Transission and rear end numbers.

[Jerry N.]

I believe I have the wrong transmission in a 1966 427/425hp car I just bought. It has S143976 on the drivers side which is not the correct vin#. 3831707 on the side cover, 3857584 GM on the tail, P0108 on the passenger side which I believe is Pontiac plant and the rest I don't know what it stands for. Rear end has 3871376 8 bolts, 7 leaf springs. I would appreciate anyone telling me the correct application for these parts. Also do all 427/425HP 1966 cars have transistorized ignition? I have ordered the NCRS books but they have not come so I used Chevrolet By The Numbers. Thanks

[William C.]

Re: Transission and rear end numbers.

The casting number on the pass side of the main case for a '66 muncie should end in 010. The P----designation is for the muncie transmission plant, but there is not a year code used in '66-67. the S-----VIN derivitive should match the one in your serial number which pretty well closes that you do not have the original trans, although it may be a correct case. I believe the 707 side cover was only used thru '65. yours should be a 685 casting for a '66

[Joe L.]

Re: Transission and rear end numbers.

Jerry-----

GM #3831707 transmission side cover is from 63-65 Muncie

Extention housing GM #3857584 is correct for late 1965 through 1970 Muncies

GM #3871375 is the differential COVER casting number; it is correct for 1966

7 leaf spring was used with cars with F-41 suspension which was available on L-72-optioned cars

All L-72 (425 hp) have transistor ignition

[Tom D.]

Re: Transission and rear end numbers.

Bill:

I believe they did use P7... for the model year 1967, but no P6 for 1966.

Or am I wrong? When did this start? Aug. 67 or later?

Thanks

Tom D.
4889

[William C.]

Re: Transission and rear end numbers.

You are correct, I was thinking of the ratio codes which were added in '69.

[Jerry N.]

Re: Transission and rear end numbers.

Thanks for all the help. I have ordered the NCRS books for 1966, but they have not come in yet. I used Chevrolet By The Numbers, and it appears that some of the data is incorrect. I would appreciate any help on what numbers to look at for the rear end and axle, and where they are located. The last 6 numbers of the vin are 118291, and if you know when the car was assembled I would appreciate it. Thanks again for all the help. Jerry Nutt

[Joe L.]

Re: Transission and rear end numbers.

Jerry-----

The manufacturing codes for the differential unit are stamped into the bottom of the case, just forward of where the cover attaches. They are often lightly stamped and you may need to clean the area with a wire brush to see them. Report what you find and we may ne able to decode. The VIN derivative is not stamped anywhere on the differential case so there's no way to tell, for sure, if any unit is absolutely original to a car. The manufacturing codes can only suggest if it's POSSIBLE that a particular unit is original to the car and "correct".

Your car was built ABOUT April 4, 1966.

[Jerry N.]

Re: Transission and rear end numbers.

The bottom numbers on the differential appear to be F A 3 29 66 The "9" is very hard to read and may be wrong. Thanks Jerry Nutt 31931

[Joe L.]

Re: Transission and rear end numbers.

Jerry-----

"FA" was the code for 1966-67 Corvettes with 3.70:1 rear gears and HD axles (427). 3-29-66 was the date of manufacture of the unit. It could be correct for your car as far as dates go (although a bit "tight", it would be considered to be an NCRS-correct date code for your car).

Just because the manufacturing code indicates that 3.70:1 gears were ORIGINALLY installed in the car, that does not mean that's what's in there now.