Not your regular Bobbed 6x6

98G

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Can these transfer cases be swapped into the M39 series of 5 tons without too much difficulty? Assuming they are air shaft rather than sprag type?
They're air shift.

The ratios aren't the same. It really isn't worth mating up the Tcase out of the M939series with the transmission out of the M809series as you end up with a gear or two that aren't useful.

I'm thinking the M39 series is the same as the M809series except for the engine. Correct me if I'm wrong.

I'm guessing that your potential motivation to do so would be to ditch the sprag in favor of air shift. My opinion is that losing the robustness of the T138 to get the air shift of the T1138 isn't really an upgrade, even before you figure in final drive ratios. (I own both 939 and 809 trucks. I have no "mine is better" bias.)

Wandering off topic, my experience has been that the 809series trucks perform pretty well even without lockers. I got one stuck in soft mud and buried it to the axles. The sprag worked like it was supposed to, and it was spinning all 10 wheels. I did finally get it free under its own power.

A word or two on 16.00's. They noticeably rob bottom end power. To the point that it effects driveability. This is less of an issue in 809series trucks than in 939series trucks. It's like every gear is one gear higher than before.. I have 16.00s on my M925 and end up using the Allison auto like a manual transmission. Running around on back roads at 45mph i end up holding it in 4th gear and really only see 5th for the interstate or higher speed highways. If your truck actually works for a living you may want to consider 395's. 395's are considerably cheaper than 16.00s, and don't take nearly as much away from the bottom end. If you're planning on doing low speed and heavy, 395's are worth a look.
 

tobyS

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I'm not sure if the TC (1138) of the 818 can handle backing in low, but with 16.00 it will matter.

what do you mean? Why wouldnt a transfer case be able to do reverse?
Transfer case in the 939 series can break under load when in low range and reversing. There is a plaquard that makes the warning on the 939 dash. By conversation above, you will have the T138.

With the much larger diameter tires, the torque on each axle is increased significantly also, so getting stuck can turn into broken TC in 939 series, just "rocking". I'm still not clear if the T138 has the same problem as the T1138 ( will re-read above).

Myself...I would make a 4x4, with dif. locks on the rear and air lock differential on the front. Shed a rear axle, put on springs & shock(s) with air bags for heavy load. You could shorten your cargo to around a tractor at the same time and put a 105 bed on it. Below is my deuce with spring and bag FYI.
 

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Tow4

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The 939series 5ton trucks have a 10:1 reverse gear. In low range, this is enough torque to break the transfer cases. Thus you can't back up in low range reverse in those trucks.

Not an issue in the older trucks.
Just remove the washer on the transfer case shift rod that automatically engages the front drive and you won't have any problems using reverse. You can engage the front drive with the switch on the dash if needed.
 

gimpyrobb

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Yes Kenny, a 939 case can go in place of an older unit. We did this on Opcom's 818 that we installed a M109 box on. That was the discovery that the 939 Tcases had overdrive in high range.
 

98G

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Just remove the washer on the transfer case shift rod that automatically engages the front drive and you won't have any problems using reverse. You can engage the front drive with the switch on the dash if needed.
I like that mod because it gives you high and low 6x4 and high and low 6x6.

While it removes some of the bind on the t-case in low range by not forcing low to always be in 6wd , it doesn't resolve it completely and low range reverse still runs a risk of breaking the t case.
 

royalflush55

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It's not going to matter where you drive or if you are in 2WD 4x4 or 6x6, that pesky steering geometry is going to be an issue.....but only if you turn.

Let me add this though, GM didn't compensate for ackerman angles on the 73-87 trucks. They were the same for blazers at 106" WB all the way to 164.5" WB of the crew cab. Maybe it won't be as much of an issue as I thought.
I do know the short WB ones are a lot harder on U joints!
 

Recovry4x4

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Yeah, that's hotshotable. There are guys with the 4500 and 5500 truck towing up around 25,000. WO/W M52A2 is only 17840#
 

m715mike

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Your video makes reference to the advice given about pulling your new truck home with an 18 wheeler. I believe when that advice was given in your other thread, they were discussing flat towing the truck. Putting it on a trailer is a whole different ball game!

That was a cool video! Congrats on getting her home! And, I’m looking forward to watching your build!
 
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Flat towing, trailer towing, the guys on here were all but certain a regular truck couldn't do it. Honestly i was worried about the dude coming down the mountain with it. Either way, you guys probly saved my ass in more ways than one.
 
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I was talking to a bunch a people on a bunch of forums. It may not have been one of the steel soldiers guys. Either way there were a bunch of nay sayers. I thank the communities for all the input, it got here safely and nobody got hurt/tickets. I'll be happy to post pics of it when im done building it.
 
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