Old 6.2L GM military truck ... Talk me out of this......

Rmay635703 said:
His original setup many years ago (at this point decade +) was an automatic, some body/aero mods and changeable rear axle ratios so he could tow or highway cruise. From memory That airplane rear netted him 40mpg+ without any fancy driving.

If you have an overhead hoist, quick connects and pulse tools maybe it would be worth swapping the rear axle between hauling season and cruising season (from what I remember he towed a lot certain months of the year so the axle stayed put much of the time)
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It's a pretty cool idea, and low buck, if you can do the work. Almost like summer and winter tires. Instead of finding the best compromise... just go for the best in the situation. [Sorta--there was probably times when he had towing gears but wasn't towing, just like plenty of bare clean roads in winter time. Best most of the time.]
 
atikovi said:
Can it even do the speed limit? Engine probably redlines at 50 mph. Whenever I pass a convoy of military trucks, they are doing about 45, and even at that speed the engines seem to be screaming.
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the pictures suck, but i usually cruise at 55. interestingly, the speedometer works and is accurate, most of the time, sometimes it is 5 mph high..oil stays at a steady 40ish at speed, coolant temp is really low, like 140.....i think I need a winter bra.
 
burbguy82 said:
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the pictures suck, but i usually cruise at 55. interestingly, the speedometer works and is accurate, most of the time, sometimes it is 5 mph high..oil stays at a steady 40ish at speed, coolant temp is really low, like 140.....i think I need a winter bra.
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Although I have never followed t-case modifications it does appear that the np205 t-case has a 1.96-1 low and can accept a twin stick mod.

If you find that you NEVER use low range a swap to a 205 and a twin stick mod would allow you to more cheaply get a 4wd low range of 4.56 or more and an airplane gear range in 2wd only (being a little creative, but being a 2 range you loose the creeper gear in 4wd)

It looks like there are so called automatic and even 3 gear mods for various GM t-cases but all look rather involved and unknown on price.
 
Rmay635703 said:
Although I have never followed t-case modifications it does appear that the np205 t-case has a 1.96-1 low and can accept a twin stick mod.

If you find that you NEVER use low range a swap to a 205 and a twin stick mod would allow you to more cheaply get a 4wd low range of 4.56 or more and an airplane gear range in 2wd only (being a little creative, but being a 2 range you loose the creeper gear in 4wd)

It looks like there are so called automatic and even 3 gear mods for various GM t-cases but all look rather involved and unknown on price.
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thanks for the info. i will look into it.
 
4wheeldog said:
I would bet the thermostat has a fairly large bypass hole by design. So a radiator blocking strategy might be a good solution.
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it does have a hole, maybe less than an 1/8 inch. There is a winter canvas bra, that the military issued with the truck, for use in the winter to cover the radiator. i just put me a piece of foam which seems to help. thanks
 
Rmay635703 said:
His original setup many years ago (at this point decade +) was an automatic, some body/aero mods and changeable rear axle ratios so he could tow or highway cruise. From memory That airplane rear netted him 40mpg+ without any fancy driving.

If you have an overhead hoist, quick connects and pulse tools maybe it would be worth swapping the rear axle between hauling season and cruising season (from what I remember he towed a lot certain months of the year so the axle stayed put much of the time)

My 2wd 82 diesel suburban had a 2.8 rear and a 5 speed granny/ overdrive. Had to really slip the clutch with an 18ft enclosed trailer but most of the time I had the rear seats down, a trailer hitch support slung on the rear for the tent and flirted with 30mpg at 55mph. I had 15” tires, and the truck sat quite low compared to the ops setup.

The ops non-locking turbo 400 with big wheels likely has a MPG sweet spot with a very different rear end depending on his typical speed. Guessing 3.02-3.5ish depending on how much she slips.
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i am not sure of mpg just yet.
 
Interested to get educated thoughts on the Harmonic balance on the 6.2 DD. Internet says that the balance is an issue with these engines, and if they fail at speed.......the engine is or likely will be toast.

Is there any truth to this?

Fluiddampr...... https://leroydiesel.com/products/fluid-damper-for-ds4-or-db2/ seems to be a solid choice for this "issue", but I have to wonder with a factory style damper like from Napa......would I be getting one that has sit on the shelf for 30 years?

Not sure of the life of the damper.......any thoughts would be great.
 
burbguy82 said:
Interested to get educated thoughts on the Harmonic balance on the 6.2 DD. Internet says that the balance is an issue with these engines, and if they fail at speed.......the engine is or likely will be toast.

Is there any truth to this?

Fluiddampr...... https://leroydiesel.com/products/fluid-damper-for-ds4-or-db2/ seems to be a solid choice for this "issue", but I have to wonder with a factory style damper like from Napa......would I be getting one that has sit on the shelf for 30 years?

Not sure of the life of the damper.......any thoughts would be great.
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Yes breaks the crank
 
Rmay635703 said:
Yes breaks the crank
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I have seen that on many forums....but you know.....the internet and all its truths. Seems to be catastrophic, sometimes to more than just the crank.....some times destroys the block.

Ordered FluidDampr from Leroy, also got me severe duty clutch fan, and 7 blade fan as opposed to 5 blade. Will do all at once. I figure it will be a worth while investment.
 
burbguy82 said:
I have seen that on many forums....but you know.....the internet and all its truths. Seems to be catastrophic, sometimes to more than just the crank.....some times destroys the block.

Ordered FluidDampr from Leroy, also got me severe duty clutch fan, and 7 blade fan as opposed to 5 blade. Will do all at once. I figure it will be a worth while investment.
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I had an 89 Suburban that had the harmonic fall apart circa 2009,
It flew apart when I had it floored to pass going about 90.

Broke the crank but it still ran (hippity hoppity ) after that regardless.

If it were me I believe a unitized all metal harmonic is available, check to make sure yours isn’t hard rubber and replace it.

If you never hit high rpm it might survive but it only fails in the worse way at the worst time.
 
Rmay635703 said:
I had an 89 Suburban that had the harmonic fall apart circa 2009,
It flew apart when I had it floored to pass going about 90.
without fac
Broke the crank but it still ran (hippity hoppity ) after that regardless.

If it were me I believe a unitized all metal harmonic is available, check to make sure yours isn’t hard rubber and replace it.

If you never hit high rpm it might survive but it only fails in the worse way at the worst time.
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Yeah so at cruising speed, 50-55, in this truck, with 4.56 gears and 31 ish inch tires, without factoring in slip of the mighty TH400.....the rpm is on or about 2700-2800........I would consider it moderate speed.

I do floor it quite a bit. I think it is good for the engine.....and it is gutless.

I will upload pics if I remember.
 
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