How can I find out if my transmission is original

[Jargo]

I have a 63 chevy c10 it has a Saginaw 3 spd transmission the number on it is
GM 31 3925647. Can anyone tell me when it was made?

[ray_mcavoy]

Hi Jargo,

I think what you found there is the GM casting number for the transmission case.

I Googled the 3925647 and it's showing up for a Saginaw 3-speed in the 68-72 year range. That'd be the one with the 7-bolt side cover and fully synchronized forward gears.

The earlier 3-speeds (like what your 63 would have had originally) have a 4-bolt side cover and a non-synchronized 1st gear.

There should be some additional numbers stamped (not raised up cast numbers) on a small flat spot just under the edge of the side cover. Should be a letter followed by a few numbers. The letter will tell you the assembly plant (most likely an S for a Saginaw 3-spd). The following numbers tell you the month and day it was assembled. But as far as I know, there's no partial VIN or anything on these transmissions that can be used to determine their exact original application.

[Jargo]

Thanks, I did not think it was original.