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Vintage GM 8 3 speed corvette transmission

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Hi Everyone,

 

I recently came across this transmission in my grandfathers garage, I believe it's for a GM 8 3 speed corvette. That said I've attached a handful of pictures and was hoping you can help me identify it, possibility letting me know if it has any value and where I could sell it. I really appreciate it, thanks in advance.

 

 

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Fox, ONE thing is for sure, that shifter was not designed for use in a Corvette, period. Corvettes used really short shifters, since the driver's seat was so low relative to the transmission location. 

 

The transmission certainly looks like a GM 3-speed of the period, but was no different in a Corvette than with most other GM stick shift cars, if I recall correctly. 

 

Your fourth photo down shows some numbers on the side. The bottom set of numbers appears to be a production CASTING date code (denoted by the impressions of the heads of screws at each end, which held the date code numerals in the production mold). It's pretty hard to read those numerals in your photo, but they MIGHT be "A176." If so, the GM production date code system TYPICALLY breaks down as "A" = the first month, January, and "17" is normally the day of that month, and "6" would represent the last number of the year, as in 1956 or 1966. If you take a light wire brush to those numbers and photo them again, we can be more sure of what we're seeing. Also clean off the other numbers on the main housing, as this may help us to further ID the trans. 

 

Next start looking around for ASSEMBLY date codes, which are not cast, but rather are stamped into the housing. These codes sometimes include application information. If you can find those stamped in digits and get a good photo, I'll try to help you with them. 

 

Also keep in mind that often, a transmission might have been removed from a Corvette at some point, but that doesn't mean that transmission started life IN a Corvette. There were many busted manual transmissions back in the muscle car years. Ask me how I know! LOL

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By the way, can you flip the transmission over, and photo the side with the shift levers, please? 

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Hi Everyone,

 

I recently came across this transmission in my grandfathers garage, I believe it's for a GM 8 3 speed corvette. That said I've attached a handful of pictures and was hoping you can help me identify it, possibility letting me know if it has any value and where I could sell it. I really appreciate it, thanks in advance

IMG_6550.JPG

IMG_6553.JPG

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fc,

          I might be able to help you with this but the images of the numbers are not clear enough. Can you wire brush them off or wet them and re-shoot please?

Greg

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Yes, without the numbers, a little difficult.

I'm going to guess 1956 full size platform trans.

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Sorry, a little too difficult to read.

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Ok I’ll try and do what you recommend but from what I can make out it say the below. 

 

GM 8

3868986

GR176

 

&

 

8880041

 

 

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Fox, I'm GUESSING that you're misreading those first two characters. I wouldn't be surprised if that first character is not a "G" at all, but rather the double-reverse impression of a slotted screw head (which holds the removable code-number plate during the molding process). The next "character" would normally represent the month of the year. And since there are only 12 months, I have never seen an "R" in that positiion. The closest character to a capital "R" in the fonts used by GM at the time would likely be an "A," as I mentioned before. 

 

IF I am correct about this, then the code is likely "A176," which would translate to January 17th, of either 1956 or 1966. So I suggest that you should look for those stamped-in numbers I mentioned before, and wire brush them clean. Also, let us have a look at the linkage side of the main housing, please. 

 

After that, we may be able to assist you. 

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Thanks for the heads up and my apologies for the delay as it appears I'm only allowed to respond to a certain amount of comments a day.

I will do what you suggested and wire brush / wet and circle back. Give me a week or so as I have it stored at a family members garage. Out of curiosity if it was either of the two you mentioned above, do they have any value? I'm just curious if I should just scrap them or are they worth more to someone who needs it.

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Condition is everything, Fox. If you have a 1956-dated GM 3 speed in excellent mechanical condition....then yes, it is certainly worth something to someone who needs it for their original car (most hot rodders and modifiers would prefer a 4 speed, automatic, or one of the new 5 or 6 speed trannies). But if you had a correct original resto project car which needed a good working 3 speed with correct date codes for your car, you would be happy to pay 2-3 hundred dollars for the "right" unit. But until a professional trasmission guy pulls the side cover off and gives it a good inspection, you won't know what condition it really is in. 

