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Tech Tips: Brake fluid, oil pressure, dim bulbs and more

Military Vehicles Magazine's Steve Turchet answers all of your HMV questions.
Tech tips Jeep

HMMWV Pressure

Q: What should hot oil pressure be on a HMMWV at idle?

Dave Morton

A: Most show about 30 psi at hot idle on the stock gauges.

Dark And Dirty

Most of us know that brake fluid becomes dark and dirty over time, and should be changed every two or three years by bleeding the old fluid out of the wheel cylinders and refilling the master cylinder with new fluid. Though most of us also know that conventional brake fluid is hygroscopic (meaning it absorbs moisture, which is the primary reason it should be renewed), do we ever wonder from where the dark and dirty residue originates? Mostly, it comes from the black rubber seals and cups in the master and wheel cylinders as they gradually wear from sliding back and forth. This is normal and unavoidable… unless we never use our vehicles’ brakes. The rubber parts of a brake system also deteriorate over time, and if you find your brake fluid becoming dark and dirty more rapidly and/or your vehicle’s master cylinder needs topping off more often, it may be time to replace or rebuild your master and wheel cylinders.

Staying Secure

I’ve received many letters over the years, usually from folks who have recently acquired an HMV, asking about or suggesting ways to make their vehicles secure from theft, since most stock HMVs don’t have key lock ignition switches. Some of the suggestions seem rather elaborate and complicated, so here’s my advice. While it’s generally true that if a professional thief wants a vehicle bad enough, and has the opportunity, they will usually get it. A steering wheel locking device such as “The Club” is one of simplest and most effective ways to keep someone from driving away with your jeep, Mutt, M37, M35, or HMMWV. Keep in mind that most chains and cable locks can be cut with bolt-cutters.

Dim Bulbs

Q: The instrument panel lights are very dim on my CCKW. It has the standard WWII instruments panel, not the early civilian kind. I have installed new 6-volt bulbs, but that didn’t help.

Rob Williams

A: The instrument panel lights ground through their housings to the dashboard. If the mounting hole and/or the lamp flange get rusty, this can cause dim lights. Likewise, if the lamp socket is corroded. Try cleaning the units with a wire bush or crocus cloth to see if that brightens things up.

Correct Clamp

If you’ve just finished brake maintenance, the last thing you want happening to your HMMWV is brake failure! But it can happen to HMMWVs with serial numbers 299,999 and below, if you don’t give them the special attention they need. Whenever you pull maintenance on any part of the brake system, make sure the loop clamp (NSN 5340-01-189-7640) that holds the brake line to the caliper on the right side of the vehicle is installed. If you don’t, you could be super-sorry! Your HMMWV’s brakes may not fail right away, but the jostling and rubbing could eventually lead to a long walk home.
 – PS Magazine

Don’t Unbolt!

You’ve got a lot of gear on while in full battle rattle. And that can be pretty uncomfortable when riding around in a HMMWV. Some soldiers have figured out that you can recline a HMMWV’s commander seat by removing bolts, resulting in a more comfortable ride. But what seems to be a good idea can really be a bad idea in disguise. Tampering with a HMMWV’s commander seat compromises safety. Without all the bolts, the seat will recline back all right, but it also could flop forward too far if you’re in an accident or if you have to stop quickly. That could get you hurt! Safety is more important than comfort. Keep all of the seat bolts in place. – PS Magazine


Having problems with suspension and steering components on older HMMWVs? You no longer need to order each and every part individually. TACOM and the PM for Light Tactical Vehicles developed a kit to improve the suspension and steering components, especially those with add-on armor. The new suspension and steering upgrade kit comes with NSN 2530-01-524-7319. The kit includes the pitman arm, idler arm, center link, upper and lower controls arms, ball joints, rear springs and shocks found on the M1097A2 vehicle for the rear of basic and A1 HMMWVs. This kit is estimated to take 14 hours to install, with frame welding required. HMMWVs in SWA will have the kit installed when they to go through the TWV Refurbishment Center, so see your DLA Customer Service Representative or TACOM LAR for more information before you order. One thing to keep in mind with this kit: It will not change the gross vehicle weight (GVW) or allowable payload of your vehicle. That would require several other configuration changes for performance and safety reasons. Kits are being procured and managed by DLA (S9C). Work continues on incorporating recommended changes to the kit (such as front springs, front shocks, tie rod assemblies, and radius rods), which will not only allow the kit to be used as an upgrade, but still makes it a great kit for the repair of suspension/steering components on a tired HMMWV. – PS Magazine

Is Two Too Many?

Q: I have an early model Ford GPW that I am restoring to D-Day landing configuration. I know that early WWII jeeps first came with hand-operated windshield wipers. Then they were issued with one vacuum wiper motor on the driver’s side and one hand-operated wiper on the passenger side. I have also seen old WWII pictures of jeeps with two vacuum wiper motors. Which configuration would be correct for a D-Day landing jeep? – Alan

A: By 1944, the most common windshield wiper configuration for jeeps in the European Theater was one vacuum motor for the driver and one hand-operated wiper on the passenger side. However, by that time, supply was catching up with demand in regard to wiper motor retro-fit kits, and many motor-pools, as well as jeep drivers, were installing two vacuum motors. Of course, by then, there were also many boneyard and damaged jeeps from which to salvage parts. It would therefore be safe to say that a D-Day landing jeep would probably have a least one vacuum wiper motor on the driver’s side, but would still be correct if it had two. 

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