by Steve Turchet
There are probably as many reasons for owning an historic military vehicle (HMV) as there are individuals who own them. The experience means different things to different people. For me, the reason for owning an HMV is driving it. I think anyone who hasn’t cruised a desert back road on a warm moonlit night in their jeep, MUTT, M37, M715, or most other HMVs with the windshield down has really missed something...besides the occasional bug in the face. I also think that owning an HMV should be fun. A breakdown in the field, however, can change that fun into plain agony — if you aren’t prepared.
HMVs ARE SIMPLE MACHINES
I learned many of these trouble-shooting procedures and repairs the hard way during my jeep summer. One of the most important lessons was: An HMV owner must be self-sufficient when it comes to tools and spare parts, as well as possessed of a good basic mechanical knowledge in regard to trouble-shooting and repairing their vehicles.
Let’s assume you’re going to take your HMV on a trip. Maybe it’s only fifty miles to a swap meet via the Interstate, or maybe you want to spend a weekend fishing at some remote mountain lake, or perhaps you’re going out for a month exploring ghost towns in the desert. No matter where you’re going, you’ll probably be traveling in a vehicle that is forty, fifty or maybe sixty-plus years old. Even the most basic replacement parts such as water and fuel pumps, generators, starters and often even a head lamp bulb, won’t be easily found along the way.
To some degree, this disadvantage is offset by that fact that most common HMVs are simple machines that are easy to work on with basic tools. What isn’t there can’t go wrong, and as long as your vehicle is in good shape to begin with there shouldn’t be a lot that breaks on a trip that can’t be fixed or at least be patched together by an average person with a basic tool set, some on-board spare parts, and rudimentary mechanical skills. Adopt the “P” principle: Proper Planning Prevents Pee-Poor Performance.
As applied to most common HMVs, this means that every dollar and hour spent on preventive maintenance at home will usually save you ten times that much in money and hours in the field. Having spare parts and tools aboard your vehicle can often mean the difference between a living a dream or enduring a nightmare; and most people who have ever broken down on a freeway and had to call a tow-truck will probably agree.
SOONER OR LATER, YOU’LL HAVEA BREAKDOWN
One second you’re been rolling along in your HMV, looking forward to a hot meal and a shower. But then, you are coasting in eerie silence on an almost deserted highway.
If your engine should suddenly quit like this, and you’re not on a steep downgrade, step on the clutch and start looking ahead for a safe place pull off road while you’re still moving. On an outback trail, it won’t matter much where you stop, though you don’t want to end up blocking the trail—even if only three vehicles a year use that road, they will all show up if you’re blocking it!
On a highway or freeway your choice of stopping places could mean the difference between having the time you need to get your vehicle going again or an overpriced tow to a scam-joint garage. If you were on a downgrade or a level stretch of road when your engine quit, you might have time for a few quick tests while you’re still in motion. Momentum, like battery power, should always be used to best advantage. Once it’s gone, it’s hard to replace.
DIAGNOSING THE PROBLEM
Basically, a gasoline engine needs two things to run: Fuel and ignition. It may help to visualize your fuel and ignition systems as chains of components, each chain having a beginning and an end.
Your fuel system chain begins with gas in the tank and ends at the carburetor, while your ignition system chain begins at the battery and ends at the spark plugs. You can usually figure out what is wrong by working along the chain of components step-by-step.
If you follow these procedures in order instead of randomly skipping around (and assuming you’ve taken the advice in regard to spare parts and tools) you will usually be able to get your vehicle going again fairly soon. It’s okay to trust your instincts up to a certain point—such as checking to see if the coil wire came loose or a fuel line broke—but beyond these hunches, it will almost always save you time and frustration if you track down the problem in a logical order using step-by-step test procedures. You should begin this testing while you’re still in motion.
First, how did your engine quit? If it sputtered, popped, backfired, or made sucking or strangling noises, there’s a good chance your problem is fuel. You might say, “Duh!” but look at your fuel gauge. You may have been day-dreaming when you passed that last gas station, or you might have one of those gauges that reads one-quarter for ages then suddenly drops to empty. If your gauge reads empty, say the four-letter word of your choice, shut the ignition switch, pull off the road and stop.
Check for any fuel leaks, then break out your spare five-gallons of gas and you’ll probably be on your way in minutes. If you have simply run out of gas, it will usually help your engine to start faster if you pour a little gas down the carburetor throat before using the starter.
On the other hand, if your gauge shows you have plenty of gas, leave the ignition switch on, pull out the choke and let out the clutch. If the engine restarts, runs a few seconds and then quits again, you almost certainly have a fuel problem, and you have narrowed the field at least fifty percent because now you know it’s probably not an electrical malfunction.
