Checks for better battery PM.

Mechanics, doing PM on the batteries in your M939-series truck is a must! That PM is a lifesaver for the batteries. And since the batteries are in the truck cab, that PM can be a lifesaver for everyone in the truck, too.

Not doing good battery PM can lead to rusted-through cabs, leaving holes where they don't belong. You never want the batteries falling through the cab floor!

Check the Battery Blocks

Support blocks keep the batteries from bouncing around in the box and getting damaged. The blocks should go under the batteries and snug the batteries up against the retainer.

These blocks are shown as items 26, 27, and 28 in Fig. 153 of TM 9-2320-272-24P. Be sure to inspect these wooden blocks. Battery acid can rot them, and you won't want to use them like that. Replace rotted blocks.

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Check the Battery Box

Eyeball the box and cover during every scheduled service for cracks or corrosion. Replace any part that's unserviceable. The box is NSN 6160-01-093-5836, and the cover is NSN 6160-01-130-8045.

The cover seal, NSN 5330-01-104-7702, should be replaced if it's torn or so squashed out of shape that it doesn't form a good fit. Otherwise, fumes from the battery cells can leak into the truck cab. And fumes are no good for people.

Also, check the battery box vent drain hole. If it's clogged, vapors may not be able to vent. If the fumes have no place to go, this could cause breathing problems and/or an explosion hazard.

Remove any dirt or mud in the vent.

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Check for Corrosion

Keep an eye out for corrosion on the batteries and in the battery box. Most of the time, it starts when a battery is overfilled or a filler cap is missing. Electrolyte creeps out and turns into a gray-white powder when it dries.

This corrosion eats cables and brackets and gnaws holes in the box--unless you clean it first. So go after any corrosion you see with a solution of baking soda and water.

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Twice a Year

It's also a good idea to pull the batteries during semiannual services. That's the best way to find some of the hidden rusty spots and pinholes.

Those spots need to be sanded and painted. Holes need patching and patches need painting before the batteries are reinstalled.

Remember to check the vent holes after the box has been painted or patched to make sure they're clear.

Check the Batteries

Since the batteries are under the passenger seat and battery box cover, sparks fly if the cover gives way and the metal lid touches the battery posts. Rubber covers on the terminals keep the sparks from flying. Put 'em on like so:

Disconnect all cables--ground cable first--to avoid arcing the terminals. This is a good time to clean the clamps and battery posts with battery terminal cleaner, NSN 5120-01-430-1993.

Make sure the batteries are seated and clamped down.

Install treated felt washers, NSN 5970-01-101-4147, to prevent corrosion.

Install a rubber cover, NSN 2530-01-089-4992, on every post with a single cable terminal. Use cover, NSN 5940-00-738-6272, on terminals with one or more cables.

Push the terminal clamps all the way down on the battery posts and tighten them.

Lay the cable fiat against the battery before tightening the bolts.

Tighten the bolt and nut using two wrenches of the right size. (Never use an adjustable wrench.) Tighten the nut snug, then give I/a-turn more. Test by pressing and lifting the clamp with your thumb and forefinger. If it moves, tighten another 1/4 turn and check again.

Give the clamp and post a coat of silicone compound to prevent corrosion. The silicone runs down around the clamp and post to completely seal out moisture. Get a 1 -pint can with NSN 8040-01-331-7134 or a 3-oz tube with NSN 8040-01-331-7133.

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M1062 Fuel Tanker Spring

NSN 5360-01-528-3690 gets a heavy-duty 4-leaf axle spring for the 7,500-gal fuel tanker. You'll need U-bolt, NSN 5306-01-528-3676, to hold the spring in place. These NSNs replace the spring (Item 3) and U-bolt (item 5) shown in Fig 25 of TM 9-2320-384-14&P.