HMV Maintenance

by Steve Turchet

Thousands of books and manuals have been written about operating, repairing, and maintaining virtually every make, model, and vintage of vehicle from the Model-T Ford to the newest SUV. In regard to historic military vehicles (HMVs), there are usually several manuals for each type and variant, from WWII jeeps to present-day HMMWVs. Regardless, there are some people who will pay thousands of dollars for a jeep, MUTT, M37, M35, or HMMWV, yet 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, keeping your 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, and fixing things before they break. These are few important lessons that you won’t “find in the manual.”

LESSON 1: TAKE YOUR TIME

Proper HMV maintenance is mostly a matter of getting to know your vehicle. This seems to be a new concept for many folks who’ve been raised to accept planned obsolescence. Too often, things are thrown away when they quit working simply because a newer model has come out, and/or it;s cheaper to buy something new than to fix something broken. This doesn’t work with HMVs!

Begin by making acquaintance with your vehicle as soon as you get it home. Ignore the adolescent urge to drive it right away to show off to your friends like a high-school sophomore with his or her first car.

Why? I once bought an M38 that seemed to be in very good condition. 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.

A wise philosophy is to always assume the worst with a newly-acquired vehicle. Assume that the gear oil in the transmission, transfer case, and axles is low, and/or dirty and worn out. Likewise, assume the same about the engine oil and power steering fluid.

Add to this, assume that the wheel bearings need repacking, the vehicle is overdue for a lube job, and the brake fluid is at least 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, and rubber lines for cuts, cracks and deterioration.

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 and condition of the engine, transmission and transfer case mounts. If a mount is deteriorated or broken, it should be replaced before driving the vehicle. Jack each wheel off the ground to check for loose or rough-running wheel bearings.

Most HMVs have drain plugs on their fuel tanks. On older vehicles, the plug may be rusted in place, so that will have to be dealt with. Then drain a little fuel into a glass container to check for water, which will always settle to the bottom.

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, grasp the fan and try to wiggle it to check for loose water pump bearings. Also check that the fan isn’t bent: a fan that wobbles will wear 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 the shoes may simply need adjustment. On vehicles with disk brakes, inspect each set of pads. On HMMWVs and CUCVs, it’s common for the brake assemblies to be badly corroded.

Make sure that all the vehicle’s lights, including the service stop lights and turn signals, are working.

Check every component 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 inspect all these things in a day, which should give you a good general idea of your vehicle’s overall condition. This inspection will also reveal how well — or not — the former owner cared for the vehicle, even if its last owner was Uncle Sam.

LESSON 2: SIMPLE MACHINE, SIMPLE ROUTINE

The concept that one size doesn’t fit all, and one book of rules, values, or standards doesn’t work for everyone also applies to servicing and maintaining most common collectible military vehicles. Unless your HMV 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.

Most common collector HMVs, such as jeeps, MUTTS, WCs, M37s, M715s, CCKWS, M211s, and M35s, are simple machines. They areeasy to work on with basic tools and shop equipment.

To some degree, the same can be said for the HMMWV. While a Humvee may seem very high-tech compared to a Willys MB, ninety percent of the machine is still just nuts and bolts.

There are some maintenance tasks that should be performed on every vehicle, no matter how much or how little they’re driven. Example of such tasks include changing the brake fluid, renewing the engine coolant, and checking the battery water levels. Likewise, all battery cables and terminal connections should be kept clean and tight. Check your battery’s water level at least once a month — weekly in hot environments — and keep it topped off with distilled water. However, ANY water is better than letting the level get low, so use tap water if you have to.

Don’t forget that battery grounds are connections too, and it’s just as important to keep them clean and tight.

LESSON 3: FLUSH BRAKES

Conventional brake fluid attracts moisture, whether a vehicle is driven or not. Therefore, the brake system should be drained, flushed, and the fluid renewed about every three years.

The simplest way to do this is to remove most of the old fluid from the master cylinder. A vacuum pump is handy for this task, but something like a turkey baster will work just as well.

Add new fluid, then bleed the system, either using the two-person method, or solo with a power bleeder or vacuum pump, adding new fluid to the master cylinder until the system has been completely flushed and refilled.

On most common HMVs, the process only takes about an hour. A “cheat” is to simply remove the old fluid from the master cylinder and add new fluid whenever the old fluid becomes dark or cloudy.

The question often arises as to whether one should use conventional brake fluid or silicone fluid. The main advantage of silicone brake 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 as much as conventional fluid. Silicone brake fluid is also more expensive than conventional types.

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, G.M.C. CCKW and DUKW, and Reo M35... though I have used silicone fluid in these vehicles without any problems. Silicone fluid seems ideal for HMVs that are not driven much… as long as you remember to check the level often.

LESSON 4: FLUSH YOUR ENGINE COOLANT

Antifreeze 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 about every two years by opening or removing the radiator drain cock and all the drain cocks or plugs on the engine. Then, with the engine running, add new water to the radiator until all the water coming out through the radiator and engine block drains runs clear. Close all of the drains or replace the plugs. Fill the cooling system with the proper mix of new antifreeze and water. You may also want to add additional anti-rust products, which usually contain a water pump seal lubricant.

