Cross Country in an M820

Looks like the seats in mine...

Good seating only goes so far. The energy still has to go somewhere. I suggest you try out the seats in it before contemplating replacement/upgrade.

The long wheelbase should help some. My experience has been that the taller tires also help some. I attribute this to more sidewall flex.

Thanks 98. I think I'll take that advice and give the stock seat a try first. I didn't know, but I guess they at least have a spring and dampener. Once it's in the NW, it'll be staying local for quite a long time. If it beats me up too bad heading South, I'll look into an air ride once I get it to Florida.

Do you have any recommendations for tire pressure on the 395/85's running empty? I'll be in warm to hot weather the whole time trying to run between 55-60 mph.

i like the spring seat in my deuce, not sure how much it likes 6'2" 325 me but after i lubed up the pivots and cranked up the preload on the spring i only bottom out on the nastiest horse graves in our lovely loserana roads, for a bit more room between me and wheel i am running a slip over padded cover on the rear hoop instead of a normal upholstered board like the lower, not sure of the original padding as mine was missing and the upper frame was bare.
air pressure on 395s, im sneaking up on it in my 109a3 at 30-35 in the rears and 35-40 in the fronts, basically you are looking for full tread contact as you will only be running on the center part of tread with too much air or not enough weight, couple concrete blocks might help the ride and allow the suspension to do more then bounce and slam

I am surprised no one mentioned desplined front hubs or removing the middle axle to free up the drive line on such a long drive.

Thanks Winfred. I'm only 140 lbs so I'm hoping the seat can be dialed down enough to not throw me against the roof. I'm optimistically hoping that it's an old design when the average soldier wasn't much heavier than me, so maybe I'm in it's "intended weight range". Thanks for the tire pressure input. They're new 395's so I'll be able to see any uneven wear pretty easily I hope. I'll try to stay a little on the soft side in the rears. I suppose front axle weight will be normal, but I'd like to go a little softer there too and keep on a eye on the temps.

Seph- I'll be on summer pavement the whole trip so one drive axle is enough. Any advice you can give me on the desplined hubs up front and what drive lines, axle shafts etc. to pull in the rear will be appreciated. I can do all that in FLA. I can do a little fab work but I won't have a lathe there to make "hub caps" or anything if I pull an axle shaft.

How well do desplined hubs work with the sprag transfer?

I think without weight they are more bouncy. My m818 beats you up hard unloaded, a 20 min ride is rough..Im trying to find an air seat. Anyway, bring a tire pressure gauge and a way to inflate tires (glad hand inflation works), but you will probably have to play with tire pressure. Too high and they bounce hard...to low and they bounce to much, Unloaded you're suspension might as well be 2x4s stuffed in there, there is little flex on those giant spring packs, so most of the suspension comes from the tires.

Thanks Wedge. I figured those spring packs wouldn't be moving a whole lot with almost no weight on them way back there. I'll try going as low as I can get away with and go from there. My cousin (the truck driver) runs to California about every week on I-10 and the joints beat em up, so he got the longest wheelbase he could and it really helps, he says. Used to hit both front axle and rear tandem at the same time, now it hits front/back, front/back and "rocks" instead. Anyway, time will tell I guess.

My impressions, spread out over a bunch of these trucks 939series, 809series and M44series....total of maybe 50,000 miles.

Regarding ride smoothness, they vary. Every truck is different. I drove an M931A2 from Indianapolis to Waco TX by way of Columbus OH. I didn't notice it being any better or any worse than the standard cargo variant.

I drove an M934A1 long wheelbase with the expansible box from Las Vegas to Phoenix. I didn't notice it being any smoother than the typical cargo truck.

I'm certain wheelbase has an effect. I just don't think it's in the top 3 or 4 variables.

10,000lbs in the bed has a pronounced effect. Comparison of the same truck empty or loaded heavy is a big difference.

Pulling another truck behind you on towbars makes a little bit of a difference but not much - there's not much weight transfer.

Big squishy tires make a big difference. Going from g177s to 16.00s on the same truck makes a big difference.

809series trucks tend to ride rougher than 939series trucks, everything else being about equal.

