Transmission casting number Q

[The73vetteman]

This is one for those who really know their numbers! I have a '74 L48 with a 4 speed. It's my understanding that there were two different versions of the 4 speed - 'close ratio' and I guess standard. How can I tell which one I have?

Poking around underneath I can see what I assume is the casting number on the side of the tranny - 392566. Can anyone interpret this for me and does it signify anything about what's inside?

Thanks in advance, John

 

[George Black]

John: I can answer your question but need more information. 4 speed transmissions manuf. by Muncie were used in 73-74 corvettes. (Beginning in mid to late 74 Borg Warner Super T-10 4 speeds were used.) Two alpha numeric sequences are stamped into the main case on a vertical surface at the front of the right side. One of the numbers is a derivative of the cars serial number.(This appears to be the number you provided). The other number is a production code and the date the trans. was originally assembled.

The production code begins with a letter to indicate the source of the trans. An example production code would be "P3M18A". This indicates a M-20 wide ratio Muncie 4 speed assembled on Aug. 18, 1973.

P is for Muncie. 3 represents last digit of model year. Next is month of production followed by two numbers denoting the day of the month. "A" indicates wide ratio M-20 with 2.52 first gear ratio. (B is close ratio; C also denotes close ratio).

In mid 1974 "W" used to indicate Borg Warner.

Find your complete production code and I will translate it for you.

 

[mvftw]

A quick to tell the diffenence is to look at the side cover (drivers side) 7 bolts = Muncie, 9 bolts = ST-10

 

[JohnZ]

The Muncie "P"-code you're looking for is stamped vertically on a raised rib at the rear of the passenger side of the main case, just forward of the joint to the bearing retainer and tailhousing.

 

[The73vetteman]

Thanks for the info guys. After another rummage about underneath I found two sets of numbers stamped on that passenger side rib. One matches the VIN number, the other is P3D27A. Following the key provided by George I interpret this to be an M-20 wide ratio Muncie assembled April 27 1973. That matches in terms of dates with the block casting number and the VIN.

Thanks again guys, I am now a slightly more knowledgeable Vette owner!

John

 

[George Black]

John: You are correct--you have a Muncie M-20 wide ratio assembled April 27, 1973! Glad to have helped. I am not a numbers fanantic, but sometimes it is interesting to decipher the "code system" used by GM. Sorta like solving a puzzle at times.