It depends on what ratios you have as to the difference in top speed.

Most have either a .85 or .73 overdrive, they help with top speed.

Some only have direct and two slower gears.

The 6066 link posted above has this info. And if you don't find what you need there I have a good bit of information on them, including the larger sizes.

Grigg


•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-