Once in a while, you might find that by pulling out the choke your engine not only restarts but tries to keep going. This is still usually a fuel problem—though it can also be electrical— but experiment with various choke positions until you find the minimum choke at which the engine will run.
Many times you will be able to reach the next off-ramp, town or gas station by nursing your engine along this way... or at least a good place to stop and find out what’s wrong. Occasionally you will even find that after a few miles you can push the choke all the way in and continue on as if nothing bad had happened.
The most common cause of this is a small amount of water in the gas, and a little of that water either partially clogged the fuel filter or was sucked into the carburetor. If your engine returns to normal operation, stop at the next gas station, check the fuel filter, then fill up the tank.
The other most probable cause would be a weak or dying fuel pump, whether mechanical or electric. If this problem happens again a little farther down the road, and you find no water in the system, your best move would be to install your spare fuel pump and see if that solves the problem.
About the only other reasons an engine would only run with the choke partially closed, would be a vacuum leak or a small leak in the suction side of the fuel system. If, in a situation such as this, you smell raw gas, then shut off the ignition as well as your lights (if safe to do so) and stop immediately. This almost always means a pressure leak in the fuel system — usually in the engine compartment. You could have a fire.
On the other hand, if, and in spite of pulling out the choke —and even if the engine did momentarily restart — it quits again, turn off the ignition switch and find a good place to stop while you’re still rolling. If you’re on a freeway or well-traveled road, get as far off the shoulder as possible and set out your breakdown triangles. If you have to stop partially on the roadway, put out a flare... but if you smelled raw gas then light and place that flare well away from your vehicle where leaking gas can’t reach it. If this has happened at night, remember that battery power is like money in the bank... don’t waste it. Turn off your lights, or at least switch to parking lights. Break out your tool box, and we’ll get back to you in a minute.
Let’s imagine this situation again, back to where you were driving along and your engine quit, only this time it either simply shuts off like you flipped a switch or starts backfiring. Try jiggling the ignition switch or key. Do not turn it off and on because this can make a huge backfire that can blow a muffler apart. Just jiggle the switch lever or key a bit.
If your engine either restarts or begins to run normally again, you might have a bad switch, one with worn or burned contacts inside, or loose terminals on the back of the switch. On some HMVs you might even find that you accidentally bumped the switch lever with your knee or a fold of your parka and halfway shut it off.
If the engine restarts or runs all right again after jiggling the switch, you should still stop somewhere and check the switch, including the terminals on the back. If these feel hot, there’s a good chance they were either loose or corroded. Either will cause high resistance, which produces heat. If the terminals are clean and tight but the switch itself is hot, it should either be replaced or temporarily bypassed with one of your test leads until a replacement is found.
If your engine doesn’t respond positively to jiggling the ignition switch, and/or keeps backfiring, shut off the switch, put in the clutch, and find a good place to stop. This time you can be almost certain that you have electrical and not fuel problems.
Because I want to make these test procedures as clear as possible, I’m only going to cover fuel system problems in this issue. We will tackle electrical malfunctions in the next.
The fuel system is usually the simplest to trouble-shoot and repair, so if there is the slightest question in your mind of whether your problem is fuel or electrical, then always start with the fuel system.
DIAGNOSING THE FUEL SYSTEM
You’ve found a safe spot to pull off the road. You’ve shut off the ignition switch and lights, and set out your breakdown triangles if necessary. Assuming you don’t smell raw gas and/or there’s no gas dripping from under the vehicle, there is one simple test you can perform to ascertain, almost without a doubt, whether your problem is fuel or ignition.
Pour a little gas down the carburetor throat and try to start the engine. If it starts instantly but only runs a few seconds, then makes strangling sounds and quits again, chances are 99 to 1 that you have a fuel problem.
First, make sure there is gas in the tank. Fuel gauges can be inaccurate, especially early M-series models. Depending upon what kind of HMV you have, you can usually either look down the filler pipe (need I say don’t light a match to see by?), or poke a stick or a wire all the way to the bottom to check the quantity. Does there seem to be plenty of gas left? If so, check the fuel filter for water or some kind of clog, maybe rust flakes.
Water in the gas is pretty common for many HMVs because they sit a lot. Temperature changes cause condensation to form in a partially empty fuel tank, so the best prevention is to keep the tank full at all times. Since water is heavier than gasoline, the water collects in the bottom of the tank and can usually be removed by draining.
