1967 L79 M20 rear end

[Gary H.]

I just got my car back from volunteering for the NCRS Judges Training Retreat in Grapevine, TX. Car's never been officially judged yet. One of the judge trainers (Pat. Should have noted last name.) said my differential might not be original or correct. I finally found a pic. I think I have a posi 3.70 June 29 1966. Can I get a second opinion? Thanks.

I'm a little confused by the single "6" to the right on the image.

[Timothy B.]

Re: 1967 L79 M20 reared

Gary,

What's the build date on the trim tag under the dash?

[Gary H.]

Re: 1967 L79 M20 reared

26 June, 1967

VIN: 194677S122643

[Edward J.]

Re: 1967 L79 M20 reared

Gary, you have the date correct June 29, 66, As far as being original to your car, its not likely, but as they say never say never, its date stamp make its likely for a very late 66 or a early 67.

[Leif A.]

Re: 1967 L79 M20 reared

And, didn't all L79 in 1967 come with M21 not M20??

[Timothy B.]

Re: 1967 L79 M20 reared

26 June, 1967

VIN: 194677S122643

Stamped K 26 ?

[Gary S.]

Re: 1967 L79 M20 reared

I thought the same, but not all 67 L79's had M21. It depended on the rearend it seems. My very original 67 L79 has a 3:36 rear and M20 and that is on the tank sticker too. I think if you have a 3:55 and lower you got an M21. And higher got you an M20. I am sure someone will correct if that is not right.

[Gary B.]

Re: 1967 L79 M20 reared

Gary, you have the date correct June 29, 66, As far as being original to your car, its not likely, but as they say never say never, its date stamp make its likely for a very late 66 or a early 67.

Edward,

Why do you say "not likely"? The C2 Registry birthday calculator lists an estimated birthday of July 7 for Gary's VIN. Yes, the rear diff date of June 29 is close, but perfectly possible.

Gary

[Gary S.]

Re: 1967 L79 M20 reared

Can you read the casting date on the side of the case? If cast in 67 it would seem you have a character missing in the assembly stamping is all.

[Richard M.]

Re: 1967 L79 M20 reared

I just got my car back from volunteering for the NCRS Judges Training Retreat in Grapevine, TX. Car's never been officially judged yet. One of the judge trainers (Pat. Should have noted last name.) said my differential might not be original or correct. I finally found a pic. I think I have a posi 3.70 June 29 1966. Can I get a second opinion? Thanks.

I'm a little confused by the single "6" to the right on the image.

Gary, When I zoom in on the diff photo I seem to see traces of a very lightly hit "7" after the 6, which would be "67". The year should be 2 digits. It looks like the diff was painted so it may be easier to see if you clean the paint away in that area.

Is your car body AO Smith built? K26?, as Timothy is hinting to? If so that may be why the build date on the Trim Tag is off from the estimated calendar build date, and 3 days earlier than the diff build date. June was the last month for AO Smith builds as all bodies in July were built in St Louis.

Also, the birthday calendar(estimated) shows your vin as July 7, 1967 build, so a June 29, 1967 differential seems legit to me.

Rich
PS Edit.... Gary Seymour ...... good idea to check the cast date

[Leif A.]

Re: 1967 L79 M20 reared

A picture of the housing in my June 14, 1967 built car for reference.

[Duke W.]

Re: 1967 L79 M20 reared

I thought the same, but not all 67 L79's had M21. It depended on the rearend it seems. My very original 67 L79 has a 3:36 rear and M20 and that is on the tank sticker too. I think if you have a 3:55 and lower you got an M21. And higher got you an M20. I am sure someone will correct if that is not right.

Only the close-ratio four-speed was available for the '65 L-79, and the standard axle ratio was 3.70. For '66-'68 you could also order L-79 with a wide-ratio four speed and the standard axle was 3.36.

Each trans also offered optional ratios. Details are in the AMA specs and NCRS Spec Guides that show all available drive train combinations for the various model years.

Duke

[James G.]

Re: 1967 L79 M20 reared

Gary, When I zoom in on the diff photo I seem to see traces of a very lightly hit "7" after the 6, which would be "67". The year should be 2 digits. It looks like the diff was painted so it may be easier to see if you clean the paint away in that area.

Is your car body AO Smith built? K26?, as Timothy is hinting to? If so that may be why the build date on the Trim Tag is off from the estimated calendar build date, and 3 days earlier than the diff build date. June was the last month for AO Smith builds as all bodies in July were built in St Louis.

Also, the birthday calendar(estimated) shows your vin as July 7, 1967 build, so a June 29, 1967 differential seems legit to me.

Rich
PS Edit.... Gary Seymour ...... good idea to check the cast date

I AGREE. And just maybe, the operator did not clock the stamp correctly.

[Joe R.]

Re: 1967 L79 M20 reared

Gary, Your rear end is just as original as any 67 produced by GM at St. Louis..

Parts were not sitting in a row by serial number or production waiting for the next car to come down the line.

Production workers crammed the first one they could get in their hands to keep production going and the checks coming.

JR

[Tim G.]

Re: 1967 L79 M20 reared

Gary, I think the "7" is either stamped lightly or just missing. Your tank sticker calls out a 3.7 rear end, so that further verifies that the rear end in your car is the original piece. If you have the warranty plate, the assembly date of your differential should match the date on the warranty plate.

Your car just keeps getting better and better. It was good to see you and your car at the judging retreat.