1970 C3 Transmission date code P0A22A

[Roger S.]

I recently purchased a C3 1970 L46 and I am now documenting numbers. All went well with the engine and all numbers and dates match.However on the trans, the suffix on the date code is an "A" indicating the Muncie M20. But the window sticker shows the close ratio M21. Looking on the web I see the suffix for the M21 would be a "B". The correct vehicle VIN number is stamped on the transmission case so it appears to be original to the car.
Anyone have an idea on how I have a mismatch between the sticker and the stamp on the trans?

[Terry M.]

Re: 1970 C3 Transmission date code P0A22A

I recently purchased a C3 1970 L46 and I am now documenting numbers. All went well with the engine and all numbers and dates match.However on the trans, the suffix on the date code is an "A" indicating the Muncie M20. But the window sticker shows the close ratio M21. Looking on the web I see the suffix for the M21 would be a "B". The correct vehicle VIN number is stamped on the transmission case so it appears to be original to the car.
Anyone have an idea on how I have a mismatch between the sticker and the stamp on the trans?

I will offer two possibilities

A) The worker in Muncie Indiana stamped the wrong letter on the transmission as it was built

B1) The worker at St Louis pulled the wrong transmission from the stack.
B2) At St Louis there was a shortage of M21s and they put in what they had.

I guess that is three possibilities, but who knows. Remember they were just cars or transmissions going down an assembly line. The goal was to get them out the door and I doubt any of those workers ever thought we would be analyzing their product some 53 years on.

Opinions not asked for are often unwelcome, but I will go out on a limb and speculate that one of the B letters have the greatest possibility of occurring.

BTW: Mike E has an interesting story to tell relative to this, but it is his story to tell. I hope he sees this and chooses to share.

Have you had the transmission out and noted the two letter code ink stamped on the top of the gear box?

There are ways to determine the transmission ratios using accurate engine RPM and accurate MPH, but I will leave that mathematics wizardry to others who I am sure will be more help than I can be. Doing that would at least allow you to chose between A and B options.

[Patrick B.]

Re: 1970 C3 Transmission date code P0A22A

Another possibility is that the window sticker is a reproduction that it not accurate. What is the rear end ratio? If it is a 3.36, the M20 would have be the default transmission. Even with a 3.55, I believe it could go either way.

[Roger S.]

Re: 1970 C3 Transmission date code P0A22A

I think you are right. It looks like one can be built on window sticker.com that looks just like it. I was naive about the one I was given.
Thanks

[Roger S.]

Re: 1970 C3 Transmission date code P0A22A

Thanks Terry,
All logical possibilities but I'm now thinking the sticker is likely inaccurate.

[Terry M.]

Re: 1970 C3 Transmission date code P0A22A

Thanks Terry,
All logical possibilities but I'm now thinking the sticker is likely inaccurate.

Yep. That too.

[Mark F.]

Re: 1970 C3 Transmission date code P0A22A

I recently purchased a C3 1970 L46 and I am now documenting numbers. All went well with the engine and all numbers and dates match.However on the trans, the suffix on the date code is an "A" indicating the Muncie M20. But the window sticker shows the close ratio M21. Looking on the web I see the suffix for the M21 would be a "B". The correct vehicle VIN number is stamped on the transmission case so it appears to be original to the car. Anyone have an idea on how I have a mismatch between the sticker and the stamp on the trans?

Roger,
Do you have the Order Copy (aka Tank Sticker) ?
Unless the transmission option line was crossed out with a revision (initialed by a Plant rep) I'd think that would be most accurate at least for what the GM documentation system had for what was ORDERED (although maybe not installed, as others have said here)

[Bill B.]

Re: 1970 C3 Transmission date code P0A22A

Roger,

To determine which trans you actually have installed in the vehicle, I recommend doing the following:

On a limited access highway, cruising at a steady comfortable speed (i.e. 50 mph or so) in 4th gear, note the speedometer and tachometer rpm. Downshift to 3rd gear while maintaining the same indicated speed on the speedometer and note the tachometer rpm.

When you get home, divide the 3rd gear rpm by the 4th gear rpm.

If the result is close to 1.46, then you have the M20. If the result is closer to 1.27, then you have the M21 installed.