The fuel pick-up tube usually doesn’t go quite to the bottom of the tank to avoid picking up water, so a considerable amount of water can collect before causing problems. However, the sloshing of fuel on a long trip or a rough back road causes the water to partially mix with the gas so that slugs of water will be sucked into the fuel lines where it will again settle to the lowest points, such as fuel filter and fuel pump bowls, and the carburetor float chamber if it makes it past the filter. A warm and steadily-running engine out on the road will tolerate a considerable amount of water, which will generally show up as an occasional miss, stumble or sputter, but if an extra large slug of water clogs the filter or reaches the carburetor, it can kill the engine.
If water is present in the fuel filter, then drain the bowl and blow out the filter element or replace it with your spare. Also check the fuel pump bowl and filter screen, if so-equipped. If your vehicle’s carburetor has a drain plug on its float bowl, remove it—being careful of gas pouring out on a hot manifold. Water in the gas will show up as bead-like shapes.
Reinstall the plug, then drain a little gas from the fuel tank into a suitable container, such as a soda can or beer bottle, to check for more water. If there is water, wait about fifteen minutes to give it a chance to settle to the bottom of the tank, then drain it out. Pour in your spare five gallons, plus a little down the carburetor throat, and restart your engine. You should be on your way.
If there wasn’t any water in the filter, fuel pump, or the carburetor float bowl, and your vehicle has a mechanical fuel pump, put your vehicle in neutral with parking brake on. If you have a friend along then he or she can work the starter for you. If you’re flying solo and your vehicle has a floor pedal starter linkage, you should be able to figure out a way to activate the starter from under the hood with a hammer handle or stick for a lever. For starters with solenoids, use one of your test leads to jump the terminals. If you’re wearing a ring or a watch, take it off. Keep your fire extinguisher within easy reach.
Disconnect the fuel line at the carburetor: this is the pressure side of the system so beware of gas squirting out on a hot exhaust manifold. Use a container to catch any gas. Now, with the ignition switch off, crank the engine over a few times to see if any gas squirts out of the line. If, after cranking the engine for about ten seconds, nothing squirts out of the line—and you know there is plenty of gas in the tank—you might have a bad fuel pump, or there might be a clog in the fuel line between the pump and the carburetor.
Disconnect the line from the pump and blow out the line. If it’s solidly clogged, use a piece of your bailing wire to ream it out. Then reconnect the line to the pump and crank the engine again, checking for gas at the carburetor end. If gas now squirts out, reconnect the line to the carburetor, start the engine, and you should be rolling again. If there was no clog in the line between the carburetor and the fuel pump, then the fuel pump might have failed, or there may be a suction leak or a clog somewhere in the fuel line between the filter and the tank, and we will get to that in a moment.
If your vehicle has an electric fuel pump, you can dispense with cranking the starter and merely activate the fuel pump using your test leads and leaving the ignition switch off. Some MUTTs have a safety switch that kills the electric fuel pump at low engine oil pressure, so be aware of this if you have such a vehicle. Electric fuel pumps make sounds when they’re running, so no sound obviously means they’re not working. Silence usually indicates the fuel pump has failed, but of course you have a spare...Don’t you?
You should check to make sure your test lead is hot and the fuel tank itself is properly grounded (if your fuel pump is inside the tank). If the pump is external, check to be sure it’s properly grounded to the vehicle’s frame or body. If the pump makes noise but no gas squirts from the line at the carburetor, there might be a clog between it and the fuel filter.
Try blowing or reaming out the line. If the line is clear, and your fuel pump is inside the tank, remove the pump and check to make sure its inlet isn’t clogged. In rare situations the pump will make noise but still not pump fuel, in which case you’ll have to replace it.
With your spare pump installed, activate it, listen to make sure it’s running, then check that fuel now squirts out of the line at the carburetor. If it does, then reconnect, start the engine, and you should be on your way.
Back to HMVs with mechanical fuel pumps: if you know that the pressure side of fuel system is clear (the line between the pump and the carburetor) then either the pump has failed or there’s suction leak or clog between the pump and the fuel tank. Disconnect the line at the suction side of the pump, remove the fuel filler cap, and blow into the line at the fuel pump end. If you can’t reach it, then clamp on your spare fuel hose and blow into that.
Blow hard! You should hear a bubbling sound back in the fuel tank. If your face gets red and you hear no bubbling, or the line is obviously clogged, you will have to work back through the line, or lines, disconnecting whatever fittings there might be, until you find the clog. In rare cases the pick-up tube inside the fuel tank is clogged with rust flakes or something like a leaf, insect, or a bit of cork from the fuel gauge float or the gauge sender gasket.
