender and still works. No more leaks now.
Still working on the speedometer and waiting for new drive cable.
 
To me your speedometer needs serviced.Over many years the lubricant dries out. I suggest you pull it and send it out for service. If you can't turn the stub at the threads for the speedo cable casing collar-don't connect connect it as gears might be seized inside.
 
I have pulled it out and got it working. Even calibrated using 38 coupe (thanks) method and found that it was only showing 8 tenths of a mile in 1 minute. There is a lever on the clock spring that changes spring preload. This was not difficult to do. Can not see how they want $400-600 at Bob's in Michigan. Still waiting for cable.
 
dajo said:
I have pulled it out and got it working. Even calibrated using 38 coupe (thanks) method and found that it was only showing 8 tenths of a mile in 1 minute. There is a lever on the clock spring that changes spring preload. This was not difficult to do. Can not see how they want $400-600 at Bob's in Michigan. Still waiting for cable.
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You may find out sooner than you think. Most of the folks offering services in the old car world are skilled technicians and offer excellent services at a fair price.
 
dajo said:
Gas leak was at sender gasket. Someone put screws that were too long in a couple of holes. Screw heads rounded out. Replaced all screws (SS 1032 1/2" long) and sealed gasket with Permatex. Sender is a KS sender and still works. No more leaks now.
Still working on the speedometer and waiting for new drive cable.
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I hope for your sake you used a sealer that is designed for contact with gasoline. Many, perhaps most are not. If you didn't, you'll end up with "mush".
You should not need sealer in that area. The screws you had used (1/2") length, are longer than originally utilized.
I am willing to bet they are bottoming out.
 
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