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Military Vehicles Magazine Tech Tips: Frozen engines, wipers and more

Steve Turchet answers your military vehicle questions.
Tech tips Jeep


The best way I’ve found to break loose a seized or “frozen” engine is to remove the head and fill the cylinders with ordinary brake fluid (not silicone). Let it stand a few days, and the engine will almost always free up. I’ve found that brake fluid works far better and faster than Liquid Wrench, diesel fuel, kerosene, or any other “methods I’ve ever heard of, including on engines with cast-iron pistons. Never hammer on the tops of the pistons, even with a wooden block, to try to fee them. Instead, remove the flywheel cover and use a stout pry bar on the flywheel teeth. Try to turn the flywheel in both directions. You’ll probably find that it will begin to move slightly at first. Then keep rocking it back and forth, and it will go a bit farther each time until the engine is finally free again. Naturally, you’ll change the oil before attempting to start the engine. Remember that brake fluid also removes paint quite well, so don’t spill it on your vehicle’s bodywork.


If your vacuum windshield wipers are getting sluggish, and you know there are no leaks in their hoses or lines — and that your double-acting fuel pump is OK — try disconnecting the hose at the wiper motor and spraying some WD-40 into the motor with the valve (switch) on. Work the motor back and forth with the hand lever or the wiper arm as you do this. You should notice some improvement in the wiper action after this treatment. Also, lubricate the motor’s wiper-arm shaft with a few drops of oil from time to time.


If you’re thinking about converting your 6-volt HMV to a 12-volt system, you should know that this isn’t very complicated. For one thing, 6-volt wiring and battery cables are heavier than on most 12-volt vehicles, so you don’t have to worry about that; and 12-volt generators, voltage regulators and ignition coils are readily available. You do not have to change your distributor, spark plugs and starter. Most 6-volt starters will actually last longer in a system converted 12-volts... but avoid long periods of cranking. Mechanical gauges obviously don’t care what the electrical system voltage is, and most 6-volt fuel gauges will operate on 12-volts, although step-down resistors are available. You can also install a resistor for your heater’s 6-volt blower motor. This usually leaves you with only the headlamps and light bulbs to change from 6 to 12 volts. And yes, 12-volt sealed units are available for WWII-style tail and blackout lamps.


If you ever encounter a situation where the transmission locks up on your early model jeep, immobilizing the vehicle, one thing to check is the nut on the back of the transmission’s main shaft. This is the large nut that holds the transmission output gear in place. If the nut comes loose, the main shaft can move forward and lock up the transmission. Naturally, you must remove the transfer case to check.


A properly fitted fan belt should always be flush with the top of the pulleys, or at least no more than 1/16 of an inch above them. If a belt sits too low in the pulleys, it rides on the bottom and there’s no “V” or wedging to keep it from slipping. The result can be engine overheating, reduced generator output and rapid belt wear. On the other hand, if the belt sits too high in the pulleys, it can become unstable and twist or even jump off.


The temperature rating of thermostats (160, 180, 190, etc.) indicates the temperature at which the thermostat starts to open: It does not mean that your engine will necessarily maintain that temperature. Always carry a new thermostat and gasket, plus the tools to install it, when venturing far from home in your HMV.


Owners of MB, GPW, M38 or M38A1 Jeeps, or their civilian counterparts, are sometimes mystified by an odd little rhythmic “skip-miss” when the engine is warmed up and idling. Assuming you’ve checked all the usual things — tune-up, point setting, carb. adjustment, fuel pump, possible vacuum leaks, etc. — this problem can usually be traced to a valve that’s set a little too tight. Adjust your valves, but try setting them about .002” wider than specs, and this miss will usually disappear.