If you did hear bubbles in the fuel tank when you blew into the line, now suck on the line to see if you can get a mouthful of gas. This generally means you don’t have a suction leak, and usually indicates that the fuel pump has failed. Replace it with your spare, check to make sure gas squirts from the line at the carburetor when cranking the engine, then reconnect the line and you should be going again.
If you don’t have a spare fuel pump, you should be able to rig up a siphon feed from your gas can to the carburetor using your spare fuel hose. The bottom of the can must be above the top of the carburetor. Usually this means attaching the can to the vehicle’s cab or windshield frame. This may look tacky, but it should get you to the next town or gas station... then you’ll find out how much cheaper and more convenient it would have been to have a spare pump with you. Of course, you can use the same procedure for vehicles with electric fuel pumps that have failed.
If you find a fuel line is cracked, broken or was squashed somehow, you can patch or bypass the bad spot with a section of your spare fuel hose. Remember, clamps can be made from bailing wire or nylon electrical ties.
Another fuel system problem you may encounter is vapor-lock. Lots of folks under forty who were raised with cars having fuel injection haven’t a clue what this is.
Basically, your engine will sound and act as if it’s running out of gas and make strangling or sucking sounds in the carburetor throat. Vapor-lock is caused by the fuel lines and/or the fuel pump getting so hot that the gasoline turns to vapor, which the fuel pump can’t pump and the carburetor can’t feed to the engine.
Some HMVs such as the M715 are especially prone to this on hot days because they have poor air flow through the engine compartment (my M37 also did it several times on a hot day in Alberta, Canada). This problem is compounded on hot sunny days if your vehicle is painted OD, because this color absorbs instead of reflecting heat and will turn your engine compartment (as well as your vehicle’s cab) into an oven.
If you suspect vapor-lock, pour a little gas down the carburetor throat and try to start the engine. If it starts okay but only strangles and dies again, you probably do have vapor-lock. About the only fix is to raise the hood and wait for things to cool down.
Sometimes wrapping the fuel pump and lines with wet rags will help. Remember to remove the rags before setting off again. On some vehicles, you may be able to reroute the under-hood fuel lines to keep them away from heat sources such as exhaust manifolds, cylinder heads and exhaust pipes; and keep in mind that OD is not the best color for a vehicle in the desert.
IT TAKES JUST A SPARK
But, after all that trouble-shooting, you still can’t start the truck? The next obvious thing to check is ignition system. As with fuel systems, it will usually save lots of time and frustration if one follows the suggested steps in order instead of relying on hunches or guesswork. These procedures may also come in handy some morning at home when your HMV won’t start.
Since we’re dealing with the most common HMVs, there are two basic types of ignition systems to diagnose and repair. The first type is used on virtually all pre M-series vehicles dating back though and before WWII. These systems are the same types used on civilian cars and trucks of the period, and are the simplest to troubleshoot and fix. Their voltage is usually either 6 or 12, and just about all of their tune-up parts — points, spark-plugs, condenser, rotor, distributor cap and ignition coil — can often be found at well-stocked auto or truck supply houses, while complete distributors may still be located at older wrecking-yards, especially those in rural areas.
The second type is the M-series 24-volt waterproof ignition system common to HMVs such as the M38, M38A1, M151, M37, M715, M2ll, and early M35s. This system is more difficult to diagnose and repair in the field because both the ignition coil and distributor are combined in one waterproof unit... often called the igniter. Field testing such a system presents more of a challenge because the igniter must be fully assembled to function. Trouble-shooting these systems is often a matter of replacing doubtful parts until the engine starts again. Also consider that just about every component of an M-series 24-volt ignition system is Government Issue and, unlike the older WWII systems, there are almost no civilian counterparts... except sometimes the points, condenser and/or rotor. It should therefore be apparent why spare parts need to be carried; tune-up parts (at least) for short trips, and major components such as a spare starter, generator and voltage regulator when traveling far from home or into the wilds.
There is a third type of ignition system one may sometimes encounter on common HMVs: this is when someone has cobbled together a mutant system using both civilian and military M-series components. While most dedicated HMV owners would have changed these systems back to original, there may come a time when one is stranded somewhere and will have to create a mutant system to get their vehicle going again. More on such systems later.
START WITH THE OBVIOUS
Let’s go back to our problem truck where we were cruising along a highway and the vehicle’s engine quit. Using the procedures to check the fuel system, we have determined that the problem isn’t there.
