Engine and Driveline
Transmissions
For the first time since 1966, a manual 3-speed transmission was not the base transmission for either the SS396 or the SS454. A mandatory transmission choice was one of the three Muncie 4-speed manual transmission or the Turbo-Hydramatic 3-speed automatic transmission.
Transmissions are dated coded just like most major components. The format of the build dates vary depending on the transmission type and where it was built.
The Muncie manual 4-speed went through 3 date variations from 1963 through 1972. From 1963 through 1966 the Muncie date included only the month and day such as P0110 where “P” is the code for Muncie, 0110 is January 10. In 1967 and 1968, the date code got a year designator and a letter designator for the month such as P8A01, meaning 1968 (8), January (A) 1st (01). Note that a Muncie dated with a September to December build date was actually built the prior calendar year. An example would be the date code P8T13, meaning 1968 (8), December (T), 13th. The transmission was assembled December 13, 1967 for the 1968 model year. Likewise a P8S28 stamp means 1968 (8), September (S), 28th of the calendar year 1967 for a 1968 Chevelle. The 1969 and later Muncie date stamps included a suffix letter “A,” “B,” or “C” noted the specific type. The letter “A” representing the M20 wide ratio version, the letter “B” representing the standard duty M21 close ratio version, and the letter “C” representing the heavy duty M22 close ratio version. A sample might be P0C25B for Muncie (P), 1970 (0), March (C) 25, M21 (B). Muncie month letters are not sequential for some reason but rather it skips letters. In addition, a partial VIN is stamped on the transmission to identify the car in which the transmission was originally installed and the broadcast code is ink-stamped on the case.
Note the "WC" stamp broadcast code to identify the Muncie 4-speed
variation, in this case the RPO M22.
A Muncie shifter assembly is one item you may not pay too much attention to but judges certainly will.
Muncie 4-speed transmission shifter assembly disassembled for cleaning
and refurbishing. It’s recommended this be rebuilt in one setting as
there are many small parts that could get lost or their locations forgotten
over time.
Muncie 4-speed transmission shifter assembly after cleaning is reassembled
on the transmission and bolted to the chassis. Note the extra transmission-to-chassis
support to combat engine torque.
The Turbo-Hydramatic 400 (TH400) has a metal plate riveted to the side of the transmission case to identify its assembly date, its application, and its serial number. Different TH400 transmissions were used based on the horsepower rating of the engine; the lighter duty L34 and LS5 engines would get a lighter duty transmission than the L78 and LS6. The date is in Julian calendar format. The Julian date is for a calendar year and not the particular model year so it is not uncommon to see dates in the 500-570 range. For example, a Julian date stamp on a 1970 model year transmission like 413 means the 413th day counting from January 1, 1969 - or February 17, 1970 along with the transmission’s assigned serial number.
The TH400 was only used with the 1970 402/454 engines. 1971 and 1972 350 engine SS optioned Chevelles used the RPO M38 TH350 for their automatic transmission choice.
Each TH400 automatic transmission has an identification tag riveted
to its case. The letters (“CY” in this instance) depict particular application
for the transmission. The transmission’s assembly date and serial number
are found on this identification tag and tags are color coded for their
intended use.
Often the colors have worn away but the critical data remains.
The date (419), the application letters (CF in this instance), and
the transmission's serial number.
A partial VIN stamp is also found on the TH400 transmission just above the oil pan rail on the passenger side to identify the car in which the transmission was originally installed. Another variation on the TH400 is the oil pan and the associated transmission filter. Early 1967 TH400 transmission oil pans have a “heel mark,” a bump, and 3 dimples. A Chevrolet Service News Bulletin around July of 1967 indicates a change in the design that eliminated the “heel mark,” the bump, and reduced the dimples from 3 to 2.
Early 1967 TH400 Turbo-HydraMatic automatic transmission oil pan.
Note the dimples on the pan, both the number and locations. This should
NOT be used on later TH400 transmissions as the oil filter and screen
are different than later model TH400 transmissions.
Transmission oil pan for M40 TH400 Turbo-HydraMatic automatic transmission
is left neutral and not painted. Note the number and location of the
two dimples in the oil pan.
Various plate colors and prefix codes were used for TH400 applications. These codes and colors have been found so far.
| Broadcast Code/Engine | Year/HP |
| CC - 396/402 | 1967-1969 325hp |
| CD - 396/402 | 1968 - 350hp 1970 - 330hp (LS3) 1971 - 300 hp 1972 - 240hp |
| CE - 396/402 | 1969 - 350hp |
| CF - 402/454 | 1970 - 350hp 1971 - 365hp 1972 - 240hp |
| CR - 454 | 1970 - 360hp(1) |
| CS - 454 | 1970 - 360hp |
| CW - 402 | 1970 - 375hp |
| CX - 396 | 1969 - 375hp(2) |
| CY - 454 | 1970 - 450hp |
(1) Found on Van Nuys LS5s prior to at least 01-14
(2) Also reported on 1969 427 COPO
The Turbo-Hydramatic 350 was introduced in 1969 and was used in SS Equipment in 1971 and 1972 (as well as non-SS Equipment) Chevelles. The TH350 was built at 2 transmission plant facilities in the United States, Cleveland, OH. Toledo, OH. Cleveland-built TH350 transmissions are identified with the letter “B” and Toledo-built TH350 transmissions are identified with the letter “Y” on owner Protect-O-Plate warranty cards. GM of Canada TH350 transmissions from McKinnon Industries in St. Catharines use the letter “E” on warranty cards. These are dated in the format of the plant letter, the model year, a letter for the month, and 2-digit date such as Y1K25 for Toledo-built TH350 (Y), 1971 (1), July 27 (K27). Like the Muncie 4-speed manual transmissions, month letters are not sequential for some reason but rather it skips letters.
Whether you are restoring an automatic transmission or manual transmission car, now is a good time to refurbish that shift linkage.
