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« on: March 12, 2022, 06:39:33 PM »
Semi trucks went through this along time ago.
It was found the lower numbered rearend gears were better for milage and engine life than overdrive transmissions.
Class 8 semi trucks started using overdrive auxiliary transmission way before my time. Probably the 1950's, than started using overdrive main box transmissions. Like
RTO-9513, 13 speed overdrive in the late 60's early 70's.
It takes more power to turn the overdrive gears with a higher number rearend gear than it does to drive a straight though direct drive trans with a lower rearend gear.
Before it was figured out there were 13, and 15 speed double overdrive transmissions.
When I was in high school my dad and I built a car out of junk parts.
A 352 , 2 barrel 4 speed out of a 1967 ford f250 truck.
The chassis was a 1979 LTD station wagon cut down and shortened up.
The wagon had a 2.26 to 1 gear ratio rearend. We used the granny gear 4 speed out of the truck.
It would go 35 MPH in low first gear.
It would get 23 miles to the gallon on the highway.