Tech Tips with Steve Turchet

by Steve Turchet

No Fear

Why were U.S. Army vehicles painted shiny olive drab after WWII? Did the military think it didn’t have to hide the vehicles anymore?-—Robert Breathwaite

The simple answer is, “Yes.” The semi-gloss OD paint of most post WWII through late 1960s U.S. Army vehicles has been termed by some experts the “Fear Not” or “No Fear” paint scheme. Basically, it was supposed to say, “I am the U.S. Army! I won WWII, so you’d better not mess with me!”

This attitude changed during the Vietnam War, and flat OD and camouflage schemes were re-adopted.

STUMBLING MUTT

I have had my 1963 M151 for over two years. It was in storage for five years when I bought it, but it was in pretty good shape. I’m slowly doing a motor-pool restoration. One problem: I have not been able to fix is a stumble spot coming off idle. I kitted the carb twice with NOS kits. Suggestions?—Stan Burke

M151 and M151A1 MUTTS had a tendency to stumble off-idle as you describe. This was often caused by design flaw in the carburetor, and simply kitting the carb didn’t fix it. I assume you’ve checked all the other possible causes for a stumble—vacuum leaks, including in the windshield wiper system, cracks in various intake components, ignition timing, fuel delivery, and leaking gaskets? If one or more of these aren’t the cause, you may have one of the “stumble carburetors.” At least one company that advertises in this magazine offers MUTT carburetors and states they’ve eliminated the stumble problem.

FIRE WHEN READY

My ‘67 M715 started to backfire going downhill and when I let off on the gas and coast. Except for doing this it runs fine like it always did. Can you give me ideas what the problem is? —Mark D’Angelo

There are several probable causes for an engine to backfire, ranging from fuel starvation to incorrect timing, but since your five-quarter only does it in the situations you describe, I would first suspect an air leak in the exhaust system. This could be caused by leaking exhaust manifold gaskets, a loose manifold, a crack in the manifold, a leaking header pipe-to-exhaust manifold connection, or a leak in the other exhaust system components, including the muffler. I would check these things first.

SIZE DOESN’T ALWAYS MATTER

I bought a 1943 WWII Chevy cargo truck. It is complete except the transmission istaken out. A guy at a wrecking yard says that a transmission he has in a 1946 GMC half-ton pickup is the same and will work in my truck. But my truck is a lot bigger. Even if it fits would it wear out fast? —Martin

It sounds like you bought a Chevrolet G-506. General Motors used the same 4-speed spur gear transmission in half- up to two-ton trucks from the 1930s into the late 1940s, so the one in the ‘46 pickup will probably fit your truck... though you may have to change the tailpiece. Assuming the pickup wasn’t abused, its transmission is probably in much better shape than one from a heavier vehicle, because it didn’t work as hard. Those transmissions were designed to use 140 weight oil. Buying a manual for your Chevy will help you maintain and care for it.

ALUMINUM MUTTS?

Did MUTTs ever come with aluminum bodies? —J. Tanner

At least one prototype (XM151E) MUTT was built by the Ford Motor Company in the early 1950s and evaluated by the U.S. Military. However, since a steel body was not only easier and cheaper to manufacture, but also met the military’s weight specifications, production MUTTs came with steel bodies.

COIL CRACK-UP

I have had my M151 for about six years. It is 1962 and was cut and welded but otherwise stock. I got a truck load of spare parts when I bought it. This has saved me a lot of money. I got three extra ignition coils when I bought it and all of them have cracked on the mounts. Is there a special way to mount them so I’m doing it wrong?—J.T.

I’d guess you have the early coils, which had a tendency to crack from vibration. The military advised checking the mounting screws once a week for looseness, but then a sturdier coil was developed. Install a newer style coil and you shouldn’t have any more crack-ups.

WHAT’S A CARBURETOR?.

I’m 22 and new to the HMV hobby. I just bought a 1963 M37. I thought I knew a little about cars, but this is the first vehicle I’ve had with a carburetor. The engine runs okay but idles rough. I adjust the idle valve on the carburetor when I start the truck and it idles fine. But then after driving, it idles rough again. Could this be an air or vacuum leak?— Tim

Possibly. However, based on what you’ve told me, my first guess would be that you’re adjusting your carburetor for a smooth COLD idle, which is why it doesn’t idle as smoothly after the engine warms up.

Unlike the electronic fuel-injection used on the vehicles of your generation, a carburetor is a rather primitive thing and you have to get to know that particular carburetor on your M37. Since most of your driving will be done with a warm engine, set the idle adjustment so the engine idles best when warm and use the choke to correct a rough cold idle. After you get to know your truck you can experiment with splitting the difference between the smoothest cold idle and the smoothest warm idle. And welcome to the hobby!

Send your favorite Tech Tip or question to Steve Turchet
c/o Military Vehicles Magazine
700 East State St., Iola, Wisconsin 54990-0001, USA,
or e-mail militaryvehicles@krause.com.