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The Hummer Knowledge Base

Driving a Humvee (HMMWV):

Here's some random advice from somebody who has experienced the pain and pleasure of owning a surplus HMMWV for a little over a year:

  1. Don't drive it over 55 MPH. You can get the truck to go 65+, but I'm told that going over 55 MPH over-revs the engine on a HMMWV with a non-overdrive transmission. Driving over 55 might have had something to do with my expensive blown head gaskets...

  2. If the engine hesitates to speed up or slow down when you change the accelerator pedal position, that's a fairly sure sign that the fuel injection pump has leaky seals, and will need to be replaced or rebuilt.

  3. Check the bolt that makes the ground connection from the current shunt in the battery box, through the transmission hump and to the gorund cables under the truck. On my truck, and at least one other collector's truck, the nuts were bottomed out on the shoulder where the threads end, causing a loose connection, arcing, intermittent electrical system failures, and a fire hazard. The solution was to take it all apart, replace the parts damaged by arcing, and add more washers to make sure the connection is tight without bottoming out the nut. Of course, don't forget to disconnect the ground connection at the battery before touching any other electrical parts!

  4. ALWAYS carry a fire extinguisher in the truck.

  5. Carry a pair of wheel chocks... the tranny doesn't have a park position, the original parking brake (the one what uses a separate disc on the driveshaft) isn't all that great, and there's no latch to keep the parking brake from being disengaged by bumping the lever. I chock a wheel when I park on a slope, and sometimes on flat ground, too. They'll be handy to have if you need to fix a flat, too.

  6. Disassemble, clean and properly lubricate the parking brake mechanism, and then adjust it as described in the tech manual. It makes a BIG difference. The knob at the end of the handle is only for minor adjustments to compensate for pad wear; there's another adjustment under the truck that has to be right for the brake to work properly.

  7. It seems that a lot of the trucks that went through Riverside had their neutral-start switches disabled by cutting the wires and twisting them together... sometimes on trucks with perfectly good switches! Check yours for proper operation. A friend's HMWMV almost got away from him when he started it from outside the truck without realizing that it was in gear!

  8. The lubricant packs on the runflats are often no good -- possibly because the trucks sat around long enough to lose a lot of air pressure, and then were rolled or driven around the auction house yard. I recommend dismounting each tire and inspecting its innards for runflat damage, and then either replacing the runflat lube packs or removing the runflats.

  9. Don't forget that the old 8-bolt rims must ONLY be used with the 36" BIAS PLY military tires. They have a burst limit of 30 PSI, and can separate under pressure (that is, EXPLODE) if used with radial tires.

  10. Check ALL of the fluids, flush the cooling system, and refill it with a proper antifreeze mixture. Fluids are commonly drained before military trucks are sent to the surplus yard, and the auction house refills them with whatever's convenient... Flush the cooling system by removing appropriate hoses and running water through various parts of the engine; just using one of those chemical flush products doesn't do a good enough job.

  11. If the two small hoses at the top of the coolant surge tank are plugged (like mine were), it makes it hard to add coolant, and it makes the symptoms of a blown head gasket really wierd! Mine were plugged up at the surge tank nipples. It's easy enough to check them, clean them, and even repalce them if necesary, when you're flushing the cooling system.

    Mark


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