My first military vehicle

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New member
Thanks for adding me to the forum. I just wanted to post a pic of my 1992 M998 (6.2L and 3 speed) I purchased back in September. This forum helped me a lot to make sure I changed fluids and check various items. I spent hours researching many of your posts! Thanks!

One issue I think I'm having is a knocking or clicking sound while driving down the road, it's coming from the drive train since it changes with the speed. When I press the brakes a bit the sound disappears. I'm not sure if that's a sign that there is a problem with the drive shaft u-joints or something else. It's not something I'm particularly familiar with.

Some changes I made to my M998:
Changed wipers blades to Duralast conventional style blades
Replaced water pump with one from Rockauto - was previously leaking when bought it
Replaced belts with various attempts from Autozone and Rockauto parts - difficult find matched belts
Replaced hoses while changing out the water pump and pulled the entire rad stack
Replaced brake light pedal switch - intermittent issue with brake lights
Added a 12v transformer and wired up some USB and 12V power ports
Added an electronic rear-view mirror
Added radio tray with built in cup holders
Added Flightcom 4 person headset box and some headsets (Flightcom died within a couple of weeks during my first major offroading event, under warranty)
Replaced the dash light inserts from the green plastic to clear and put LED bulbs (major improvement)
RR Halfshaft started leaking grease from a crack in the rubber - replaced with GSP 10k lbs halfshaft instead of replacing boots

I'm looking for some ideas for new seats and how to set up the base of a new seat. I see lots of people switching to aftermarket seats but don't talk about the base and where the base comes from. I don't understand how the RF seat is so far to the left that half you butt cheek sits on a cushion.


Where have you found a good place to tie into for a 24v relay switch? Looking to add this as well to avoid draining the battery from the transformer I installed.

The other thing I'm looking at changing at some point are the tires. I haven't found a good source of the BFG tires. The goodyears on there now are very old, but no cracks.



Well-known member
San Jose, Ca
If you have a clicking sound that you think is coming from the driveline my advice would be to immediately stop driving it until you find the problem. You do not want a drive shaft or axle shaft coming loose on you at speed! The axles have a nasty habit of coming loose at the brake rotors. Crawl around on your creeper and look at all the bolts that fasten the axles to the rotors, make sure the middle driveshaft bearing is not in the process f disintegrating and all the other U-joints are solid.

There is a bolt at the wheel end of the half shafts (axles) that can also come loose. To get at that one you have to remove the wheel and a hole plug on the drop axle housing. This is also a good time to remove the side cover plates on the drop axles and check for water in the housings and bearing wear.

You didn't say which alternator you have installed but the best place to install a battery disconnect switch is on the negative side of the battery. In the battery box there is a large shunt assembly that's used to measure current to the starter and system that's a good place to install the switch. Don't scrimp here! Buy a good quality switch for this application, not some cheap Chinese knockoff.


New member
I'll check the bolts again at the brake rotors. Did this already when I purchased it but never hurts to check again. Something to add to my list next weekend.

I have the 60amp alternator. Haven't researched if that's something easy to upgrade. Good advice on the battery disconnect switch. Thanks.


Steel Soldiers Supporter
Alexandria VA
+1 on check all U joints and half shaft connections. The propellors (drive shafts) can also work fore and aft due to worn bushings/bearings, and that also could be it. Check the front propellor bearing too. It is bolted to the frame and provides lateral support for the reach from the transfer case. Mine was terribly worn. Easy to replace, relatively. And while that's off, good idea to do the U joints.
I had an annoying vibration that simply turned out to be an old reinforcement bar from a previous radio install that they didn't bother to fish out off the top of the transfer case, so maybe you'll find something like that and get lucky form having to investigate further.

For tires Eastern Military Surplus often sells pallets of 4 for a decent price, if you don't mind used tires (since they are Military Ozone rated they do have a longer service life than civvy tires). TreadWright sell remolded tires that seem to have a very good reputation. They are on my list when I buy tires next year. I don't see HMMWV tires on their site today, but they have had them in the past (perhaps and email to them will help).

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