Historic Military Vehicle (HMV) Maintenance

Thousands of books and manuals have been written about repairing, maintaining, and restoring virtually every make, model, and vintage of vehicle from Model T Fords to the newest SUVs. In regard to military vehicles, there are usually several manuals for each type, from WWII jeeps to present-day HMMWVs. Yet, it’s funny that some people will pay thousands of dollars for a jeep, MUTT, M37, or M35, but won’t pay twenty bucks more for the appropriate service and repair manual. While you should always have the manuals that apply to your vehicle, you will probably find that keeping your historic military vehicle (HMV) in good dependable running condition is not always a matter of doing everything by the book. Instead, you will usually find that maintaining a reliable HMV is mostly an ongoing, common sense process of checking things out, performing basic service at fairly regular intervals, and fixing things before they break.

Good HMV maintenance is also a matter of getting to know your particular vehicle. This process should start as soon as you get it home. Squelch that adolescent urge to drive it right away and show it off to all your friends like a teen with his or her first car.

Why? I once bought an M38Al jeep that seemed to be in very good condition and ready to drive. When I checked the transmission I found only rusty water inside...no gear oil at all! Had I given in to the urge to drive it around, I would have destroyed the transmission within a few miles.

Always assume the worst with a newly-acquired vehicle. Assume that the gear oil is low, and/or dirty and worn out, in the transmission, transfer case, and axles. Likewise, the engine oil and power steering fluid. Assume that the wheel bearings need repacking, the vehicle is decades overdue for a lube job, and the brake fluid is twenty years old. Assume that all components, connections, drive belts, hoses, and nuts and bolts are loose. Inspect all the brake lines – the steel ones for rust or damaged spots, andthe rubber lines for cuts, cracks, or old-age.

If your vehicle has a vacuum or air brake booster, inspect it for leaks and deteriorated parts. Check all the universal joints for looseness, and put a wrench on their mounting bolts to make sure they’re tight. Check the tightness of the engine, transmission and transfer case mounts. If a mount is badly deteriorated or broken, it should be replaced before driving the vehicle. Jack each wheel off the ground to check for looseness or roughness of the wheel bearings.

Most common HMVs have drain plugs on the bottom of their fuel tanks. Make sure the plug isn’t rusted in place, then drain a little fuel to check for water. Inspect the muffler and exhaust system for damage and leaks. Also check the engine block to exhaust manifold gaskets for leaks.

With the engine off, grab the fan and try to wiggle it to check for loose water pump bearings. Also check that the fan isn’t bent...a bent fan wears out water pump bearings. If the brake pedal goes more than halfway to the floor the first time you step on it, you may have worn out brake shoes, or shoes that simply need adjustment. Of course, make sure that all the lights, including the service stop light, are working. The same goes for the horn and windshield wipers.

Check everything that uses gear oil, not only the transmission, transfer case, differentials, and reduction gearboxes (HMMWVs and Unimogs), but also the steering knuckles, steering box, and the winch gear case. You should be able to check most of these things in a day. It should give you a good idea of your vehicle’s overall condition. This inspection should also reveal how well – or not – the former owner cared for the vehicle.

Most common HMVs, such as jeeps, MUTTS, Dodge WCs, M37s, M715s, CCKWS, M211s and M35s, are simple machines by today’s standards, and easy to work on with basic tools and home shop equipment. To some degree the same can be said for the M998 HMMWV. While a HMMWV may seem very high-tech compared to a Willys MB, ninety percent of the machine is still basically nuts and bolts.

The concept, “one size doesn’t fit all,” also applies to servicing and maintaining most HMVs. Unless your vehicle is a daily driver and/or is used off-road or for actual work, its service and maintenance should be more a matter of common sense than doing everything by the book...including when to do it.

For example, there are some maintenance tasks that should be performed on every vehicle no matter how much or how little they’re driven. Examples are changing the brake fluid, renewing the engine coolant, and checking the battery water levels.

The reason you should change your vehicle’s brake fluid about every two or three years is conventional brake fluid attracts moisture whether or not a vehicle is driven. (You may also use a vacuum pump or “turkey baster” to empty the master cylinder, then refill it with new brake fluid.)

The question often arises as to whether one should use conventional brake fluid or silicone fluid. The main advantage of silicone fluid is that it doesn’t attract moisture. On the other hand, silicone fluid tends to leak out of a system because it doesn’t swell the rubber parts in the master and wheel cylinders (at least not as much) as conventional fluid. Silicone brake fluid is more expensive than conventional types, and may be harder to find. Silicone fluid may give a spongy feel to the brake pedal, and is often not recommended for the types of vacuum or air-assisted brake systems found on common HMVs, such as the Chevrolet G506, or the Reo M35. Still, silicone fluid may be a good choice for HMVs that are not driven much – as long as you remember to check the level often.