Just like our vehicle’s fuel, it is best to think of theignition systems as a chains of components, having a beginning and an end and all the links vital in between. While a fuel system begins at the tank and ends at the carburetor, an ignition system begins at the battery and ends at the spark plugs. So lets get our HMV mobile again. Remember, do things in order.
The first thing to check is this: Are you getting a spark at the spark plugs? Disconnect a spark plug wire at any plug — number one at the front of the engine is usually the most convenient —and with the ignition switch on, hold the wire’s tip about a quarter of an inch from a known ground such as a cylinder head bolt or the generator mounting bracket and crank the engine with the starter to see if a spark jumps. Naturally you’ll be holding that wire by its insulation or with insulated pliers or you may jump, too. Being bitten by the spark is usually harmless, if unpleasant, but the shock can make you bang your head on the hood or drop your hand on a hot exhaust manifold.
While you may have heard people talk about “strong blue” or “weak yellow” sparks, any spark capable of jumping a quarter-inch gap is sufficient to run the engine. If you do get a spark in this first test, then most of the time you do not have ignition system problems and should re-check the fuel system... although the distributor might have come loose, which could have messed up the timing. Check the distributor’s mounting to make sure it’s tight. Even if you get a spark from one plug wire, check several more wires because this will eliminate the possibility of a carbon track in the distributor cap: if only one spark plug wire sparks, this might be your problem.
Use care when removing the spark plug cables on M-seriessystems because the porcelain tips and rubber ends are delicate and easily broken. If the tip sticks within the spark plug or in the igniter cap after you have unscrewed the nut, then use WD-40 or something similar and gently work the tip out of the plug or cap or you might break it off.
For pre-M-series (civilian type) wires, never pull on the wire itself but grip its metal or rubber tip. This is doubly important if your vintage HMV’s original type metal core wires have been replaced with latter-day carbon or fiberglass core wires, or you have a more modern CUCV, because the core is easily broken and then will not pass electrical current to the spark plug.
Likewise, when reattaching the plug wire or cable to the spark plug, distributor or igniter, spray it with WD-40 or smear it with dielectric grease, and be careful not to cross-thread the M-series cable nuts on the spark plug or igniter cap. If you find that an M-series cable tip is already broken, it might have been shorting, causing the plug to misfire, in which case replace the cable with one of your spares. If you don’t have a spare cable, you’ll have to get creative with electrical tape or maybe a bit of a plastic pen barrel to re-insulate the tip.
If you did get a spark from two or more wires but your engine won’t start — and you’re absolutely sure the problem isn’t in the fuel system — then remove the spark plugs and look at them. They may be oil-fouled, wet with fuel from flooding (a fuel system problem such as a jammed carburetor float or needle valve) or the gap may have burned too wide. Another possibility is that you’ve been using spark plugs which run too hot — especially if you’ve only been driving your HMV on short trips around town — and now these “hot plugs” have burned out from being run at highway speeds all day. If so, then replace them with your spares. If the plugs are only dirty, then clean them with your emery cloth or wire brush, re-gap, and reinstall them. If that was your problem, you should be on your way again.
On the other hand, if you don’t get a spark at any plug wire, the next thing to check is for primary voltage (6, 12, or 24) at the ignition coil. However, if your HMV is a pre M-series type, check to be sure that the coil’s secondary wire — the thick one that runs from the top of the coil to the center distributor terminal — is firmly attached at both ends, especially on coils that are mounted upside-down as on some CCKWs and Chevrolet G-506s. Also make sure that the two smaller wires — one coming from the ignition switch and the other going to the distributor—are unbroken and firmly attached.
Make sure that the coil is firmly gripped in its mounting bracket and the bracket is tight and grounded to the engine. You can ascertain that the coil is indeed grounded by trying to spark its case with your test lead or by using your probe tester. If you find the coil isn’t grounded, fix the problem and you might be on your way.
Always turn off the ignition switch after performing a test and getting ready for the next. Leaving the switch on when the engine isn’t running can burn the ignition points and/or damage the coil.
If a loose coil wire or bad coil ground wasn’t your problem, break out your test leads... the ones I suggested you make, about six feet long with alligator clips at each end. For pre M-series vehicles, clip one end of a lead to the coil’s primary input terminal, which comes from the ignition switch — NOT to the other small terminal that connects to the distributor or you could damage the coil and/or condenser—and turn the ignition switch on.
Lightly brush the free end of the test lead across a known ground. If it sparks, this means you’re getting primary power to the coil from the ignition switch and that part of the system should be okay. Alternatively, if you have a probe tester, clip its wire to the coil’s input terminal and touch the probe to a known ground to see if it lights up.