Many older HMVs that have not had their engines rebuilt in a shop where the engine block is “boiled” may suffer from overheating problems. This is the result of lots of rust scale and debris in the engine water jacket. It is usually not possible to flush this stuff out through the drain plugs.

While there is really no substitute for boiling an engine bock, you can 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, older 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 better left to professionals at radiator shops. Always try to find a shop that specializes in vintage vehicle radiators.

If your vehicle has an expansion tank, 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 become hard and brittle. Keep both the gasket and the radiator filler neck clean, or the gasket may not seal and hold pressure.

The cooling system of most HMMWVs consists of a cooling stack composed of the power steering fluid cooler, the engine oil cooler, and the radiator. This assembly should be checked at least once a year, and more often if a Humvee 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, most are really not very effective, and thus a waste of money. It’s safer to avoid any such products that require a neutralizer after flushing.

Why? If they are strong enough to need neutralizing, they are 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 get it re-cored.

LESSON 5: CHECK BATTERY LEVEL

As previously mentioned, battery water evaporates whether or not a vehicle is used. Therefore, you should check the battery cells at least once a month — weekly in hot, dry environments. Again, 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. Adding more water 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. Extreme heat or cold, and how a vehicle is used will also impact the battery. Shock and vibration can shorten battery life, as can hard-starting problems during which a battery is often run low. This can be compounded if the battery is not fully recharged such as a vehicle that sits most of the time,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. Many cheap batteries don’t last 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 forgot to turn off the lights.

For HMVs with 24-volt electrical systems using two 12-volt batteries, always replace both batteries at the same time. Installing only one new battery will usually result in having to replace them both in the near future. Always pair the batteries as to type and size.

Keep in mind, that while an old battery may still start a vehicle and appear strong, it might not have enough reserve power for long periods of starter cranking.

While there are ways to test batteries, most of these tests only give a general idea of a battery’s condition. If you have any doubts about a battery’s condition and/or the 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.

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. In many cases, the actual cause is something as simple as loose or dirty terminal connections. Look at the 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 than in the engine compartment, 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 block 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, check it for tightness.

LESSON 6: MAKE FREQUENT INSPECTIONS

Many vehicle components age and become unsafe or unreliable regardless of mileage or engine hours. Common examples are wiring — especially the rubber-coated wiring of most vintage M-series vehicles — radiator and heater hoses, and fan and accessory drive belts. Items like these should be examined frequently. You should get into the habit of checking a few things every time you’re in or around your vehicle.

For instance, when you open the hood to check the water and oil, take a few more minutes more to inspect 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 the belt being loose. Other more serious causes can be a generator, alternator, air compressor or water pump with bearings that are becoming stiff and about to seize up. You can check these by removing the drive belt and turning the accessory by hand.

A badly glazed drive belt will almost always slip. Therefore, replace it (a temporary fix is to use sandpaper to remove the glaze). Drive pulleys may become glazed because of a slipping belt. If so, then sandpaper can also be used to roughen them 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 you should regard these as temporary fixes. You should always replace the belt as soon as possible.

Another thing to look for is lots of black dust on the front of the engine. This usually indicates a drive belt is wearing out because of a loose or misaligned accessory. This is common on vintage vehicles that have had their original generators replaced with alternators; and is something to check when buying a vehicle.

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 one of these may seize. Likewise, rebuild or replace any accessory that has bearings that squeak or feel rough.

LESSON 7: INSPECT YOUR HOSES

While under the hood, squeeze the radiator and heater hoses to see if they’re getting hard and brittle or developing cracks. A radiator or heater hose that feels excessively soft and squishy may also be ready to fail because it’s decomposing.

Heater hoses usually break at or near their connections. When replacing such hoses, leave a little extra length. Then, if the hose breaks out on the road years later, you will have enough extra to reattach and get going again.

Hose clamps tend to loosen over time due to expansion and contraction caused by heating and cooling. Check these occasionally with a screwdriver. Keep in mind, though, over-tightening hose clamps can cause a hose to break.

Sometimes, a radiator hose leaks, not because its clamp is 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. You can also use gasket sealer to seal a hose to a corroded fitting. This is just a temporary fix — the fitting should either be fixed or replaced as soon as possible.

Hose clamps should be installed about a quarter to a half an inch in 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. Most manual pictures and illustrations were made under factory conditions when a vehicle was new and untested in actual use. Many connections and fittings were positioned for fast assembly rather than easy service in the field.

PS Magazine contains many field modifications that advise moving something to a different position. All of the above also applies to rubber fuel and vacuum hoses.

LESSON 8: EYES ARE DIAGNOSTIC TOOLS, TOO

Eyeball the 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 and other heat sources.

While a wire or hose might look fine everywhere else, they may be stiff, brittle, or charred within an inch or so of an exhaust manifold or 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 every month or so. Check the condition of the spark plugs, too, even if the vehicle is starting and running all right.