Antifreeze also breaks down over time and is always being diluted by the addition of new water. Rust forms in the cooling systems of vehicles that are only trailered to shows, just as it forms in vehicles that are driven daily. Therefore, engine coolant should be drained once a year by opening or removing the radiator drain cock and all the drain cocks or plugs on the engine. Then, with the engine running, new water should be added to the radiator until all the water coming out through the radiator and engine block drains runs clear. Close all the drains and / or replace all the plugs. Finally, ill the cooling system filled with the proper mix of new antifreeze and water.

Many older HMVs that have not had their engines completely rebuilt in a shop where the engine block is “boiled,” may suffer from overheating problems due to lots of rust scale and debris in the engine water jacket. You are seldom able to flush this stuff out through the small drain plugs.

While there is really no substitute for “boiling” an engine bock, you might try removing all the soft (“freeze”) plugs and digging out as much scale and debris as possible. (Soft plugs are another item that should be checked occasionally for leakage or serious rust.) Likewise, old radiators often get clogged with scale and debris that simple flushing can’t remove. The only way to thoroughly clean an old radiator is to remove the tank and bottom (or the side tanks on cross-flow types) and “rod-out” the tubes. But, unless you’re very skilled in the art of soldering, this is best done by a professional.

Unfortunately, you may find that taking an old radiator to many modern radiator shops often results in your being sold a new or rebuilt radiator core. So, always try to find a shop that specializes in vintage vehicle radiators.

If your vehicle has an expansion tank, be sure to check that it isn’t half full of sludge and rust scale. Radiator caps should be replaced about every five years, or when their gaskets begin to rot or become brittle. Keep both the cap gasket and the filler neck clean, or the gasket may not seal and hold pressure.

The cooling system of HMMWVs consists of a “cooling stack” composed of the power steering fluid cooler, the engine oil cooler, and the radiator. This should be checked at least once a year, and more often if the vehicle is used off-road. The coolers and radiator should cleaned with low pressure water or low pressure air. Just like all radiators and coolers, the fins should be kept straight and free of debris such as dead bugs, leaves and grass.

While there are many cooling system flush products on the shelves of auto parts stores, you will probably find that most are not very effective, and thus a waste of money. Many people have also learned to avoid any such products that require a “neutralizer” after flushing. If the product is strong enough to need neutralizing, it’s often strong enough to eat an old radiator. On the other hand, there are many modern “stop leak” products that work very well, and may literally hold an old radiator together until you have the money to have it re-cored.

Battery water evaporates, whether or not a vehicle is used, so the battery cells should be checked frequently, and at least once a week in hot, dry environments. You should add distilled water whenever possible, but any water is better than letting the cells get low. Once the plates of a wet cell battery are exposed to the air, they lose whatever percentage of power the exposed area produced. For example, if the plates in a battery cell are ten inches tall, and one inch of those plates is allowed to dry out, that cell will lose ten percent of its power. This is a permanent loss, and adding more water, or even electrolyte, will not restore it.

The useful life of vehicle batteries varies a lot. How long a battery will last is dependent upon many factors, including the quality of the battery to begin with, extreme heat or cold, and how a vehicle is used. Shock and vibration can shorten battery life, as well as hard-starting problems in which a battery is often run low. The latter can be compounded if the battery is not fully recharged. An example of this is a vehicle that sits most of the time, so it doesn’t start easily, and then is not driven very far.

The average life of most wet-cell vehicle batteries is three to five years. You may find that bargain batteries don’t last very long beyond their warranties, while more expensive batteries may outlast their warranties by several years.

As a general rule, you usually get what you pay for when it comes to vehicle batteries. Spending twenty dollars more for the biggest and best battery might save you money in the long run, since a top-quality battery may outlast two cheapies. A large, good-quality battery may also save you the price of a towing bill, jump-start service, or an off-road rescue by being strong enough to start your vehicle in extreme conditions...or if you simply forgot to turn off the lights.

Keep in mind that, while an old battery may still start a vehicle and appear be strong, it might not have enough reserve power for long periods of starter cranking. While there are ways to test batteries, you may find that most of these tests only give one a general idea of a battery’s condition.