On M-series vehicles, you will have to unscrew the primary wire from the distributor to perform this test, clamping the test lead or inserting the probe into the little female connector within the primary wire’s terminal. Make sure you have a good connection. Then, with the ignition switch on, try to spark the other end of the lead, or connect the tester’s wire to a known ground to see if it lights.
If you don’t get a spark, or your tester doesn’t light (be sure to test your tester occasionally), it means that there isn’t power coming from the ignition switch, which may indicate a bad switch or loose connections as discussed,. A simple way to confirm this on pre M-series systems, is to connect your test lead to a known power source, such as the battery, and touch the other end of the lead to the coil’s primary input terminal. It’s normal to get a small spark here if you do this.
Now, with the lead connected between the battery and the coil, try to start the engine. If it starts, then you likely have problems with the ignition switch, its connections, or other wiring behind the dashboard; but at least you can get your vehicle off the highway and to a better place to work. You might even drive it to the nearest town hot-wired like this, but if you do, remember that there’s a problem in your wiring somewhere and be alert for sparks, smoke, or the smell of fried wires. And of course you won’t forget to disconnectyour hot-wire once you’ve gotten where you want to go.
On the other hand, if you are getting power to the coil from the ignition switch, then here’s where we have to separate the WWII-style system from the M-series systems. We’ll start the the WWII types.
Turn the ignition switch off. Make sure the distributor is securely mounted to the engine and hasn’t come loose and slipped timing. Then remove the distributor cap. Examine both the cap and the rotor to make sure their contacts and terminals aren’t burned, broken, or eroded away. If so, replace them with your spares and that may get you going.
If the cap and rotor look okay, check to be sure the distributor’s drive shaft, drive key, or coupling pin isn’t broken or sheared. Try to turn the rotor by hand...don’t use excessive force or you might break the rotor. If you can turn the rotor more than about a half an inch in either direction (or all the way around) then check to make sure its drive tang isn’t broken where it fits into a notch on the top of the distributor shaft. If the tang is broken, make sure the distributor cap fits properly on the distributor body and the mounting clamps hold it securely in place. A loose cap will often break a rotor. Then install your spare rotor, and you should be going again.
If you are able to turn the rotor shaft more than about a half an inch (or all the way around) then the distributor drive key or coupling pin has probably sheared and you will have to pull the whole distributor out of the engine. More on that later.
If the distributor shaft and rotor seem okay, take the coil’s secondary wire (the thick one) out of the distributor cap, leaving its other end connected to the coil. Turn the ignition switch on. Hold the coil’s secondary wire about a quarter-inch from a known ground just as you did with the spark plug wire in the first test. Then, with a small screwdriver, pencil, pen, twig, whatever, open and close (“break”) the distributor points. If the points were already open, up on a lobe of the distributor cam, turn the ignition switch off and rotate the engine, either by hand or with the starter, to close the points. Then turn the ignition switch back on.
Normally, when you break the points with a pencil or screwdriver, there should be a small spark at the point contacts and the coil’s secondary wire should spark strongly at the ground. If this happens, it usually means that both the coil and the condenser are okay, but the points could be dirty, burned, or out of adjustment. Turn the ignition switch off. (Incidentally, if you break the points with your fingertip instead of a pencil or screwdriver, you may get a small shock.)
The point gap gets smaller (closes up) over time as the rubbing block wears away; and on vehicles that sit a lot the distributor cam may get rusty, which will rapidly wear down the rubbing block. The cam may be polished with fine crocus cloth—be sure to clean all the grit out of the distributor afterward—and you should always use a little cam lube grease to prolong the life of the rubbing block. The point contacts will eventually burn, even in normal operation; however this burning will be drastically accelerated if the ignition switch is left on when the engine isn’t running. Another common cause of burned points is a failing or failed condenser (sometimes called a capacitor) or the wrong condenser for your vehicle.
Clean the points now, either with a points file or with crocus cloth, then re-set the gap with the contacts fully open on a cam lobe. If you don’t have a feeler gauge — and shame if you don’t — a paper matchbook cover will give you a point setting of about .020”... a setting at which most common HMVs will run. Install the rotor and distributor cap, and put the coil’s secondary wire back into the cap’s center terminal. Turn the ignition switch on and try to start the engine. If it starts, then dirty, burned, or out of adjustment points were the most likely problem... though the condenser may have failed or be failing.
If, when performing the test of manually breaking the points, you get a small spark at the point contacts but no large spark from the coil’s secondary wire, and you’re sure the coil is properly grounded to the engine, then it’s just about certain you have a bad coil. Install your spare coil.
