Originally Posted by 56trucknut
If I put in a 4 speed manual trans what rear end gears do I need?
A 4 speed will have a 1:1 final gear just like your 3 speed does, so it will essentially do nothing except make you shift another time. Thus, you will not gain any "speed" from a 4 speed (unless you are referring to the 3 speed with OD as a 4 speed).
I've talked to folks who installed a 3.08 rear and kept the 3 on the tree. They get decent highway speeds without the high RPMs. The extra speed comes with a tradeoff. With the 3.08 rear, you'll lose power in all gears compared to whatever you have now. You'll notice it most when starting off in 1st gear, especially on a hill. If you had an engine with more HP, then it'd be less noticeable.

Finding a suitable OD transmission and keeping the rear diff you have will give you the best solution IMO.

Last edited by Lugnutz; 07/30/2015 4:04 AM.
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