LESSON 9: LUBRICANTS DETERIORATE

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 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.

Not only does engine oil become dirty from use, it also gradually breaks down over time. In addition, in vehicles that aren’t driven much or are not driven long distances so the engine fully heats up, moisture forms in the crankcase. Temperature changes will also cause moisture to form in engine crankcases, axles and gearboxes.

Not only does the water dilute the 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. This should be done at least once a year — even for show vehicles that may only accumulate a few hours of annual running time.

Don’t forget the oil bath air cleaner.You should service it whenever you change the engine oil. Check andservice it more often if you drive your vehicle in dusty environments. 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.

LESSON 10: KEEP IT GREASED

Components such as tie-rod ends and ball joints, steering knuckles, spring shackles, and universal joints need to be frequently greased on vehicles that are driven a lot — and even more often if the vehicle is used off-road. During use, grease is gradually worked out of components and bearings, as well as 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 of a vehicle’s fittings should be a fairly regular duty.

Just like changing the engine oil, oil filter, and servicing the air cleaner, grease is one of the cheapest forms of insurance against a vehicle breaking down. Most things break because of wear. If you replace lubricants with clean, good quality grease and maintain it at the proper levels, you will considerably slow the wearing process.

LESSON 11: MISSION CAPABLE

Keeping your HMV “mission capable” includes checking 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 in a rainstorm out on the road. Good maintenance for vacuum windshield wiper motors includes occasionally removingthe vacuum hose from the motor and spraying WD-40 into the motor while working it by hand.

Another item often neglected in vehicle maintenance is the speedometer drive cable. For vehicles in fairly regular use, the drive cable should be cleaned (inside and out) about every five years. Reassemble it using either light grease or a graphite lubricant. Disk brake grease is also usually suitable.

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. The grease may work its way into the speedometer mechanism. The same applies to the service of mechanical tachometers.

LESSON 12: TOOLS ON BOARD

Just as important as performing regular maintenance inspections, is catching problems before they happen. Fixing things before they break is the best practice, but when it isn’t possible, having basic tools at hand will help if you run into problems.

Every smart HMV owner keeps a basic tool set aboard their vehicle. This usually means a tool box that is stored in a locked compartment or under a seat. Being human, we may not want to go to the bother of digging out the toolbox every time we find a minor problem or something loose. Often, we decide to fix it later…and then may forget about it.

One solution might be to attach a carpenter’s leather tool pouch to the inside of a vehicle’s door or other convenient place in the cab. Equip the pouch with several screwdrivers of different types and sizes, a combination wrench set from 3/8 to 3/4 inches, a six-inch and a twelve-inch Crescent wrench, a pair of pliers, Channel-Locks, wire cutters, and Vise-Grips, a tire pressure gauge, a valve core tool, a feeler gauge, ignition points file, a little knife, a roll of electrical tape, and a small wire brush. Now, you have all the tools usually needed to tighten a hose or battery clamp, or a loose nut, bolt, screw, or connection, or to wrap a frayed something with electrical tape.

Most repairs and preventive maintenance can be done with the stuff in the pouch rather than digging out the main toolbox. If the engine isn’t idling right, snag a screwdriver from the pouch and adjust the carburetor in a minute.

There is no shame in not knowing what basic tools to carry in your vehicle. In many years of owning and driving various common collector military vehicles, I’ve found the following tools to be the most useful doing roadside repairs on everything from WWII jeeps, M151 MUTTS, M37s, M715s, M561s, on up to CCKWS, DUKWS, M35 and M211 trucks, and HMMWVs. Tools are like dollars: You can seldom have too many; but problems along the road of life are often compounded by having too few.

Here is a list of what should be part of a basic HMV tool box:

*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.

*3/8” ratchet wrench.

*3/8” breaker-bar.

*3/8” socket extension 3-4” long.

*3/8” socket extension 6-8” long.

*Pair of slip-joint pliers.

*Pair of Channel-Lock type pliers.

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

*Pair of Vise-Grips.

*8” Crescent wrench.

*10-12” Crescent wrench.

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

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

*Medium-sized ball-peen hammer.

*Feeler gauge for setting spark plugs and ignition points.

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

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

* Small chisel.

*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 I’ve found will come in handy:

*Roll of electrical tape.

*Roll of duct tape.

* Roll of baling (“mechanic’s”) wire.

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

*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 leads 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. Inexpensive electric models will work on 24-volt systems if you take a lead off the “first” battery. If your HMV has an air brake compressor, rig up a hose with an air chuck — with the 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.

You should always 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!

LESSON 1: TIME WILL TELL

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 repeat an important point: Most engines, gearboxes, fuel and air, tanks contain some moisture caused by 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 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 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 or 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 items.

Humid climes 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.

COMMON SENSE KEEPS ‘EM ROLLING

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. One simply applies common sense in caring for their own vehicle in their own situation. It’s often a matter of realizing that it’s been many 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. Instead, 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.”

One last tip regarding basic HMV maintenance:

It’s better to be safe than sorry.