An ignition coil is like a light bulb: 99 percent of the time it either works or it doesn’t and there’s no way to fix it, so always carry a spare. Make sure that the polarity of its two small wires are correct... on negative-ground systems (most commonU.S. MVs, where the battery’s negative post is grounded) the wire from the ignition switch goes to the coil’s positive terminal while the small wire to the distributor is connected to the coil’s negative terminal.
On less common positive-ground systems (some Fords, IHCs, and early model Land Rovers) where the battery’s positive post is grounded, the small coil wires are connected just the opposite. Your engine will still run if the coil’s polarity is reversed, but it won’t run well and will be hard to start because the spark at the spark plugs will be jumping from the ground to the electrode instead of from the electrode to the ground.
If neither the points nor the coil’s secondary wire spark when manually breaking the points, turn the ignition switch off and check to make sure that the small wire running from the coil to the distributor is unbroken and firmly attached at both ends. You can also hook up one of your test leads to double-check this. Also check the insulator block — usually bakelite, fiber or plastic — where the wire connects to the distributor body. If this insulator is broken or loose, the wire from the coil might be shorting to the distributor body, and nothing will spark. If you find this insulator broken, you can usually make a temporary replacement from a plastic pen barrel, a bit of rubber, or simply wrap the little bolt with several layers of electrical tape where it passes through the distributor body.
STILL NO SPARK FROM POINTS OR COIL?
If the points are clean and properly gapped, you may have a bad coil or simply a bad condenser. A shorted condenser will usually prevent both the points and the coil from sparking. With the ignition switch off, replace the condenser. While you’re doing that, check that any other wire down inside the distributor, such as the one going to the condenser, is unbroken and firmly attached. Turn the ignition switch on and try the spark test again by manually breaking the points. If both points and coil now spark, then the condenser was the problem and you’re on your way.
If, after replacing the condenser, you still can’t get a spark at the points or from the coil’s secondary wire, then it’s probably a bad coil. Turn the ignition switch off. Replace the coil, checking for proper polarity, and you should be going again.
Back-tracking a bit, if you found the distributor shaft, drive key or coupling pin was broken, then your field ingenuity will be tested because you will have to pull the distributor out of the engine to see if you can fix it; either that or install your spare distributor... if you were prudent enough to have one along. Before you pull the distributor, mark the position of its body in relation to the engine, which will make it a lot easier to re-time the engine, and carefully number all the spark plug wires (duct tape makes good markers, and you can write on it with pen or pencil) as well as the distributor cap terminals so you will know the correct firing order.
Congratulations if you have a spare distributor with new points, condenser, rotor and cap all ready to install! If you do, you will probably save yourselfa couple hundred-dollar towing bill and / or a long lonely night stranded on the roadside. If you have that spare, you will save many wasted hours trying to locate a replacement in some unfamiliar town or waiting for a buddy to send or bring you one. You can install it in minutes and be back on your way!
But, f you weren’t as well-prepared, you might still be able to fix your broken distributor in the field. Distributors vary with vehicle type of course, but most have some sort of coupling pin to connect the drive gear to the rotor drive shaft, and it’s not uncommon for this pin to loosen with age and break.
If this happens, the pin can usually be replaced with a nail or small machine screw or even a piece of heavy wire from that fence along the road or freeway. Peen the ends of the new pin with your ball-peen hammer to secure it in place, reinstall and time the distributor, and you should be mobile once more. Keep in mind that your field-repair pin probably won’t last very long.
If you find that your distributor is damaged beyond a broken connector pin, you will probably have to have your vehicle towed to the nearest town and try to find a replacement. Of course the circumstances and situations will vary: You may have another distributor at home (lot of good it does you there) that your spouse or a buddy can send or bring to you.
I have been very few places in this world where there isn’t at least one car or truck wrecking yard within fifty miles... even an “unofficial” one in some farmer’s field. If you have a WWII or pre M-series HMV, then you should know that practically any distributor for a Dodge, Chrysler, Plymouth, or Fargo 230 or 260 engine will work in your Dodge truck, whether three-quarter-ton WC, or the earlier half-ton and pre-war VC models. These civilian distributors can also be adapted to your M37... more on that later.
For CCKWs or WWII Chevy trucks, just about any civilian distributor from a Chevy 216 or 235 engine, or a GMC 228, 236, 248, 270, or 302 will work. Even if your HMV is a Studebaker, Ford, or IHC, you can usually find a distributor on a civilian car or truck of similar vintage. Also keep in mind that the parts of most older distributors will interchange, so with a little field ingenuity you can usually cobble together something that will work.
