I have a '78 4-speed. In doing some research, I found that there were 2 potential gearings. One was a 2.64:1 (M20 RPO code) and the other was a 2.43:1 (M21 RPO code). There is a reference to a ZU stamp on the former and a ZW stamp on the latter ("...on the lower half of the casing"). I have the transmission out but don't see either code anywhere that I can see (but it is crusted up with oil). Here's what I can see where I cleaned off the gunk:

Borg-Warner
13-04-066-903

Casing lettering
WB 2882
18S424412

Cover lettering
8-13-78
Q7
13-04-097-901

on the passenger side the marks include
13 04 065 906
W.G.Div.
FpC1

This is an amazing Forum and I suspect one of you will know the answer so thanks in advance!

 

you are correct about the letter codes, check again after you clean it

http://corvette-world.com/corvette_1...on%20Codes.php

 

MelWff,
Thanks for the reply! I have been taking a bath in stuff to clean the crud but can't find this code I'm looking for. I'm assuming it is on the actual transmission case, not the output end. Correct? But can anyone zero in on the area I might find this info?

 

I picked up a Corvette 1968 - 1982 Restoration book over the past weekend and it is a good guide. The date and manufacture code is located on the Drivers Side Flange of the tranny adjacent of where it attaches to the rear tail housing. Your case lettering is the number your looking for the last number 1 is a wide ratio and the number 2 is the close ratio transmission.

WB 2882 it was build in Feburary 28th of 1978 and the last number 2 is the close ratio transmission.

W is the Borg Warner

B is the Month code Feburary

28 is the day

8 is 1978

2 is the Close Ratio Transmission code.

 

MakoJoe,
THANK YOU VERY MUCH!! You nailed it for me!

 

Almost

The last number is the shift, not close or wide:

http://www.hunt4cleanair.net/Articles/fourspeeds.pdf

More info (input groove):

http://www.pontiacpower.org/BW.htm

You could also order an invoice ($50) and it will tell what was on the car when it left the factory. if that is your vin #24412?

 

Yes on the VIN #. I guess this qualifies as a numbers matching part and your suggestion about getting the invoice makes sense. Thank you!

 

I have been reading as much as I can about this topic and here is a compilation of information I found in various sources. I thought I would share this with the group and if corrections are needed, I hope you will weigh in. Here are some findings and please note that these apply just to my 1978 L82. Your results may vary.

The transmission is a Super T10 Borg Warner. GM started installing these transmissions around January to April 1974 and this transmission replaced the older T-10 and Muncies.
It has an aluminum case.
Borg Warner manuals are distinguished by a 9-bolt side cover.
There are various stamp and casting numbers but it appears that they all start with 13-04 which is a Borg Warner manufacturing number.
The tailshaft housings are all aluminum.
A 903 designation on the id number indicates an aluminum case.
The ZU and ZW letters were painted on the lower part of the main case and were likely rubbed off in manufacture.
The input shaft at the front has grooves cut across the splines. If you have 2 grooves your transmission has a 2.43 first gear. If you have 3 grooves, you have a 2.64 first gear.
If you ordered the L82 and the 2.43 (M21/close ratio) you got the 3.73 rear end and I suspect this was the performance combination.
I found consistency for the coding of the 9 bolt cover which was 13-04-097-901 but this should be confirmed.

There are still some things I don't know. There are different numbers in groups of 3 in the casting or stamping on these transmissions. I don't know what the final 3 numbers are but they seem to be 901, 902, 903, etc. etc. One reference indicated that these numbers may pertain to the composition of the material, that is, iron or aluminum or other.
I also have a casting code on my transmission of 13-04-066-903. I believe this can be decoded as Borg-Warner (13-04) and aluminum case (903) but I have no information as to what the 066 means.

If anybody else has other data, please join in.