[DANTIP]

I have a 1970 model year Service Replacement M21 (close-ratio) Transmission assembly and would like to know what it may be worth. I did find a reference to a GM service bulletin that documents how the Service Replacement Engine and Transmission assemblies are marked (see document below). My transmission is marked ?TO 38837, which according to the information below is correct for a full transmission assembly from the Muncie Transmission Plant. The case casting number is 3925661 and the date code is P0R29B (October 29, 1969, M21). This would be a perfect fit for a RAIII or RAIV car with the wrong transmission. The transmission is in my '66 GTO and drives/shifts perfectly.

[The Boss]

Actually, it's perfectly dated for a 68 RA I or II car.

[hobi]

How much do you want for it I have a customers 68 ram air II car its a automatic but he is thinking of converting to a 4 speed sounds perfect for him. That would make me happy as I would get a turbo 400 for one of my 69 convertible projects

[The Boss]

Hobi,

If you have a 68 PQ t-400 and want to trade it for a 69 PQ t-400 for your convertible, I'd do the trade with you. I also have a 68 dated M-21. Let me know. My e-mail is listed below.

thebosspontiac@hotmail.com

[hobi]

Thanks boss but I drove this customers car when it came in my shop it was really a nice shifting transmission I am going to just put it in my convertible as I know it works fine and dont care that its a 68 pq the circles I run in nobody knows or would care but thanks for the offer

[Judge273]

As I understand the way to decode a P0R29B tranny?

P = muncie,
0 is for year of car. 1970
R is month only 12 so not sure? But, say it is a replacement and fits all months. R does say Oct.
29 is day of month,
B is M 21?

[dr-doug]

Is it stamped for what it's replacing...when it's replacing...or when it was made?
Doug

[DANTIP]

Originally Posted by dr-doug

Is it stamped for what it's replacing...when it's replacing...or when it was made?
Doug

Interesting question. I would strongly suspect the manufacturing plant would have to keep a minimum amount of service replacements on hand. The plant would probably run them on an as needed basis to keep that minimum safety stock level. The Date code looks the same as the production units but the service/serial number is much smaller and very precise looking (like a machine did it). With all that said, I suspect the service replacements were marked relative to their production rather than for the vehicle they were destined for. Lastly, according to the documentation on the Service Replacements, there should be a character before the "T0" (like "PT0" for Pontiac) and it is either not there or it's too faint to see (the "T0" is really evident). My thinking there is this transmission would be able to replace any GM M21 (unlike a replacement engine). Therefore, the first character was probably supposed to be added when the appropriate tail-housing was attached prior to shipment to the dealer.

Dan

[hobi]

From what I have been told by oldtimers GM had a parts quota for non expected items. Expected items being collision or tolerance wear and or warranty related parts, non expected parts such as certain sheetmetal according to GM data at the time or options or other parts that were not expected to be replaced before such warranty were made as a run item just as for example a run of 1000 1969 fenders a run being a pair as the cars were still being assembeled so that would constitute enough parts fenders for 500 cars this is just a example as I do not have the data that GM had for replacement parts and of coarse that varied to according to what part of the country you lived in and what time of year it was.

The fender run for example woule more than lickly be punched with no holes for embles or cornering lite option as it could be used for a couple years and a assortment of options.

[bulletpruf]

Originally Posted by Judge273

As I understand the way to decode a P0R29B tranny?

P = muncie,
0 is for year of car. 1970
R is month only 12 so not sure? But, say it is a replacement and fits all months. R does say Oct.
29 is day of month,
B is M 21?

Yep.

[bulletpruf]

I'm a bit confused. I thought "CC" stamp was for a counter case (i.e., what you got to replaced your busted Muncie case from the parts counter at the local Pontiac dealer).

I thought that a complete transmission assembly was marked "CT" for "counter transmission" or something like that.

Scott

[DANTIP]

Originally Posted by bulletpruf

I'm a bit confused. I thought "CC" stamp was for a counter case (i.e., what you got to replaced your busted Muncie case from the parts counter at the local Pontiac dealer).

