Know your vehicle, assuming the worst, hot tanking blocks, speedometers and more in this installment of ‘Tech Tips’

Good HMV maintenance is a matter of getting to know your particular vehicle. This process should start as soon as you get your vehicle home. Control that adolescent urge to drive the vehicle right away and show it off to your friends like a teen with his or her first car. I once bought an M38Al jeep that seemed to be in very good condition and ready to drive, but 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: safe rule of thumb is to always assume the worst with a newly acquired MV, no matter what the seller told you. 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, the rubber lines for cuts, cracks or simple old-age. If the 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 of the 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, which 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.

Many older MVs 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. One is seldom able to flush this stuff out through the small drain plugs. While there is really no substitute for boiling an engine bock, I’ve had good success by removing all the soft (“freeze”) plugs and digging out as much scale and debris as possible, then flushing the block with a hose.

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, I don’t recommend trying this. Unfortunately, I have also found that taking an old radiator to many modern radiator shops often results in being sold a new or rebuilt radiator core. 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 gasket and the 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 should be checked at least once a year, and more often if a Hummer 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.

Gear oil ages, breaks down, loses its lubricating qualities over time, and 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. 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, one should change the engine oil at fairly regular intervals whether or not the vehicle is driven a lot.

An 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 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. All the above also applies to the service of mechanical tachometers.

A: Most OEM tanks were terne-plated (an alloy of tin and lead) inside to prevent rust, but that may not be the case with modern replacements. If the inside of your tank is only lightly surface rusted, it’s probably OK to go ahead and use it. You might want to flush it first with some gasoline, and watch your fuel filter for rust residue. There are several products you could use to neutralize the rust: one of these is “Ospho,” which has been around since the 1940s and is fairly cheap. There are also coatings for the insides of fuel tanks, but they are expensive.

Oil bath air cleaners 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 even need service on a daily basis if the vehicle is used off-road in dusty environments. 

Send your favorite Tech Tip or question to Steve Turchet at military@aimmedia.com

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