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M931 Recovery Trip

VULCANGUNNER

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Clay Center, KS
It should be an adventure for sure.

Drove the trucks 90 miles out of RRAD when I picked them up & they ran great.

One had dead batteries, the other had the coolant drained. Both had the air dryer outlet fittings conveniently broken off. Used the emergency trailer line to connect the air dryer & wet tank.

Only thing I don't have is a jack. Guess I'll block her up & dig a hole under the tire like on a tank!
 

VULCANGUNNER

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Got the trucks in my back yard!

Drove down to TX on Friday, got there about 10pm. Got up the next morning & jumped on the trucks at 7am. Checked all the fluids & fired them both up. Did an abbreviated PMCS on both trucks & found the following:

= Both truck's power steering pump return lines were jelly. (Replaced with weatherhead 400 psi 1/2" hose, $7.64 per foot at NAPA)
= One truck had listed in the maint. records that an axle seal was blown. Checked the diff & it was low (Filled, 2.5 gallons)
= Greased everything just in case
= Torqued all prop shaft flange bolts, found a few not tight.
= Replaced the hose & fittings that connects the air dryer to the wet tank with 1/2" hose barb fittings with 3/4" threads & the remaining expensive weatherhead 400 psi hose. (It was sabotaged at RRAD, see above)
= Topped off any low fluids (2 gal coolant & 1 gal of engine oil between the 2 trucks)
= Torqued all the hose clamps.
= Reinstalled the power steering box cover one one truck. (It was in the front seat with bolts & nuts in the holes, not even bent)
= Found very loose exhaust clamp at manifold to pipe connecton (help pipe up & torqued clamp, good to go)
= Figured out the exhaust pipe mount under the cab was rusted out & broken (Let it ride, clamp eliminated movement)
= Figured out the flasher module in one truck was dead. (Let it ride, ain't got a spare!)

Hit the road with both trucks running great. My 2nd driver is about 23 years old & has never driven anything bigger than an F150. I went through the operator's manual with him for a couple of hrs prior to the mission. He was still somewhat intimidated but he did a flawless job the entire trip & now he is an official 5-ton pilot! You learn a lot in 650 miles!

We stopped about 10 miles down the road to check transmission oil & air up all the tires (Goodyear road tires, all new). We got to checking tire pressures & all were quite low......so we spent the next TWO HOURS pumping air into Goodyears! I have one hose & we took turns airing up tires continuously for 2 hours!

So we hit the road & about 50 miles further my guy comes over the radio talking about he's losing power! He pulls over & I whip a gigantic u-turn in the middle of the road & go back. I get there the truck is idling but surging bad. He says it was floored but would only idle. Now these trucks have dual tanks & I was afraid to switch to the "other" tank because I figured they were probably full of crud. So I bleed the fuel line at the injector pump & I'm getting foamy fuel but no improvement in power. I did all I could think to do & it still idled like crap so we hit the road with me driving the goofy truck. We pull out & are climbing a hill & the truck is making power but not a whole lot. I top the hill & the power starts coming back on so I figure the fuel tank is pulling air. I said to **** with it & switched to the other tank. After about 10 seconds the power came right back on like a switch had been turned on! I was under the mistaken assumption that both tanks were almost full but it turns out my buddy who's house they were stored at had been firing them up every couple of months for like an hour each time. Very cool of him but I was short on fuel so we stopped & refueled outside Dallas & paid $3.37 per gallon.

We left at about 7pm, stopped for 2 hrs worth of air, 15 minutes of sucking air & foamy diesel, & drove until 3am. Stopped at a National Wildlife Refuge (LOL) & slept in the trucks. Froze my arse off, it was 39 deg that night. Hit the road again at 7am, drove all day until 10pm & parked them in my back yard.

We ran 55-60 mpg (GPS) all day long at 2050-2100 rpm getting right at 4 mpg the entire trip.

My truck's fan clutch was stuck ON & so I burned about 7 more gallons over the entire trip than the other truck.

We figured out that NHC-250's love to run at 2100-2150 rpm, they just seems to really "come on" right about there so that's where we ran them. I figured it was a cam profile / volumetric efficiency sweet spot.

The trucks performed admirably & I am now 100% sure I got a good deal. I have a bunch of little stuff to fix plus the axle seal but the trucks will run 650 miles so they can't be in very bad shape. Man those 931's will shake you plumb to death! Any other vehicle on the planet would have just fell apart from the shaking but we never lost a bolt. CARC paint on all those bolt threads is not necessarily a bad thing I guess.

Just before going to bed I went back out to where the trucks are parked side by side & actually thanked both trucks for not screwing me to death on the side of the road. I don't care what the neighbor thinks, these two 29 year old salvage Army trucks did me solid all the way down the line & I am very grateful for that.IMG_1796.jpgIMG_1800.jpgIMG_1801a.jpgIMG_1802a.jpgIMG_1806a.jpgIMG_1811a.jpgIMG_1812.jpgIMG_1832.jpg
 

Trailboss

Well-known member
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Location
Norwood LA
A fine looking pair! I was a little surprised at the low fuel mileage, but then I rarely go over 50 mph with my M818 with essentially the same engine. I haven't checked the other trucks yet.
 

VULCANGUNNER

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Location
Clay Center, KS
We were getting right a 4 mpg but the book said 3-4 mpg so I expected it.

We ran 55-60 mph all the way turning 2000-2100 cruising & 2150 just before a hill so she wouldn't bog. Hit the hill at 2150 & she'll hold 2100 at the top. Hit that same hill at 2000 & you'll be turning 1500 at the top!

Seems like my NHC-250's really start running about 2050 rpm & are rockin' at 2125 rpm!

My fan clutch was stuck engaged the whole time & my RPM readings are suspected to be 50 RPM lower than the truck with a free wheeling fan.

We haven't downloaded the flight data recorders yet. [thumbzup]

What do you get for mpg with your truck?
You have a M/T too correct?
I kept my automatic in 1-5 the whole trip & it never had to downshift on hills.
 
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VULCANGUNNER

New member
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Location
Clay Center, KS
My 931 weighs 22,100 pounds, 3600 pounds heavier than your 818.
The gearing is probably better with the 5 speed. What RPM are you turning at 50?
You have 6.44 ratio axles & I have 6.14 ratio if I remember correctly.

If the transmission gearing isn't dissimilar then theoretically your lighter, lower geared truck is under less engine load than mine at the same speed.

You are probably going 50 mph at the same RPM I'm going 55 or 60 mph so I'm burning more than you at given RPM.
 
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Trailboss

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Norwood LA
I usually get around 7mpg bobtail and 6mpg pulling a M871 trailer. I can do 50mph at around 2000, and that's what I try to travel at. I have some M931s, and a M923 but haven't had a chance to check the mileage since I refuel at the farm and can't measure the flow from my tank.
 

fuzzytoaster

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Where in Texas did yall pick up at? Also 4mpg sounds a tad low for a bob-tailing tractor. My smoking 818 got about 3.5mpg and the injection timing was way off, rolling coal all the way. I'd say scope that out when you can.
 
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