on the 66 ss396 Ive been decoding, ive came across something strange. I just got my 66 chevelle info cd in and it shows that the break down of my cowl tag as

W2LGSR My concern is the "L." The CD shows that the L code stands for M20 4 speed. My car doesnt run because the engine is apart so there is no way to tell without cracking open the transmission, but WHY would anyone pair an M20 with a "KM" 4.56 rearend? The car was purchased to drag race back in the 60s but isnt an M20 with 4.56 too ridiculus? Is it possible that the "L" stands for M21 or M22? Thanks a lot in advance.

L stands for 4 speed and that is all we know for sure. Only 12 M-22's were reported to be installed in 66's. So the chances of you having one are very limited, especially with a car that is a basic 325hp car if I recall correctly. The qquestion is not why would someone order an M-20 or M-21 with that rear, but why would they order a 325HP??? or for that matter why would they order a 360hp??

I have documented atleast 6 and possibly 7 of the known M-22's installed and all were in 66 SS L-78 cars. Just my thoughts, hopefully others will give their thoughts. The truth will be in that Trans when you get it and crack it open!

Mike Crown

Ok, so the "L" didnt always mean M20 then? It only meant 4 speed? Thanks a lot.

Also note
M20 does not stand for a Muncie trans. It can be but its the regular production option code for all 4 sp trans weather Muncie, Saginaw, Borg-Warner or whatever. The brand of transmission used was determined by Chevrolet.

Many don't know this and think the M means Muncie.

Also note
M20 does not stand for a Muncie trans. It can be but its the regular production option code for all 4 sp trans weather Muncie, Saginaw, Borg-Warner or whatever. The brand of transmission used was determined by Chevrolet.

Many don't know this and think the M means Muncie.

To further clarify what Mike said... For 1966, the Chevelle/Chevrolet "RPO M20" does indicate just the 4-speed transmission... Saginaw or Muncie depends on the engine... A Malibu with a 283 and a factory 4-speed recieved a Saginaw, but it was still RPO M20...


Back to the original post; Its been a while, but did the basic order form even specify M20/M21 (or just M20)? Unless you were in-the-know a actually specified the trans (such as with the M22, etc), I think the M21 was just what was "automatically" installed when 3.73s-4.88s were ordered...

Wasn't '66 the first year for the M21? If so, how many people would know to order this trans with the lower gears, and the M20 with higher gears?

In '66 did most people know to order "M20" or "M21", or just to order a "4 speed"? Alot of people didn't even know the L78 was an option, as it wasn't always publicized or promoted by the dealers...

Did not the 66 & 67 Kansas chevelles get the "Q" option code for the M21 4 speed?

Did not the 66 & 67 Kansas chevelles get the "Q" option code for the M21 4 speed?

I think Kansas and Atlanta both got the "Q", and this is an Atlanta-built car if I recall correctly...

Are we sure its the original rearend, and that its 4.56's?

With a 325HP engine, it does seem odd to me...

there is no way to tell without cracking open the transmission

After 42 years, there's no way to tell the trans hasn't been opened before (and gears replaced) anyway...

Fisher's production was controlled by GM's need to fill dealer orders for certain models with a variety of equipment. In some cases the bodies had to be made differently to accommodate different options, some installed by Fisher, most later on the Chevrolet assembly line. The point is, although Fisher built bodies to accept a variety of Chevrolet options, their own body labeling method, the cowl tag, contained information that only related to the body itself. Fisher Body, through the use of the cowl tag, provided information on each body in 8 separate categories. The information on the cowl tag was not placed on the cars for the benefit of the assembly line workers who were building the car, (they used the Production Broadcast Notice, or "build sheet", as most people call it); it was meant to be a permanent record of the way each body was manufactured for purposes of later identification for dealer servicing, or warranty claims. It also protected the manufacturer against possible safety or legal claims, considering that over the life span of these cars equipment might be changed.

Weather the car got a M20, M21 or M22 they body never changed so there was no need for a M21 or M22 code.

These body codes are not gospel. Many inconstancies between model years, plants and divisions. Once the body was delivered to Chevrolet, they could have cared less what was on the tag. Once the body was received in the body bank and processed, everything from then on was controlled by the Plant Broadcast system and its paper instructions, the build sheet (known as the Broadcast Copy).