Springs

Hi Guys,
Just took the HMMWV out for my first 4 hour off road adventure on Friday. Let me start off by saying that this truck rocks off-road and I don't want to compromise what it is, I am keeping it completely milspec HMMWV, camo and all, that's why I bought the military version. Now, on to the issue, is there a spring that will soften up the ride a bit? The parts manual lists several but doesn't really discuss ride quality and I am not sure how to tell what mine are. I did some searching, but didn't have much luck there either. This truck rock crawls great but is harsh on the dirt washboard roads. I was running the tires at 30lbs witch may have been part of the issue. Should have dropped it to 20? Anyway, I attached a picture of my current rear springs.

might want to include which version of the truck you have to start with.
Ride quality has never been a consideration on these trucks for the military, only whether it will handle the load it's rated for, so if you want better quality of ride you might have to look at the civilian world. That being said, lowering tire pressure will probably help at least a little.

Sorry, 1990 M998 4 door soft top.

Hmmv4me said:

Sorry, 1990 M998 4 door soft top.

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The standard front spring in the front is 954Lb spring, it’s the softest they make...it’s in all m998’s.

Thanks. Any idea one the rears? That's what is in the image. I assume that mine carried a lot of weight at some point looking at the camber.

I believe all the M998 "A0" trucks had the softest springs (7700 GVW) unless you had a shelter carrier or prime mover that upped the spring rates?
As they moved forward, to the 10K and then 12K GVWs the springs just got heavier. Same with the shocks I believe.

Lowering your tire pressure will help the most. And a little weight in the rear wouldn't hurt...

What would you run at on the street vs dirt?

I run the pressures stenciled on the fenders for dirt F20 R25.
I dont air down off road unless I get bogged down

Ive been experimenting with 30 up front for street use.

I thought the old stencils saying 20 and 25 were for when they ran bias ply tires on the 8 bolt rims, the newer radials on 12 or 24 bolt rims should be higher than that. I've seen 30-45 in front and 35-50 for the rear depending on load.
The TM -10 says 20 front and 25 rear for the M998 at load for the radials, but it assumes that you will be doing a majority of off road hard surface driving at speeds of 30-40mph, not on road 50mph continuous. Reading through this forum and another one it looks like 40 or so is recommended by a lot of people for front and rear if you're primarily on pavement.

The only real issue I see with leaving them down in the 20s when running on pavement is the side walls will be flexing a whole lot at 50+mph, and that may lead to premature failure on them. The radials load range D are rated for 50psi cold, and if you get 24 bolt rims with the load range E tires it's 65 cold.

I have seen also that a memo was put out by the military (I just read that people saw it, I haven't seen it myself) that said to run all the radial tires at 45-50PSI, but that doesn't mean it will give a good ride, only that the tire has fewer failures at those pressures when the truck is loaded to full GVWR

DREDnot said:

I run the pressures stenciled on the fenders for dirt F20 R25.
I dont air down off road unless I get bogged down


Ive been experimenting with 30 up front for street use.

Click to expand...

I'll give it a try this coming weekend.

Thanks

The Operators Manual says 15psi is ok for off road. I’ve run as low as 10psi on mountain trails. No highway speeds for sure at that psi not above 30-35mph. I run 30psi on-road, 35 sometimes.
The ride will NEVER be gentle in a HMMWV
Bulldogger

Just came back from a Hmmwv trip...We ran 45 on highway [ 50+ miles ea. way on highway ] and 20 psi on dirt road...worked out nice.