Q: My 1971 M35A2 is a daily-driver work vehicle. I would like to make it safer and more efficient. Here are some ideas I had: changing out the 6.72:1 differentials and maybe changing gear ratios in the tranny to gain 15 mph to the max speed for highway driving with 9.00 x 20 tires. I want to keep the multifuel engine. Would it be possible to install a selectable differential from a front-wheel-drive unit to the rear-most axle to gain a tighter turning radius and cut down on front tire scrub instead of removing the inter-axle propeller shaft? Do they make LED sealed headlights, front turn signals and interior lights for the 24 volt system? What is the exact MPG for a 13,530 lb. M35A2 with winch, and how could I improve my fuel mileage? How much would lightening the cargo bed help? I would greatly appreciate any input, ideas or advice on how I could achieve the results I want. —William Minton

A: One may accomplish just about anything in the way of vehicle modifications, as long as one has the time, tools, skills...and most of all the money to do them. I once installed a rear Rockwell bogie with an inter-axle differential from a Reo cement-mixer truck into a Reo M35. This eliminated all the problems caused by the stock rear bogie, which does not have an inter-axle differential. I also made a set of free-wheeling hubs for the front axle by drilling the splines out of a second set of flanges — keeping the original flanges for off-road use — and these modifications vastly improved the truck’s overall performance and fuel mileage.

As far as changing the axle differential gear ratios, one would have to do research to find out what alternatives are available... unless you’re wealthy enough to have gear sets custom made. The same would apply to the transmission. One could install a two-speed unit between the transmission and transfer case for additional overdrive — by moving the transfer case back — however this might cause overheating of the transfer case and axle differentials by over-speeding them.

I don’t know what you mean by “selectable differential from a front-wheel drive unit.” The stock M35 differentials are the same, front or rear, and are neither lockable nor selectable. Front axle engagement is via the transfer case, not the front axle differential. If you mean, could you install a front axle assembly in place of the rearmost axle so that the wheels would steer and perhaps reduce tire scrub on turns, I’m sure it could be done; though I suspect that, unless you could add some way to steer or lock the wheels, you might have problems backing up because the rear wheels might cock in the opposite direction from which you wanted to turn.

As far as fuel milage for your truck, that depends upon so many factors that it’s useless to speculate. One can do simple math using the fuel tank capacity and the range given in the vehicle specifications to get a figure of what the military hoped for. The cargo beds on these trucks are already relatively light, so I don’t think that even cutting off the sides would provide a significant increase in fuel mileage. As far as lights, my advice would be to check the ads in this magazine and/or do research on the Web.

There are several great websites for deuce enthusiasts that are full of advice and stories about what people have done with these trucks. However, it’s often best to start with simple modifications. I would suggest first try adding locking hubs to your deuce’s front axle. This should provide some improvement in fuel mileage. So would removing the inter-axle drive shaft for highway use.


Q: I am thinking abut buying a 1942 Willys Army Jeep that is for sale in my town. It will be my first military vehicle and I will restore it. The seller claims that it is completely stock, but the windshield is different from all the pictures I have seen of WWII. The glass is one piece instead of two pieces and doesn’t open up. It also looks too high compared to pictures I have seen. Do you think this is the right windshield for a 1943 Jeep? —George Ferns

A: Probably not. I suspect the windshield is from either an M38 or a CJ3A. Both had one-piece glass that didn’t open, and the corners of the glass were rounded, not square. Other differences are that most WWII jeeps had windshield frames made of round tubing like water pipe, while the M38 and CJ3A frames used rectangular tubing. The M38 and CJ3A windshields are also taller than the WWII models. Hopefully, the seller is only misinformed and not intentionally saying things that are not so. The best way to be sure that any military vehicle advertised as “stock” actually is, is to buy a manual with pictures and compare those pictures with the vehicle in question. Keep in mind that many “stock” HMVs you may see on the Web — or even advertised in this magazine — may not really be stock.


Q: I just bought a 1951 M38A1. According to the data plate the max speed is 55 mph. But there is an old faded stencil on the dashboard that says “MAX SPEED 45 MPH.” Which is correct? —H. Stein

A: For most vintage U.S. military vehicles, such as jeeps or M37s, the maximum permissible road speeds on the data plates could be compared to driving an average civilian vehicle of the same vintage — such as a stock 1940s Ford or Chevy — as fast as the last number on their speedometers. They might do it for awhile, but in most cases their engines would self-destruct in a short time. Many U.S. military vehicles had the type of dashboard stencils you describe added during the 1960s because they were being driven too fast and were blowing engines. If I owned your M38A1 I wouldn’t drive it over 50 mph. Yes, someone may tell you they drove theirs every day for fifty years at 70 mph, but as my dad used to say, “Anyone who says they like a cold shower in the morning will lie about other things, too.”

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