Post by corvetteguy on Jun 9, 2011 10:52:26 GMT -6
Recently, we received the following email which asked some very good questions about how to identify whether a 3 speed transmission for a 1959 Corvette was the original transmission. We thought we'd include the email question here and our response with the hopes that others might be able to use this information as well.
Here is the original email. (We have removed all personal information to protect the privacy of the original sender.):
"I have a 1959 Corvette with a replacement motor. The transmission is a 3 speed which may be original.
The main case is marked:
GM
8
3743868
K118
The tail housing is marked:
GM 1
1188
3787450
The shift cover plate has a 4 bolt pattern and is marked:
3781811 GM
Can anyone offer any information regarding this transmission? Is it original for a 1959 Corvette? Where can I find the information?
Thanks for your help.
And our response:
Good Morning,
Thanks for contacting Corvsport.com with your questions about the transmission in your 1959 Corvette. After doing some research on the numbers you sent us, it does appear that you have a numbers matching OEM transmission. The information included here was compiled from a number of resources including the original AMA Specifications (circa 1959) that were recorded for your vehicle.
To start, the 3-speed manual transmission did come as the standard, factory-installed transmission in 1959. While a 4-speed Powerglide transmission was also offered (RPO 313), it was only installed in 1,878 of the total 1959 Corvettes built (roughly 19%). The overwhelming majority of 1959 Corvettes did come with a a 3-speed manual transmission.
To identify the originality of the 3-speed in your car, there are a number of clues you can look for, some of which you included in your email to us.
First, the location of the stampings: On a 3-speed transmission, the stampings should be on the upper right corner of the rear face of the transmission.
Second, the stamping numbers you sent us are a big clue:
You stated that the main case was marked with a GM (General Motors), an 8, and the part number 3743868. Working in reverse order, the "374" prefix in the part number is consistent with the 1959 Corvette. When you look at many of the components installed during that era, including driveshafts, etc., the 374 prefix is commonly used and fits the time period. The one item I would encourage you to re-check is the stand alone "8". Is it possible that the number "8" is actually the letter "S"? If so, the "S" would indicate a "Saginaw" transmission, which was the factory 3-speed transmission (with overdrive.)
Perhaps the most relevant piece of information though, at least when it comes to placing the time period and the authenticity of your transmission is the "K118" stamping. The "K118" is actually a date code. Translated, it mean that your trans was built in November (K is the 11th letter of the alphabet - A=January, B=February, and so on), 11 is the day, and 8 is the year (as in 1958). So, put together, your transmission was manufactured (or at least completed) on November 11, 1958, which makes it VERY probable that it was built for the 1959 model year.
Similarly, the GM 1 cast on your tail housing is consistent with OEM General Motors tail housings and, again, the date code of I188 (the first digit should be the letter I, not the number 1 - (please re-check as your email indicated the number 1)), would indicate that it was manufactured on September 18, 1958, again consistent with the time frame.
We cannot readily confirm the originality of the shift cover plate, but it seems probable that, again, based on the stamped part number, it is circa 1958-1960.
We hope this helps!
Scott & Garin
Site Developers and Owners
Corvsport.com
Here is the original email. (We have removed all personal information to protect the privacy of the original sender.):
"I have a 1959 Corvette with a replacement motor. The transmission is a 3 speed which may be original.
The main case is marked:
GM
8
3743868
K118
The tail housing is marked:
GM 1
1188
3787450
The shift cover plate has a 4 bolt pattern and is marked:
3781811 GM
Can anyone offer any information regarding this transmission? Is it original for a 1959 Corvette? Where can I find the information?
Thanks for your help.
And our response:
Good Morning,
Thanks for contacting Corvsport.com with your questions about the transmission in your 1959 Corvette. After doing some research on the numbers you sent us, it does appear that you have a numbers matching OEM transmission. The information included here was compiled from a number of resources including the original AMA Specifications (circa 1959) that were recorded for your vehicle.
To start, the 3-speed manual transmission did come as the standard, factory-installed transmission in 1959. While a 4-speed Powerglide transmission was also offered (RPO 313), it was only installed in 1,878 of the total 1959 Corvettes built (roughly 19%). The overwhelming majority of 1959 Corvettes did come with a a 3-speed manual transmission.
To identify the originality of the 3-speed in your car, there are a number of clues you can look for, some of which you included in your email to us.
First, the location of the stampings: On a 3-speed transmission, the stampings should be on the upper right corner of the rear face of the transmission.
Second, the stamping numbers you sent us are a big clue:
You stated that the main case was marked with a GM (General Motors), an 8, and the part number 3743868. Working in reverse order, the "374" prefix in the part number is consistent with the 1959 Corvette. When you look at many of the components installed during that era, including driveshafts, etc., the 374 prefix is commonly used and fits the time period. The one item I would encourage you to re-check is the stand alone "8". Is it possible that the number "8" is actually the letter "S"? If so, the "S" would indicate a "Saginaw" transmission, which was the factory 3-speed transmission (with overdrive.)
Perhaps the most relevant piece of information though, at least when it comes to placing the time period and the authenticity of your transmission is the "K118" stamping. The "K118" is actually a date code. Translated, it mean that your trans was built in November (K is the 11th letter of the alphabet - A=January, B=February, and so on), 11 is the day, and 8 is the year (as in 1958). So, put together, your transmission was manufactured (or at least completed) on November 11, 1958, which makes it VERY probable that it was built for the 1959 model year.
Similarly, the GM 1 cast on your tail housing is consistent with OEM General Motors tail housings and, again, the date code of I188 (the first digit should be the letter I, not the number 1 - (please re-check as your email indicated the number 1)), would indicate that it was manufactured on September 18, 1958, again consistent with the time frame.
We cannot readily confirm the originality of the shift cover plate, but it seems probable that, again, based on the stamped part number, it is circa 1958-1960.
We hope this helps!
Scott & Garin
Site Developers and Owners
Corvsport.com
