M1070 HET - anybody know how to get a more reasonable/useful final drive ratio ?

[466Navastar]

Looking at HETs and like except the 45mph / low mpg....looks like the transfer case is reduction unit in both high and low and axles have reduction that Im not really sure that I understand....

below are specs that I would like for someone knowledgable to comment on - Im wondering if a direct 1:1 high range / whatever low range - transfer case was substituted and something could be done to eliminate differential carrier reduction - a final drive of 4.63 would be golden for highway use

can anyone explain how differential carrier / planetary hub works and if they know how to accomplish what Im looking for at a reasonable budget ?


Transfer: Manufacturer: Oshkosh Truck Corporation, 55000
Type: Two Speed, Air Operated Front Axle Disconnect
Ratio: 9.85:1 and 2.464:1

Axles: Manufacturer: Rockwell SVI 5MR
Type: Driving, Planetary Hub Reduction, Double Cardan Joint Steering Axles, 30/70 Split
Inter-Axle Differential Interlock: Manual Control
Gear Ratios: Final - 7.36:1; Differential Carrier - 1.59:1; Planetary Hub - 4.63:1

 

[NDT]

I thought the transfer case was 1:1 in high range? If it were me, I would replace the direct top hole Allison with one with overdrive. That should get you into 55 mph. Fuel economy improvements are hopeless. The planetary axles are in the truck's DNA, no reasonable changes can be made there.

 

[Castle Bravo]

I'm not much help in terms of answering your question, but I think the 9.85:1 is actually 0.985:1 and the transfer case is a ever-so-slight overdrive transmission. 2.464:1 is low range.