ROADSIDE TESTS FOR M-SERIES VEHICLES
Now we’ll move on to the same roadside tests on M-series vehicles with 24-volt waterproof systems. Since both the ignition coil and distributor are sealed within the igniter, which must be assembled to function, there aren’t many tests you can make as simply as with the WWII-style systems where you can check things out with the distributor cap removed. Most of the time on M-series systems you will replace components with your spares until your engine starts again.
If, after checking for spark at the spark plugs in the same way we tested the WWII-style system, check to make sure that power is getting to the igniter from the ignition switch by removing the primary wire from the igniter and testing for power (with the ignition switch on) with your test lead or probe tester. If you are getting power, then turn the ignition switch off and remove the top of the igniter.
You will usually see a coil capacitor and a resistor in addition to the condenser found in WWII-type distributors. Check to make sure the rotor isn’t broken or the connector pin on the drive shaft isn’t sheared in the same way we checked the older system components. If the cap and/or rotor are burned or eroded, replace them with your spares and try to start your engine. If that was the problem, then you’re on your way.
If the engine won’t start, then turn off the ignition switch, clean and re-gap the points, and also check that the little spring in the distributor cap which contacts the coil’s secondary tower is making a good connection. If the engine still won’t start, you should probably install your spare condenser and coil now. As mentioned, many 24-volt igniters also have a resistor and/or coil capacitor, and while theseare usually very long-lived, one should still carry spares.
If the engine still won’t start after replacing the condenser and coil, try replacing the resistor and/or capacitor as well. If this doesn’t get you going, then try installing your entire spare igniter ... which, of course, you have already tuned-up and tested at home. If that doesn’t work, then at least be consoled by knowing you have done just about all you can in the field.
About your only option is to create a mutant system using civilian components as suggested in the illustration. As already mentioned, many points and condensers, and sometimes the rotors, in 24-volt igniters have civilian counterparts and may be matched by appearance at well-stocked auto or truck supply houses... though this may not work at many chain stores where, if a part isn’t on their computer, many clerks don’t have the necessary real-time experience to help you...and also often lack the inclination.
However, the failure of a 24-volt igniter cap or coil, or the igniter itself is a more serious matter, and you will seldom find replacements at any auto store. But, if your vehicle is an M37, M38, M38A1, M715, M211, or Reo-powered M35, you may be able to locate a civilian type distributor, and certainly a 12-volt coil.
It’s simple to install these civilian distributors in place of the 24-volt igniter. Don’t worry about the vacuum advance line on some of these distributors: you don’t need to hook it up. Likewise, you won’t need to hook up your vehicle’s fording vent lines.
Install a 12-volt coil in some convenient place on your engine, and make sure it’s grounded. You can either use your existing 24-volt spark plug cables and waterproof plugs by taping the cables into the civilian distributor cap, or you can use civilian type wires and tape them into your waterproof plugs.
Alternatively, you can replace your waterproof spark plugs with civilian counterparts. You can supply 12 volts to the coil by taking a lead from your vehicle’s “first” battery. If possible, use a coil that doesn’t require a resistor. If your replacement coil has come from a scrapped vehicle, be sure to liberate the resistor as well.
If you find yourself in a situation where your 24-volt coil has failed, you can usually rig up your igniter to run with a 12-volt coil. In fact, a 12-volt coil will fit right in place of the 24-volt coil in the igniters of M211s and M35s, though you will have to shorten the coil’s center tower by sawing or filing some of the insulation away. Disconnect the igniter’s resistor and run the igniter’s input wire directly to the 12-volt coil’s primary input terminal. Likewise, disconnect the igniter’s primary input wire, which comes from the ignition switch, cut the wire, and rig up a lead to supply the igniter with 12 volts from your vehicle’s “first” battery.
YOU SHOULD BE READY TO ROLL!
By now one should surely realize the importance of carrying tools and spare parts aboard their vehicle; and while not all HMVers take their vehicles into the bush or even on long road trips, one should still consider the inconvenience if driving their jeep or M37 down to the local Quickie-Mart and finding it won’t start again.
Even if you have towing service, you can usually do some trouble-shooting and replace a coil or condenser in the time it takes for a tow truck to arrive. You may also discover that many tow companies with smaller trucks designed for today’s cars won’t even want to handle your M37 or M715... and definitely not your Chevy G506 or White Scout Car! If your HMV is larger than a jeep, always make sure the dispatcher understands how large — or at least at large-appearing — it is.
Once again, with a good basic tool set, on-board spare parts — and a little ingenuity — you can almost always get your military vehicle going again when you are stranded “in the field.”