If you have any doubts about a battery’s condition, and/or its warranty period has been exceeded, you should probably consider replacement if your vehicle is going on a long road trip or out into the bush. For 24-volt HMVs using two batteries, it’s usually best to replace both batteries at the same time. You may find that if you replace only one, both will probably need replacing sooner than if you’d replaced them both to begin with.

On the other hand, thousands of perfectly good batteries are replaced every year because they are thought to be the cause of hard-starting problems, when the actual cause is something as simple as loose or dirty terminal connections. Look at your battery clamps for fuzz or corrosion every time you open the hood, and make sure they’re tight by trying to move them by hand. If your battery(s) is located somewhere else on the vehicle, check it as often as you check under the hood.

Also, check battery cables for tightness where they connect to the starter, starter switch, solenoid, engine bock, or vehicle frame. The negative, or ground cable, is just as important as the positive cable. If your vehicle has a ground cable or strap between the engine and frame, also check that for tightness.

Many vehicle components age and become unsafe or unreliable regardless of actual mileage or engine hours. Common examples are wiring (especially the Hypalon wiring of most vintage M-series vehicles), radiator and heater hoses, and fan and accessory drive belts. Things like these should be examined frequently.

The key word is “frequently,” but not necessarily on a schedule that one might mark on a calendar... though that’s not a bad idea. You should simply get into the habit of checking a few things every time you’re in or around your vehicle.

For example, when you open the hood to check the water and oil before a Saturday drive, take a few minutes more to check the condition and tension of the fan and accessory drive belts. Examine the belts for cracks, fraying, or glazing on their inner surfaces. The latter usually indicates that a belt has been slipping.

The most common cause of drive belt slippage is a belt being loose. Other more serious causes can be a generator, alternator, air compressor, water pump or other accessory with bearings that are becoming stiff and about to seize up. This can be checked by removing the drive belt and turning the accessory by hand.

A generator, alternator, water pump, power steering pump, air compressor, or any other accessory with stiff bearings should be rebuilt or replaced immediately. There is no way to judge when it may fail. Likewise, rebuild or replace any such accessory that has bearings that squeak or feel rough.

A badly glazed drive belt will almost always slip, and therefore should be replaced. Drive pulleys may also become glazed because of a slipping belt. If so, then sandpaper can be used to roughen them slightly for a better grip. Over-tightening a drive belt to compensate for slippage caused by glazing puts a lot of strain on accessory bearings, which makes them wear out faster. There are various “dressings” that may help keep a drive belt from slipping, but they are only a temporary fix: the belt should always be replaced as soon as possible. Another thing to look for is lots of black dust on the front of the engine. This usually indicates that a drive belt is wearing out because of a loose or misaligned accessory. This is especially common on vintage HMVs that have had their original generators replaced with alternators; and is something to check when buying a vehicle.

Also while under the hood, squeeze the radiator and heater hoses to see if they’re getting hard and brittle or developing cracks. On the other hand, a radiator or heater hose that feels soft and squishy may also be ready to fail because it’s decomposing. Old heater hoses usually break at their connections. When replacing such hoses, always leave a little extra length. Then, if the hose breaks years later out on the road, you will have enough extra to get going again.

Most hose clamps loosen over time due to expansion and contraction caused by heating and cooling, as well as vibration, and should be checked occasionally. Over-tightening hose clamps can cause a hose to break.

Sometimes, a radiator hose leaks, not because it’s too loose, but rather because a water inlet or outlet is rusty and rough, or badly pitted and corroded. Cleaning and smoothing a rust-scaled fitting with a wire brush, or replacing a badly corroded fitting, is better than over-tightening its hose. Gasket sealer is another alternative to over-tightening a hose on a badly corroded fitting.

Hose clamps should be installed about a quarter to a half an inch from the end of a hose, not at the very end. Position the clamp so its tightening mechanism is easy to reach, even if that may not be the “correct” position shown in a manual. Remember that most manual pictures and illustrations were made under factory conditions when a vehicle was new and untested in actual use. Also, many connections and fittings were positioned for fast assembly rather than for easy service in the field. (PS Magazine lists many field modifications that advise moving something to a different position.) All of the above applies to rubber fuel and vacuum hoses, as well.

Eyeball your engine for potential problems and failures-in-progress, such as ignition wires, heater hoses, fuel or oil lines, fraying against something. Pay special attention to wires or hoses near exhaust manifolds. The wire or hose might look fine everywhere else, but may be stiff, brittle or charred within an inch or so of an exhaust manifold or exhaust pipe. The same applies to areas under the vehicle. When replacing such items, try to route them as far as possible from heat sources. Keeping fuel lines away from heat sources can also prevent vapor-lock.

