M37 Fuel Filler Neck

[Dalton]

I have removed the bed from my M37 and in the process I removed the fuel filler neck from the bed and the gas tank.

There is some corrosion inside the neck. Inside I see about 10-15% rust and the rest looks like whitish paint, so overall it's not too bad. The part that slides out is stuck in and I can't dislodge it. The chain for the cap has come unattached from the neck and I don't see an attachment point.

How can I free up the part that slides out?
How should I restore the inside of the neck?

Also, raised letters on the outside of the cap read:
"Valve inside
Open-normal
Closed
Fording-vapor lock"

Is the valve the round piece on the inside of the cap? It has what appears to be a rectangular spring. Is this round piece supposed to turn? Mine doesn't.


As always, thanks for putting up with a newbie.

 

[DAP]

Yes on your gas cap, the spring is inside in the center and you typically turn it 1/4 turn to move from open to closed. It should always be on open except when fording so that the gas tank can breath.

Now the fuel filller neck - these were typcially not painted inside but rather galvanized of some sort so the whitish powder is likely corrosion. It wold be interesting to see if the inner slide out part is really stuck due to corrosion. Soaking it with PB blaster should free it with patience and time. However everytime mine got stuck it was because the clips and chain would slide into a crevice and jam the sliding portion. Extensive "fiddling" would eventually get the chain out and free. Then the inner portion would slide but was always stiff. I got so annoyed that I removed the chain and clip. just don't forget to put your gas cap back on securely -

When I switched to diesel the screen in the inner portion caused the diesel to back up and slowed fueling so I finally just took it out. Now I couldn't find where I put my inner slider part even if my life depended on it - sigh

 

[rosco]

After soaking the stuck part in your favorite snake oil (or diesel), turn it upside down and patiently go around the part where the lobes are and tappy, tappy, tappy, with a small hammer.

The neck and tank were galvanized (zinc) or tin coated. Probably galvanized. If the accumulation of white stuff (corrison) is bad enough, that you think it might accumulate to the point that it will be a bother, take a 1/4" piece of brass brazing rod, the appropriate length, and split the end so you can slide in a strip of plumbers scratch cloth. Put it in a drill and spin it in the filler neck. Or use some version of the above, but I wouldn't get too carried away, so that you remove what is left of the coating. Once its clean, and you start using her again, you shouldn't have any more corrison problems.

 

[Dalton]

Thanks for the help!
Forigve me if this is (another) stupid question, but how can I tell if the vent is stuck open or closed?

 

[DAP]

I think the position is marked on the inside of the cap. If all else fails pour PB Blaster inside the cap and see if it leaks. if it does then the vent is open. It might also free up the valve.

 

[GUNNY 155]

Was reading the open / closed vent comments on the gas cap. My M37 is in the process of a frame off restoration, so a long way to go. Just had my gas tank given the Tank Re Nu process. My gas cap has Pressure Cap stamped on it and I see nothing as far as a vent which can be opens or closed. Do I have the wrong cap? This also gives me concern about tank damage if it is the wrong one and is not vented.

 

[DAP]

The answer depends. If you still have all the fording equipment (lines) hooked up then it shouldn't damage anything. However if the vent lines are capped off or plugged it could cause you fuel starvation problems. What I did was get a cap that can be vented or changed to unvented. Then it doesn't matter. I see the caps on Ebay all the time and I know Vintage Power Wagons has them. I think Mid West Military also has them. A quick internet search will yield you multiple sources and prices.

 

[Mike_L]

I believe the "Pressure Cap" is the correct original cap on these trucks. Later replacements had the open-close option. The TMs show a cap with the 5 ribs on top that is the same as our "Pressure Cap" type.

As DAP pointed out, the original configuration would have the tank vented to the carb.