1969 M21 Transmission tag part number with 3:55 rear end L71 car

[Grant W.]

Hello all
Hope everyone is safe. Since March 15 I have been laid off, I have doing a lot of work on my 69 L71 engine. Putting on every nut and bolt that I have collected over the years.

Can someone tell me what is the correct transmission tag number for a
early built 1969
Assembly in Sept 68.
M21
3:55 rear end.
L71

Not sure if there is any tag number difference between a 68 and 69 M21 L71 car

I remember seeing a part number guide but I don't recall what book it was in? Its been 10 years and I forgot

My email is grantwong@telus.net

Thanks in advance for all your help,
Grant

[Joe L.]

Re: 1969 M21 Transmission tag part number with 3:55 rear end L71 car

Hello all
Hope everyone is safe. Since March 15 I have been laid off, I have doing a lot of work on my 69 L71 engine. Putting on every nut and bolt that I have collected over the years.

Can someone tell me what is the correct transmission tag number for a
early built 1969
Assembly in Sept 68.
M21
3:55 rear end.
L71

Not sure if there is any tag number difference between a 68 and 69 M21 L71 car

I remember seeing a part number guide but I don't recall what book it was in? Its been 10 years and I forgot

My email is grantwong@telus.net

Thanks in advance for all your help,
Grant

Grant------


I think it should be 3950316. However, since it's a very early 1969, it might have been 3915083. The latter was the 1968 transmission for the application but it's possible it carried over into early 1969.

[Chris H.]

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[Donald S.]

Re: 1969 M21 Transmission tag part number with 3:55 rear end L71 car

Grant, here’s the tag from my December 68 L71. [ATTACH=CONFIG]99998[/ATTACH]

That's the same number that's on my November 69 built L-71 M21 w/3.55
Don

[Grant W.]

Re: 1969 M21 Transmission tag part number with 3:55 rear end L71 car

Thank you all for your help. One step closer for the finishing touches on the M21 transmission
I appreciate it.
This info will help fellow restorers.

Thanks
Grant

[Joe L.]

Re: 1969 M21 Transmission tag part number with 3:55 rear end L71 car

All------


I was obviously incorrect on my conclusion that the transmission part number was 3950316. Here's what happened:

Unless there was some carry-over from 1968, there were only 2 M-21 transmissions used for 1969 regardless of engine option. These were GM #3946798 and GM #3950316. The only difference between them was the installed speedometer DRIVE gear. The 3946798 had DRIVE gear GM #3924097 installed. The 3950316 had DRIVE gear GM #3924098 installed. The 3924097 DRIVE gear was compatible with DRIVEN gears of tooth count 22 (green) to 25. The 3924098 DRIVE gear was compatible with DRIVEN gears of tooth count 18 to 22 (silver).

So, presumably, the GM #3946798 would be used with cars with M-21 and rear gear ratios of 3.70, 4.11, and 4.56 (with adapter) and the GM #3950316 would be used with cars with M-21 and rear gear ratios of 3.08, 3.36, and 3.55.

Unfortunately, I forgot that the 22 tooth silver DRIVEN gear, GM #3987922, did not exist until 1971. Therefore, 1969 Corvettes with M-21 and 3.55 rear gear ratio had to have used the 22 tooth GREEN DRIVEN gear. That means that 1969 Corvettes with M-21 and 3.55 rear gear had to have used transmission GM #3946798 and NOT the 3950316.

Adding to the confusion is the fact that GM originally cataloged the GM #3950316 transmission for "1969 with special hi-performance 427". That has to have been an error because the standard gear ratio for 1969 L-71 with M-21 (which absent otherwise specification of rear gear is what cataloged transmission applications are based on) was 3.55. No 1969 Corvette with L-71, M-21, and standard gear ratio of 3.55 could have used the 3950316 transmission. While I now know that's the case, the cataloged transmission application contributed to throwing me off when I made the my initial response.