gear change - Dodge Diesel - Diesel Truck Resource Forums

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gear change

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Old 10-13-2016, 09:27 PM   #1  
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Join Date: Nov 2009
Location: McCook, Nebraska
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gear change

I'm running an old FLD120 with a 400 N14, 10 direct, and 2.64 gears. It's just about due for an in-frame, with around a million miles.

If my math is right, a 13 speed with .78 OD and 3.36 gears would give me essentially, the same final drive ratio I have now. The same 13 speed with 3.23s would lower my cruise RPM from about 1500 to 1400 at 70 mph.

Would I see any appreciable gain in fuel mileage by swapping the transmission and gears? I'm getting about 5.25 right now, running 62-68 MPH, gross loaded weight 90K with a tri-axle trailer.
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