I found these documents and also took some notes, maybe it can help. I'm sorry if there are repetitions. The grail is at about 0.75 for the 5T truck. In some cases and I am not sure which, the OD ratio for the aux transmission depends on the -A, -B, etc. designation if any.- it looks like the 8031 is the best one to get for keeping RPMs down. The NHC250 is rated best at 1800-2100RPM
spicer 5831's FINAL RATIOS:
5831 "NO LETTER" 0.73, ALL SHOULD BE 580 FT-LB ACCORDING TO THE NUMBERING SYSTEM BUT THE WEBSITE SAYS:
Spicer 5831 Auxiliary Transmission Data
Length 18-13/23"
Torque 275 lbs. ft.
Horsepower 150
PTO 6 bolt-R/L
U-joint series 1410-1650
A 0.73
B 0.85
C 0.85
D 0.85
E 0.73
F 1.0
G 1.0
Spicer 6041 4-Speed Auxiliary 600 ft lbs 52MPH->60.5MPH
2.14:1
1.24:1
1.00:1
0.86:1
Spicer 7041 4-Speed Auxiliary 700 ft lbs 52MPH->62.6MPH
2.31:1
1.21:1
1.00:1
0.83:1
I think No.2Diesel said:
Spicer/Brown Lipe 8031C 3spd. Auxilliary. 800 ft lbs
Underdrive:--2.59:1
Direct:--------1.00:1
Overdrive:----.75:1
"Ok, here are some pics of the Spicer 8031C. Its an oldy but goodie. The Teeth & synchros look
great and the bearings have no wiggle. All it needs is a good wire wheel, paint and some gaskets.
They were nice enough to throw in a jackshaft and the original shifter. The shifter looks to be a
pretty simple affair.
Note the pic of the jackshafts next to each other. One is the original Mil. unit and the other came
with the Aux. box. The Civi. unit has .5" larger shaft diameter (3.25") than the 2.75" Mil. unit. The
Civi also has a larger section mudulus in the yoke department. Were not sure at this point to
change all the u-joints to the larger size. The flange on both Mil & Civi have the same bolt circle
and flange dia.
Maybe its better to snap a u-joint/driveshaft or two instead of blowing up gear boxes/t-cases etc.
We may just convert over as time goes on after the projects completed."