chevy to gmc tranny swap

[wc63]

my friend has a 283 chevy with a 3 on the tree he wants to make automatic. i have a 305 v6 gmc and want to keep it 3 on the tree but dont like the low gears on the highway. i max out at about 60mph. does anyone know if the 3 speed chevy tranny will work with the 305 v6 gmc. i was told if the bolt patterns match on the bell housing it will work, but i dont know if the gearing difference will affect my stock rearend. any help is appreciated. i dont know if it matters but both trucks are 1963.

[markeb01]

If both transmissions are 3 speed manual they should interchange just fine, but it won't help your freeway problem at all. Both 3 speeds are 1:1 (direct drive) in high gear.

There are essentially 2 options - change the rear end ratio to something higher (numerically lower) like 3.08-3.23. If yours is stock, it probably has something between a 3.73 - 3.90 in it now. The other option is swapping in something like a T5 with a .70 overdrive. A .70 overdrive will drop a 3.90 to something like 2.73, so a rear end change wouldn't be needed.