1/2 ton factory 2.41 gears!

[Desert1957]

Originally Posted by Keith Seymore

I don't recall building any TH375s, or seeing them mixed in with the stock on the floor.

In this context I believe the MX1 refers to the TH400 (merchandised RPO for a non-overdrive automatic; MX0 being an overdrive automatic). MM3 and MM4 are Saginaw three and four speeds, respectively, and MM7 is the New Process overdrive manual MY6.

The Saginaw 3 speed was offered with two first gear ratios, depending on the application (M62 and/or M64), column shifted.

K

Interesting, My RPO code was M40. I am sure it was the original trans because I was friends with the owner. Looks identical to a Turbo 400 but has the long tail stock and shaft of a 350. 375 is stamped on the case.
Pan is a typical turbo 400 because I swapped it for a deep pan before towing.

Here is some more info I found.


Turbo Hydra-matic 400

The TH-400 or Turbo 400 was a three-speed automatic transmission first introduced at the beginning of the 1964 model year in Cadillacs and Buicks (under the name Super Turbine 400). In the following year, Oldsmobile and Pontiac and some full-sized Chevrolets received it.

The TH 400s produced in 1964-67 were equipped with a torque converter that incorporated the Switch-Pitch variable-pitch stator, which allowed variable torque application at start off and cruise. These can be identified outside the vehicle by the kick down switch on the tranny which has two prongs instead of one. His concept actually came from the Buick "Twin Turbine" Dynaflow transmission used from 1955 through 1963.

The TH 375, is simply a TH 400 with a long output shaft that mates to the smaller TH 350 drive shaft yoke. This can be identified by "375-THM" cast into the tail housing. Internally the clutch packs originally had fewer friction plates. The 375 rating was a result of the smaller yoke and fewer clutch friction plates.

To confuse the matter, some heavy duty TH 350s were also designated THM375-B. The key to telling the difference is the shape of the pan. Later, there was a 3L80HD, which is sometimes referred to as a "Turbo 475". This 3L80HD has a straight-cut planetary gear set and there is no externally visible way to determine whether the transmission contains the straight-cut planetary gear set. Some 3L80HD units had an extra deep oil pan, but it is not a reliable indicator. The TH 425 front wheel drive transmission of the Toronado and Eldorado shares almost all its internal parts with the TH 400.

Your best bet for identification is the transmission oil pan.

By 1980, usage of the TH 400 in GM passenger cars started to decline. The demand for better gas mileage convinced GM to design a 4-speed auto, with 4th gear being overdrive. By 1984 GM passenger cars no longer used the TH 400. From 1984 through 1986 the C- and K-series full size Chevrolet/GMC pickups and G-series vans. Thereafter it was renamed to the 3L80 and used more in heavy duty applications. The United States Army HMMWV is the only vehicle using the 3L80. The civilian Hummer H1 originally used the 3L80, but since the mid 1990s the 4L80E was used.

Here is the full article link

http://wildaboutcarsonline.com/cgi-b...=9990364942279

Desert