The tamest smoothest army 5ton doesn't approach the ride quality of the roughest civvy 1ton. Silverstate55 has a really nice m931A2 with air ride seats. It rides very smooth, even though it's a short wheelbase truck tractor. Lindsey97 has a standard length cargo truck with 16.00's on it and the standard seats. It drives as smooth as any I've driven.

My M818, with 16.00's and HEMTT rims is about the harshest riding 5ton I've driven. Still, it's not the end of the world. I've driven it on several trips longer than 1000miles duration.

I have had some decent rides in trucks with just cab&chassis, it's not for the faint of heart. The deuce was pretty abusive but the walking-beam suspension really helps, the 2-axle F-700 was practically suicide. If you are going to be doing mods anyway, I'd strongly consider desplining the fronts and buying an air-ride cutoff and mounting the new axles to the back. Otherwise, find the heaviest body you can bolt down.
Oh, right, also know that a cab and chassis truck can be dangerous if you brake hard. The rears lock up and then you are in real trouble.

I'm not wildly enthusiastic about the LED lights, too many failures and the cost is high. I went with halogen lamps in new reflector assemblies.

Hearing protection and intercom does really make those long trip easier to take. A few hours of loud truck is novel and cool, a few dozen hours is just tiring.

Thanks guys.

98, I appreciate the input from someone who's put some time in the saddle. I went with the taller tires for the "gearing" but it sounds like they might end up being my "suspension" too.

Teletech, between what you and 98 have said, it sounds like I might need to find something heavy to carry. Not just for the ride, but for safety. It'll be a little tricky with just frame rails, but I'll give that some thought too. I'm gonna try to avoid driving at night, but if I don't like the looks of the headlights (output wise) I'll probably take your advice and try some halogens before I go to leds. I like the led tail lights I have but I've never tried headlights.

You guys have me sold on some noise canceling headphones or earbuds. I figure I'll be on the road for a week on the cross country leg. I could get quite a few books on tape in.

Has anyone actually done desplined hubs on an M809series truck?

I think there's a show stopper....

I have a set on the front of my M813A1.

Sephirothq said:

I have a set on the front of my M813A1.

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The sprag doesn't go crazy trying to engage?

From what I can gather, it looks like you can install a valve and shutoff the air supply to the transfer case (by shutting it off before the main gearbox) and that will put a (working) sprag setup into a spring loaded neutral.

So it seems like desplined hubs and no air to the trans would leave the front axle just along for the ride, giving a little less drag.

I don't know enough to say whether or not this would create other wear problems. I don't want to take any unnecessary risks, but anyone that's done this and put in 10's of thousands of miles would know better than me.

hethead said:

From what I can gather, it looks like you can install a valve and shutoff the air supply to the transfer case (by shutting it off before the main gearbox) and that will put a (working) sprag setup into a spring loaded neutral.

So it seems like desplined hubs and no air to the trans would leave the front axle just along for the ride, giving a little less drag.

I don't know enough to say whether or not this would create other wear problems. I don't want to take any unnecessary risks, but anyone that's done this and put in 10's of thousands of miles would know better than me.

Click to expand...

Search 73m819's posts , he has posted quite a bit of information on sprags.

Thank you Porky. I will do that right now.

Just to streamline things for others (there's a lot of info AND confusion about 5 ton sprag clutches), yes, cutting off the air to the transfer case puts the sprag setup in neutral and combined with desplined hubs will give a "free wheeling" (not turning) front axle assembly. I'm considering getting the desplined hubs and I'm trying to get a better understanding of the sprag assembly now.

Thanks for the suggestion Seph. I never would have considered it otherwise.

Ducks are lining up in a neat row. I bought my plane tickets for me and my dad to fly into Philly on July 8th.

I confirmed with Eastern that the truck will be ready and on Monday, July 9th the adventure will begin. I'll post trip updates, lessons learned, etc.

I'm at sea now so not able to check this site much, but thought I'd update.

I just drove my M923A2 ROPS from St-Louis to Montreal (Canada) and the air seats are a must have for long rides

JC