In regard to the ignition system, get into the habit of checking the distributor point and spark plug gap once in a while: also the condition of the spark plugs, even if your vehicle is starting and running all right.

Gear oil ages, breaks down, loses its lubricating qualities over time, and is another example of something that should be drained, flushed, and renewed about every two or three years. Although pricey, synthetic gear oil generally lubricates better and lasts longer than conventional oil. Like a top-quality battery, synthetic gear oil may be worth the extra money if you plan on keeping your HMV for many years.

Engine oil doesn’t only break down and become dirty from use, it also gradually breaks down over time. And, in vehicles that aren’t driven much, or are not driven long distances so the engine never fully heats up, moisture forms in the crankcase. Moisture also forms in engines, axles and gearboxes simply because of temperature changes. Water not only dilutes engine oil, it also reacts with the oil to form acids that soften and eat away bearing material. Therefore, you should change the engine oil at fairly regular intervals whether or not the vehicle is driven a lot.

Don’t forget the oil bath air cleaner, which should be serviced whenever the engine oil is changed, as well as checked and serviced more often if the vehicle is driven. The same applies to dry type air cleaners. Both oil bath and dry type air cleaners may need service on a daily basis if the vehicle is used off-road in dusty environments.

Components such as tie-rod ends and ball joints, steering knuckles, spring shackles, and universal joints obviously need to be frequently greased on vehicles that an driven; and even more often if a vehicle is used off-road. During use, grease is gradually worked out of components and bearings, as well as being contaminated by dust, dirt, mud, water and slush. But, grease also ages, breaks down and dries out on vehicles that sit most of the time. So, greasing all the vehicle’s fittings should be a fairly regular duty.

Just like changing the engine oil, the oil filter, and servicing the air cleaner, good lubrication is one of the cheapest forms of insurance against a vehicle breaking down. Most things break because of wear, and clean, good quality lubricants replaced often and maintained at their proper levels, considerably slows the wearing process.

Just because your HMV is “old,” there’s no reason why it shouldn’t be fully mission-capable Keeping your HMV “MC” includes servicing and replacing mundane items like windshield wiper blades. The place to discover they’re hard or rotten and won’t clear the glass is at home, not during a rainstorm out on the road.

Another item often neglected in HMV maintenance is the speedometer drive cable. For vehicles in fairly regular use, the drive cable should be cleaned (inside and out) about every two or three years, and assembled with either light grease or a graphite lubricant. Don’t use heavy grease: this can cause an erratic or “jumpy” speedometer, especially during cold weather. It’s usually best to not grease the last six inches of the cable at the speedometer end because the grease may work its way into the speedometer mechanism. The same applies to the service of mechanical tachometers.

Just as important as doing these simple checks, catching problems before they happen, and fixing things before they break, is having a few basic tools on hand. Every smart HMV owner has a basic tool set aboard their vehicle.

For those new to the HMV hobby and acquiring their first vehicle, you will probably find the following list of tools to be the most useful for doing roadside repairs and home maintenance on everything from WWII Jeeps, M151 MUTTS, M37s, M715s, M561s, on up to CCKWS, DUKWS, M35 and M211 trucks, and HMMWVs.

1. Set of combination wrenches, 5/16” to 13/16”.

2. 3/8” drive socket set, 3/8” to 13/16”, including a spark plug
socket. (Make sure the latter fits your waterproof plugs.)

3. 3/8” ratchet wrench.

4. 3/8” breaker-bar.

5. 3/8” socket extension 3-4” long.

6. 3/8” socket extension 6-8” long.

7. Pair of slip-joint pliers.

8. Pair of Channel-Lock type pliers.

9. Pair of wire-cutters or lineman’s pliers.

10. Pair of Vise-Grips.

11. 8” Crescent wrench.

12. 10-12” Crescent wrench.

13. Pipe wrench that opens farther than your
largest Crescent wrench.

14. Three or four good screwdrivers, including a Phillips-head.
(A good “four-in-one” screwdriver is also quite handy.)

15. Medium-sized ball-peen hammer.

16. Feeler gauge for setting spark plugs and ignition points.

17. Ignition points file (and/or some emery cloth).

18. Pair of very small Channel-Lock pliers for working on
things like the distributor.

19. Small chisel.

20. Probe type electrical tester..one that’s right for your
vehicle’s voltage.

For vehicles in daily use and/or vehicles that travel off-road, here are a few other repair, emergency, and troubleshooting items that may come in handy:

21. Roll of electrical tape.

22. Roll of duct tape.

23. Roll of baling (“mechanic’s”) wire.

24. Roll of 14- or 12-gauge electrical wire.

25. About six feet of 5/16” or 3/8’’ rubber fuel hose, plus a few
mini clamps. You can make emergency hose clamps from
your bailing wire or nylon cable ties ... another handy multi-
use item.

