Discussion Forum - Northstar Chevelle Club

SShink · 3K+ Club

Muncie Trans ID Help

SShink · 3K+ Club

I also found 3952648 cast into the shifter opening cover and F1A66 stamped into the trans housing.

Bobs_Place · Vice President

The 3851325 case is 1964-65

The 3857584 tail shaft housing is 1966-70

And the J in the ser# is the plant code

Lost in the 60s · President

SShink wrote:
I also found 3952648 cast into the shifter opening cover and F1A66 stamped into the trans housing.

The F1A66 doesn't follow any coding I've come across. It should start with a P, the 1A should be 2 numbers indicating the month and the last 2 numbers indicating the day of the month but the 66 definitely isn't the 66th day of any month I'm familiar with...

The A in that code COULD, possibly, mean an M20 ratio, which most, if not all, the 1325 cases were built as.

The letter A is also used as a a January indicator.

The partial vin letter J would be for Janesville, WI assembly plant. They built full size cars, such as my '62 Impala SS.

And, yes, the 1325 case had a smaller diameter main shaft in the cluster gear than the models that came after.

hkgmillette · President

Here is a site I used to identify my tranny, www.rodauthority.com/tech-stories/drivetrain/identify-four-speed-transmissions/

jim larson · 2K+ Club

You may be able to determine whether its m20 or m21 by driving it hard and looking at your rpm, tire size, and rear gear ratio.

65 ratios 2.56,1.91,1.48, 1.00 for m20

m21 is 2.20, 1.64, 1.28, 1.00 Just drive it up to 5000 rpm in fist and 2nd. You should be able to calculate speed in 1st and 2nd at 5000 rpm.

I have to switch to reader glasses when under the car and looking at numbers 66 format is P for Muncie, one or two digits for month, and two digits for day, Mine is P1128 This format changed in 67.

That along with the Vin is stamped into the passenger side of the main case rear flange on the main case. Vin is also sometimes stamped into that flange on right side or scribed into the top of the main case.

584 tail started after 2/65

maincase 325 used through 65 model year.

Where is speedometer gear, drivers side for both, changed to passenger side in 66.