 

Don't forget to seek out those STAMPED-IN Assembly Date Code digits. These can SOMETIMES tell you which decade (56 or 66), and sometimes tell you a bit more about the application. I would ASSUME that a 1956-dated 3 speed trans in good shape might be a bit more desirable than a 1966 unit. But that is just speculation on my part. 

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Might those stamped-in date codes be in the flange under the cover?

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Posted (edited)
7 hours ago, Spinneyhill said:

Might those stamped-in date codes be in the flange under the cover?

The Assembly date code on 1964 and older 3 speed Saginaw transmissions destined for use in Chevrolet vehicles is normally stamped into the machined surface at the rear of the main housing, which the extension housing bolts to. It is normally visible even when the transmission is assembled, on the passenger side. So if you're under the car on a hoist, you would stand to the passenger side of the car, just behind the transmission, and look (towards the front of the vehicle) at the exposed portion of that machined main-housing surface where it mates to the tail housing. The number is usually stamped sideways, so you would cock your head to read it. 

 

 

 

Edited by lump (see edit history)

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Posted (edited)

Ok, I dug out my books and did a little research.

 

IF I am reading your (not-easily-deciphered) CASTING numbers correctly, this transmission is a 1966 or 1967 light duty or standard duty 3 speed Saginaw unit. The casting numbers on your main housing and extension housing were not used for 1965 and older transmissions, and the main housing not used in 1968-up.  

 

Note that the casting date code ends in a "6," which indicates the production year for the casting process of the iron housing. The stamped-in ASSEMBLY Date Code will tell you when the transmission housing was machined and the transmission assembled into a functional unit. NORMALLY a rough GM casting will be machined and assembled into a finished unit during a period from one week to a couple of months after it was cast. So, ASSUMING I am right about your first digit of the casting date code being an "A," then it would indicate this transmission was completed in the late winter or early spring of 1966. Since GM's changeover to new model vehicle production took place in July back in those days, it would be expected that this transmission was intended for a later production 1966 model-year vehicle. But if I am wrong about that first letter, it would be possible that it was made later in the 1966 model year, and thus intended for a 1967 model vehicle. 

 

The reason I had hoped to see the driver's side of this transmission is that 1965 and older 3 speed Saginaw transmissions used a 4-bolt side cover. 1966 and newer Saginaw 3-speeds used a 7-bolt side cover. And the main housing of 1966 and newer Saginaw 3 speeds is larger than 1965 and older units. All of these things added together make identification of the age of your 3 speed Saginaw fairly certain.

 

The good news is that 1966 and newer Saginaw 3-speeds were fully synchronized, unlike earlier units. The not-so-good news is that the stamped-in ASSEMBLY Date Code numerals are not necessarily in the location I mentioned above. That is the first place I would check, but if not visible there, you'll need to keep searching. But, depending on what vehicle plant installed this transmission, the Assembly Date Code MIGHT give you some additional data. 

 

Still looking forward to clear photos of all numbers, and a view of the driver's side of the main housing. I may be able to provide further help once I see all that. 

 

Edited by lump (see edit history)

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Hi lump,

 

I tried to clean up the numbers for calcification but forgot to take a picture of the other side. Let me know what you think but I can take more pictures this Friday.

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Definitely  January 17 1966 casting date. Not a particularly valuable unit. I have seen them anywhere from $50.00 to $250.00 and even at the lower end not very hot sellers.

 

Greg in Canada

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Again, we really, really need to see the STAMPED-IN numbers which I told you about before, and the driver's side with side cover. We already had these numbers figured out. 

 

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Sorry, I didn't mean to jump in where I shouldn't. Is there still a possibility this is a more desirable Trans. than it would appear  ? Or are you like many of us and like to know the whole story on the specifics of a given part ? I know the devil is in the details.

 

Greg in Canada

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The main case and extension housing (tail housing) have casting numbers which are well documented for years-of-use, etc. There is no application data in the casting numbers anywhere on these units. However, SOMETIMES the stamped in "Assembly Date Code" digits have some application data. Without that, all we know is that it was intended to be assembled as a light duty, or "standard duty" 3 speed in the 1966 or 1967 model year. 

 

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