I have a 5 speed and a 4 speed auxiliary for my 1 ton, 20 gears. After doing the math it's more like 13 useable well spaced and without using overdrive with lower gears in the main per Spicer's recommendation.

•1951 GMC 250 in the Project Journals
•1948 Chevrolet 6400 - Detroit Diesel 4-53T - Roadranger 10 speed overdrive - 4 wheel disc brakes
•1952 Chevrolet 3800 pickup
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"First, get a clear notion of what you desire to accomplish, and then in all probability you will succeed in doing it..." -Henry Maudslay-