by Steve Turchet
My 1997 HMMWV is making a clunking sound when I stop. The sound seems to be coming from the wheels or underneath somewhere. - J. Peyton
HMMWVs are noted for brake problems which are often minor but annoying, such as shuddering, vibrating, squealing, or making odd sounds such as you describe. Check the bolts that hold the brake caliper brackets in place. Make sure they’re all tight. If loose, remove, clean, then reinstall them using a thread sealer such as Locktite. Also replace the lockwashers.
If loose caliper bolts weren’t the problem, check for worn out bushings on the suspension arms, which will also clunk. If these are in good shape, check the bolts on the half-shafts. These are prone to loosening and will cause major vibration and shuddering brakes, as well as destroying the oil seals.
Though supposedly waterproof, water may still get inside a HMMWV’s parking brake cables. (This can happen on just about any vehicle with this type of parking brake.) In very cold weather this water may freeze when the vehicle is parked, which may keep the parking brakes on even when the handle is released. If your HMMWV or other vehicle seems very sluggish when starting out in below-freezing weather, check for this problem. The only cure is to warm up the cables and melt the ice. Driving the vehicle this way can do serious damage to the brake pads or shoes and drums or rotors. And driving the vehicle will not thaw out frozen brake cables.
For those “extreme” folks who plan to deep-water ford their HMMWVs—which is an ordeal for any vehicle—you should be aware that the military advises stopping when the water is about 30 inches deep to let the vehicle fill with water. (Comforting thought for a ride that may have cost you well over $20k.) Otherwise, it may float away and capsize.
HMMWV PUMP PRIMER
Many HMMWVs, whether civilian-owned or in military service, don’t have the right fuel-injection pump installed, and/or the fuel-rate calibration is incorrect. This results in either over-fueling (which wastes fuel), produces black smoke, and is detrimental to proper engine lubrication, or under-fueling, resultsing in lack of power. Proper fuel delivery, either with the correct pump and/or the right calibration, is determined by the amount of equipment installed on the vehicle, and/or the type of variant.
Installing the correct pump with the proper calibration is especially important for HMMWV owners in the HMV hobby who often reconfigure a vehicle. Simply put, if you lighten a HMMWV fuel pump that was calibrated for heavy weight, you will be wasting fuel. On the other hand, if you add significant weight to a HMMWV without re-calibrating the pump, the vehicle’s performance may be degraded.
WATCH THOSE WASHERS!
If your HMMWV’s geared hub lockwashers are not bent properly into the locknut slots, the tabs may crack or break off. This increases the chances that the locknut will loosen, which could cause a wheel to fall off. Also, if the washer was installed incorrectly, the locking tabs may not seat fully in the slots. If so, the spindle lock nut may back off in the hub assembly and your HMMWV could lose a wheel.
EVERY WHICH WAY BUT LOOSE
HMMWVs are plagued by loose nuts, bolts, and components. One component prone to loosening is the starter. It’s hard to tell if a starter is coming loose just by looking at it. The best thing to do is get under the vehicle and push up on the starter. If it moves, it’s loose, so tighten it.
A loose alternator mount is another common occurrence. Like a loose starter, it’s hard to tell with a visual inspection. Grab the belt—top and bottom—push and pull, and watch for any movement of the alternator or bracket. If you see anything more than a tiny amount of movement, the mounting bolts are loose.
Vehicles that sit for long periods of time suffer many complaints. Besides the obvious—rancid fuel and fuel system problems, moisture in the crankcase, rust, corrosion anddeteriorating tires—sitting is also hard on brake systems, especially for vehicles with air or vacuum boosters. If you start and run your vehicle without actually driving it, get into the habit of stepping on the brake pedal a few times to keep everything free and working smoothly.
On vehicles with air systems, be sure to drain the air tanks after starting and running the engine. Related to this, there has always been controversy about the proper way to store a vehicle for long periods of time and best preserve its tires. Some people say it should be up on blocks with its tires just touching the ground, while others say the tires should be completely in the air, while still others advise that it’s best to leave the vehicle parked normally.
It’s been my experience that tires—especially bias types—will often develop permanent flat spots if a vehicle sits for months without moving; and tires will often rot where they contact the ground or a concrete floor. I see no logical reason why tires should not be completely free of the earth when a vehicle sits in storage. This should tend to keep them round because there’s no constant pressure on one specific spot.
This method has an added advantage, because the vehicle can be started and all its drive wheels engaged to keep axles, bearings, differentials, propeller shafts, transmissions and transfer cases free and well lubed without actually moving the vehicle. Of course, the blocks should be secure to keep the vehicle from falling off; and you’ll take precautions about the engine exhaust if the vehicle is inside a shed or garage.
Send your favorite Tech Tip or question to Steve Turchet, c/o Military Vehicles Magazine, 700 East State St., Iola, Wisconsin 54990-0001, USA, or e-mail firstname.lastname@example.org.