Tech Tips: June 2019 Edition

Where Did It Go?
I own a 1964 Unimog 404. I was checking the oil levels the other day and found the transmission almost empty. I topped it off six months ago, and there is no oil leaking from under the truck. What could have happened to the oil? Is this a leak that only happens when I’m driving? — Matt

If a Unimog transmission output seal leaks, it doesn’t show externally. It leaks down the inside of the drive shaft tube, and overfills the differential.

Parts Is Parts… Not
I saw NOS starter switches advertised online. The seller says they are for M38 jeeps and also M37 trucks. I have an M38 but I thought those switches were different from the ones on M37s. — Les Glinsky

They are different. An M37 starter switch could possibly be modified to fit an early model M38 starter, but most M38s were fitted with updated starters, which M37 switches won’t fit.

T’ain’t So
I am looking at a nice M38 for sale. It looks like in very good condition and drives well. But it has WILLYS on the sides of the hood. The seller says this is because it is a very early model script jeep.” Is that right? — Dave T.

The unofficial term, “Script Jeep,” only applies to early WWII model Ford and Willys jeeps, which came from the factory with “Ford” or “Willys” embossed on the left side of the rear body panel. This free advertising was discontinued by government order later during the war… though not, as some people believe, to keep the enemy from knowing what company built the vehicles.To best of my knowledge there were never any M38 “Script Jeeps,” and I strongly suspect what you’re seeing is an M38 with a CJ hood. You didn’t mention it, but I doubt if there is a cut-out on the right side of the hood for a deep-water fording kit and power plug receptacle. The seller may simply be misinformed, but if the jeep is in good condition and the price is right for you, I wouldn’t let that be a deal-breaker.

They Came In Colors
Did Willys military jeeps come from the factory in any other color but olive drab? — Nick Epstein

During WWII the majority of Willys and Ford-built MB and GPW jeeps came from their factories only in various shades of OD. However, after the war, M38 and M38Al jeeps could be also ordered from Willys in Air Force “Strata” (or “Baltic”) blue, Navy “Haze” gray,” or Marine Corps “Forest” green.

Toasty Toes
Were the heaters for M38 Arctic Kits always mounted on the cowl? — R. McKenzie

The gasoline heaters were. However the water heaters were mounted inside on the floor on the right side of the transmission cover… which made cramped foot-room for the jeep’s passenger.

HMMWV Ownership
As with any vehicle, owners of HMMWVs should do the basic maintenance that all vehicles require: Changing the engine oil and filter; lubricating all fittings; keeping appropriate levels of transmission, brake and power steering fluids; keeping appropriate tire inflation, tread wear, rotations and alignment; as well as general maintenance of the painted surfaces. Air filters should be checked at a minimum of three to six months, and more frequently if the vehicle is operated in dusty conditions.

Hard Work
I bought an early model Reo M35. It is my first big truck, but I have worked on smaller vehicles and jeeps for a long time.

It seems very hard to adjust the brake shoes on this truck. I know that they adjust the same as on smaller vehicles by adjusting them out until you feel the shoes drag on the drum. But it is hard to turn those big wheels. Is there a better way to adjust the brake shoes on these trucks? — Bill Moritz

You’re doing it right, though it is harder to rotate the wheels of an M35 than an M38. Some people remove the drive flange bolts and pull the axle shafts out a little to make wheel rotation easier.

The Right Stuff
I have a 1943 CCKW. The hydrovac unit is giving out. Are there still rebuild kits for these? — Dale

CCKWs and variants used at least three different types of hydrovac units, so you need to determine what type your truck has. Be aware, the unit may have been updated over the years.There are still rebuild kits available for the later units. if you’re good at improvising, you can probably find or make suitable parts to rebuild the older models.

Engine Swap
Is it possible to put a GMC 302 engine from an M211 into a CCKW? I can get a good 302 cheap and the 270 in my CCKW threw a rod. — D.D.

Just about anything is possible if you have the skills and determination to do it. I put an M211 302 in a DUKW — which is a lot more work than installing one in a CCKW.The CCKW bell housing will fit the 302, but you’ll have to find a manual transmission flywheel. The M211 engines have a cast boss on the rear right side that interferes with installing the starter motor, so you’ll have to grind it flush with the block. M211s had electric fuel pumps so there’s no opening in the block for a mechanical pump. However, the M211 302s do have a camshaft lobe for a mechanical pump, so you can make an opening and drill and tap mounting bolt holes (or a good engine shop can) by taking measurements from the 270.These are the major things. The rest are just what you have to do when making any engine swap.