You should make up a pair of test leads about six feet long from 14-gauge electrical wire with alligator clips on each end, and preferably of different colors. Besides testing purposes, these can be used as emergency jumpers to bypass damaged wiring or to hot-wire your engine if necessary. Naturally, you should always carry a good set of battery jumper cables and a fire extinguisher.

An air compressor can come in handy. Those inexpensive electric models will work on 24-volt systems if you take a lead off the “first” battery. If your vehicle has an air brake compressor, rig up a hose with an air chuck...a hose long enough to reach all your tires. And, always carry a tire pressure gauge, a valve core tool, and a few extra valve cores and caps.

You should have at least one good-quality flashlight with an extra bulb; and for a trip into the bush, extra batteries would be wise. If your vehicle is not equipped with a sound system, carry a cheap little radio, along with extra batteries for it. In addition to keeping up with current events while out in the wilds, a radio can help pass the time if you’re stranded somewhere or making repairs. Of course, if you own a wireless phone, you probably take that wherever you go.

You should carry at least three road flares. Breakdown triangles like those required on heavy trucks are a good safety item if you have to work on your vehicle along a freeway at night. Without question, make sure you have a proper jack and lug wrench... and know, for a fact, they will work.

By now, it should be obvious that vehicles that sit for long periods need regular inspection and maintenance just as much as daily-drivers, though often for different reasons. All of a vehicle’s moving parts, whether in the engine, transmission and axles, wheel bearings, steering or brake systems, are constantly being polished during use and kept clean and free by their various lubricants. When a vehicle is sitting, oil drains away from piston rings, rocker arms, timing chains and transmission gears.

To recap one important point: most engines, gearboxes, fuel and air, tanks contain some moisture caused by normal condensation. This moisture builds up over months or years of seasons and temperature changes, and contributes to internal rust. This moisture also breaks down and reacts with engine and gear oil to form acids that eat away at metal and bearing material.

In addition, ferrous metal rusts, while copper wiring and brass electrical contacts in voltage regulators, terminals and switches oxidize and corrode. Fuel, whether gasoline or diesel, loses its volatile hydrocarbons and goes “flat,” forming varnish and sludge in fuel tanks, lines, pumps. and carburetors. Another hazard to vehicles that sit is the insulation on their wiring can be gnawed or eaten by rats, mice and insects.

Dust settles into everything that has even the smallest opening to the air. Of course, this also happens to a vehicle in normal use, but in use this dust is constantly being shaken out of electrical contacts and small moving parts. The grease in universal joints, wheel bearings, drive shaft slip-joints, and steering and suspension systems breaks down and dries out, leaving these parts to stiffen up and rust, often making the vehicle unpleasant or cranky to drive. Brake fluid, as we know, goes bad over time, besides the fact that it attracts moisture, forming gum and sludge in master and wheel cylinders, brake lines and hoses.

Rubber parts dry out, shrink and crack, in everything from weather stripping on doors and windows, to the internal parts of vacuum and air-powered windshield wipers. Tires contain a certain amount of oil that is continually being brought to the surface while rolling and flexing.

When sitting, tires dry out and rot, and may become unsafe even if they still look good. Tires may also develop flat spots on the bottom, which may not roll out when the vehicle is driven. The Bakelite, hard rubber, and plastic of steering wheels and shift knobs dries out, shrinks and cracks without the constant touch of human hands Products such as “Armor-All” seem to work well in protecting these things.

Humid climates are extremely hard on vehicles that are not driven much. This is mostly due to temperature changes that promote condensation in fuel and air tanks, transmissions and axles, so all of these things should be checked, serviced, or repaired or replaced at regular intervals no matter how little the vehicle is used.

How “regular” is regular? It’s really up to your own common sense, based upon your vehicle’s use and the environment in which it is used.

Common sense is one of the most important factors of HMV maintenance. You simply apply common sense in caring for your own vehicle in your own situation. It is often just a matter of realizing that it’s been five years since you replaced the radiator hoses or changed the gear oil.

In other words, it’s not always necessary to replace something just because “the book” says it’s time. Rather, use your own eyes and experience to determine if something actually needs replacement.

Common sense balances “fix it before it breaks” against “if it ain’t broke, don’t fix it.” If you need any more advice about basic HMV maintenance, here it is:

“It’s better to be safe than sorry.”

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