The Stovebolt Site Forums The Shop Area Driveline differential gear swap 3.73 to 3.07

well, I did some trading and got a rear axle out of a '71 chevy c10 to go in my '69 but was curious as to whether I will need to change the speedo gear in my tranny or will it be fine without this. thanks in advance,

Indy

Yes, speedometer gears will need changed.
Here is a gear list, http://www.transmissioncenter.net/speedometer_calibration_______va.htm
Here is a calculator,http://www.buickperformanceclub.com/speedo.htm

Basically, 3.07 is 82 1/2% of the 3.73, so you need to slow the speedometer down 18%. Look at the gears in the transmission, then look at the gears available.
Count the teeth on the driven gear, this is the larger gear that comes out the side of the transmission, then find a gear with 18% more teeth. The larger the gear, the slow it turns. If you can't get there with only the driven gear change, then you will need to pull the tail housing and change out the drive gear to a smaller one to slow down the driven gear.

Got that!

Joe