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My 5 star has 2 positions, like a radiator cap. 1 click tight, then 2 clicks tight. 2nd click is for fording from what I read.

Tuko....I've heard of a cap like yours....but never seen one.

Chris,

Here's the deal as best I know. And this pertains only to the first series M37, not the B1. I don't even know which ORD pertains to the B1, let alone have a copy. ORD 9 for the first series M37 only lists one gas cap, the 5-star unvented cap. Fording instructions in TM9-840 make no mention of anything the operator has to do to the fuel system when fording. What that means is the fuel tank was vented up thru the carb elbow at all times. The cap was unvented at all times. As long as the vent from the tank to the carb inlet was clear there was no issue, and the unvented cap kept water from entering thru the fuel filler tube while fording.

Over the years people have disconnected the vent or it's become clogged, and used a variety of vented and unvented caps. Obviously the wrong combo of those two things leads to bad things. It's possible that the B1 had a vented or adjustable fuel cap....I just don't know. Other M-Series trucks did.........so it's certainly possible. But for the first series of M37s I believe the "correct" configuration is the unvented 5-star cap and a fuel tank vented to the carb inlet. The other caps you see are M38A1, M35, M715.....etc. At least that's my opinion based on what I'm seeing in the manuals.

regards,
bob

My cap does say "pressure cap" on it. This was not visible until I sandblasted all the layers of paint off.

I believe the vent on the tank that runs to the carb elbow has a check valve inside it that will allow pressure out of the tank, but won't let air into the tank.

Brett

Hi Brett,

Yes, you're right. The valve is located in the gas tank cover, the round part on top of the tank that has the vent and supply line coming out. There are two part numbers listed for this cover in the ORD, one for very early trucks and then the rest of the first series.

regards,
bob