Let It Breathe
Breather vents on axles, differentials, transmissions and transfer cases may look like simple things, but many people don’t know there are important differences. Many breathers are calibrated to certain pressures, and installing the wrong type may cause excessive pressure in an axle, transmission or transfer case, resulting in oil leaks.

Likewise, a clogged or damaged breather may also case leaks. Always keep breathers clean and check them for damage. If replacing a breather, try to be sure it’s the right one, and check for oil leaks after installing.

Tipping Tip
I once bought an M37 that had a broken rear axle shaft on the “long side.” You might think this would be a simple matter or replacement, but getting the broken shaft out of the axle housing was a puzzle — at first.

The “pumpkin” couldn’t be removed with the shaft still inside. Even a strong magnet on a broomstick wouldn’t pull out the shaft. I finally tilted the truck by lifting the opposite side with a forklift and tapped on the axle housing with a heavy hammer. The broken shaft slid right out.

Bearing up
When replacing rod bearings in early model GMC 270 engines, such as used in CCKWs and DUKWs, you should be aware that later model 270s had slightly narrower rod bearing journals. Later model rod bearings are correspondingly narrower. While they will work in the earlier engines, you may want to track down a set of the early model wider bearings, if possible.

But It’s Supposed To Be A 4X4
I bought a nice looking and good running Chevrolet G506 at an estate auction. The truck seems to be all original. I took it out in the desert in sand but when I tried to put it in all wheel drive the front axle wouldn’t go in. What I mean is, it seems to engage, but the front wheels weren’t pulling.

A friend told me the front differential is broken. Could that be it? — K. Morrison

Possibly. I assume you know if the front drive shaft is turning when the front wheels are rotating? If not, jack the front wheels off the ground, and with the transfer case disengaged, turn the front wheels. If the front drive shaft doesn’t turn, it could be a broken differential.However, another — and happier — possibility is the truck’s former owner may have drilled the spines out of the front axle drive flanges to make “free-wheeling hubs” for highway driving. This is simple to check by just removing the flanges. If that’s the case, just buy another set of drive flanges.

Tiger Eyes
Did any early aluminum M-series front lights have amber or yellow lens for the parking and / or turn signals? — Tim Roberts.

Yes, but they seem to be very rare. I’ve only seen one in the flesh, but I have seen photos of M715s with amber lenses. A glass shop should be able make them for you using the clear lens as a model.

Box Set
I know a lot of WWII jeeps were shipped overseas partly disassembled in boxes. Was this only done during WWII? - Max G.

Other vehicles besides jeeps were also shipped this way. There were even twin-packs where two vehicles were packed together in one crate. But, as this photo of an M38A1 shows, this method of shipping wasn’t exclusive to WWII.

Blow Air Tanks Daily
If you’ve just acquired your first air-system-equipped HMV and think this term rather ominous — or colorful — it simply means opening the drain valves on all your vehicle’s air storage tanks when those tanks are under pressure every time you’ve driven the vehicle. Most air system problems can be avoided by following this rule.

Also, as with fuel tanks, condensation can form over time simply because of temperature changes. So, if your HMV sits for long periods without being driven, always blow the air tanks under full pressure after initial start up.

Hot Hubs
I have a Pinzgauer 710. I have noticed that the hubs get hot when driving on the road at high speeds. Should I be concerned? — Dave Barry

One of the disadvantages of gear-reduction hubs or “Portal Axles” as used on vehicles such as Pinzgauers, Unimogs, and HMMWVs is that they generate heat due to friction and are not ideally suited to high-speed operation (though they performed very on Volkswagen Transporters).While it is normal for them to heat up during high-speed highway driving, they should not become too hot to touch. Using top-quality of synthetic gear oil and/or a quality gear oil additive will help prolong their life.

Bring Back The Glow
A common problem with early-production HMMWVs was that they wouldn’t start in cold temperatures. At first, it was thought that the glow plugs were at fault because they were burning out at a rapid rate. In fact, it was reported that the military was replacing HMMWV glow plugs on the average of one every three minutes!

However, the problem turned out to be caused by the glow plug control units. The solution was to replace the early style mechanical controllers with solid-state units.