I thought that a complete transmission assembly was marked "CT" for "counter transmission" or something like that.

Scott

Scott,

I attached a document in Post #1 that explains how "Service Replacement" parts/assemblies are marked according to a 1969-vintage GM Service Information Bulletin. Prior to seeing this document, I was unaware of the marking and the assigned sequence/numbering system used (This does explain why the high-dollar BBC replacement engines are all marked CE for "Chevrolet Engine" rather than what most people believe means "Counter Exchange"). This document does not explain what a "CC" marked transmission case is but it does perfectly match how my 1970 M21 is marked. I wonder whether a different marking approach was used prior to the release of the Service Bulletin mentioned? If anyone is interested in better photos of the markings, I'll find time to get some more detailed photos.

Dan

[Todd Kozak]

which side of the tail housing is the speedo on?

[turbo69bird]

my freind who sells muncies says, that sept thru october would be the previous year production. if this is correct then it would have been produced oct 1969, but information I have found seems to be contradictory in that it was only 67 68 that worked this way with date code and 69 thru 74 was different?

[bulletpruf]

Originally Posted by DANTIP

Scott,

I attached a document in Post #1 that explains how "Service Replacement" parts/assemblies are marked according to a 1969-vintage GM Service Information Bulletin. Prior to seeing this document, I was unaware of the marking and the assigned sequence/numbering system used (This does explain why the high-dollar BBC replacement engines are all marked CE for "Chevrolet Engine" rather than what most people believe means "Counter Exchange"). This document does not explain what a "CC" marked transmission case is but it does perfectly match how my 1970 M21 is marked. I wonder whether a different marking approach was used prior to the release of the Service Bulletin mentioned? If anyone is interested in better photos of the markings, I'll find time to get some more detailed photos.

Dan

Ok, has anyone else seen one with a "TO" stamp? I understand what you posted, but this is new to me. I called the guy who did the Muncie for my 70 and he said he had never heard of it. He's one of the top Muncie guys in the country, so he's seen a few of these.

Scott

[DANTIP]

Originally Posted by bulletpruf

Ok, has anyone else seen one with a "TO" stamp? I understand what you posted, but this is new to me. I called the guy who did the Muncie for my 70 and he said he had never heard of it. He's one of the top Muncie guys in the country, so he's seen a few of these.

Scott

Scott,

This is the only transmission I have heard of marked like this. I too called a well know builder and he had never heard of a Muncie marked like this. I just checked Ebay and there are three "high-value" Big-Block Chevrolet replacement blocks (1-'68, 1-'70, and 1-'71) and all of them follow the marking scheme explained in the GM service bulletin mentioned in the first post (one is item #330706370971). I have ZERO doubt this transmission is an untouched (never blasted, cleaned, messed with) original. The original owner of my car is 83 years old and told me he bought this transmission as a full transmission assembly from a GM dealer. I suspect GM provided vastly more replacement engines than transmissions and most builders have never seen/noticed one.

[Todd Kozak]

Originally Posted by jimwankers

which side of the tail housing is the speedo on?

so is it driver or passenger side?

[DANTIP]

Originally Posted by jimwankers

so is it driver or passenger side?

The speedo is on the driver's side. I assume the Muncie plant would be told which tail shaft to use/install before shipment.

Dan

[DANTIP]

Originally Posted by bulletpruf

Ok, has anyone else seen one with a "TO" stamp? I understand what you posted, but this is new to me. I called the guy who did the Muncie for my 70 and he said he had never heard of it. He's one of the top Muncie guys in the country, so he's seen a few of these.

Scott

Here is a Craigslist ad for a Muncie that has the markings of a Service Replacement. The stamping shows T8 37337 and the case date stamp is P8R20. This is consistent with the GM service bulletin and with the markings on my '70 M21. It is not advertised as a Service Replacement but it is certainly marked as one.

[Todd Kozak]

I have a '661' case service-replacement M21 transmission stamped ' CCO 45571'. It has pass side speedo.I dont know what it was originally intended to service.