{"id":375,"date":"2013-01-27T00:27:00","date_gmt":"2013-01-27T06:27:00","guid":{"rendered":"http:\/\/www.apatco.com\/corvette\/?page_id=375"},"modified":"2014-09-25T23:09:10","modified_gmt":"2014-09-26T05:09:10","slug":"transmission-and-differential","status":"publish","type":"page","link":"https:\/\/www.apatco.com\/corvette\/?page_id=375","title":{"rendered":"Transmission and Differential"},"content":{"rendered":"

The 1973 Corvette car came with a Tubro 400 Transmission, which I had rebuilt in Winnipeg at UltraTransmission<\/span><\/p>\n

GM\u00a0TH400 Automatic Transmission<\/h1>\n

The TH400 is an automatic shift, three-speed, longitudinally positioned transmission. It is widely regarded to be a supremely durable and legendary transmission.\"400<\/a><\/p>\n

The TH400 is conservatively rated at 450 ft. lbs. of input torque. Aftermarket building techniques take it well past that figure.<\/p>\n

History<\/strong>
\nThe Turbo 400 was introduced in 1964 in Buick and Cadillac cars and in Chevrolet and Oldsmobile cars the following year. An innovative variable pitch stator was available in the 1965-1967 cars that could essentially vary the characteristics of the torque converter. The design remained almost completely unchanged from its inception to 1991, but it was renamed 3L80 in 1987.<\/p>\n

Exploded View<\/a><\/p>\n

<\/p>\n

The THM400 can be visually identified by an oil pan number four shown at\u00a0Transmission Pans<\/a>. First introduced for the 1964 model year under the name “Turbo Hydra-Matic” in Cadillacs.[3]<\/a><\/sup>\u00a0and “Super Turbine” in Buicks.[4]<\/a><\/sup>\u00a0The following year, application expanded to Oldsmobile and\u00a0Pontiac<\/a>\u00a0and to some full-sized Chevrolets. Many of the Buick, Cadillac, and Oldsmobile THM400s produced between 1964-67 were equipped with a Switch-Pitch\u00a0torque converter<\/a>\u00a0variable-pitch\u00a0stator<\/a>, which is sought after by collectors and drag racers. These can be identified outside the vehicle (with the torque converter removed) by a narrow front pump spline. Externally the switch pitch version has two electrical connections, where the non-switch pitch THM400 has only one. GM used a Switch Pitch torque converter in the\u00a0Buick<\/a>\u00a0twin turbine\u00a0Dynaflow<\/a>\u00a0transmission between 1955\u20131963 and the\u00a0Super Turbine 300<\/a>\u00a0two speed transmissions used by\u00a0Oldsmobile<\/a>\u00a0Pontiac, and\u00a0Buick<\/a>\u00a0divisions between 1964-1967.<\/p>\n

A variant of the THM400 known as a THM375 is a THM400 with a long output shaft that mates to the smaller THM350 drive shaft yoke. It can be identified by “375-THM” cast into the tailhousing. Internally the clutch packs originally had fewer friction plates. Some “Heavy Duty” THM350s were also designated THM375-B. Another variant is the 3L80HD, often referred to as a Turbo 475. The 3L80HD has a straight-cut planetary gear set. There is no externally visible way to determine whether the transmission contains the straight-cut planetary gear set. The\u00a0THM425<\/a>\u00a0front wheel drive transmission shares almost all its internal parts with the THM400.<\/p>\n

By 1980, the relatively heavy THM400 was being phased out of usage in passenger cars in response to demand for improved fuel economy. The Presidential Limousine used during the\u00a0Reagan<\/a>Administration, a modified 1984\u00a0Cadillac Fleetwood<\/a>\u00a0Brougham, was the last known GM passenger vehicle to use the THM400. The THM 400 was utilized in the C- and K-series (full size) Chevrolet\/GMC pickups and G-series (full size) vans until 1990 when GM switched over to the 4L80E. Today, the\u00a0United States Army<\/a>\u00a0HMMWV<\/a>\u00a0is the only vehicle using the THM400. The civilian\u00a0Hummer H1<\/a>\u00a0originally had the 3L80s, but the current model has had a 4L80E since the mid-1990s.<\/p>\n

Through the end of the ’70s substantially more CBOP (Cadillac\/Buick\/Oldsmobile\/Pontiac) bellhousing THM400s were produced than any other THM400. Chevrolet bellhousing THM400s, while not rare, can be hard to find and are, as a result, usually more expensive to buy. Other bellhousing patterns are, accordingly, rarer. The THM400 was never produced with a multicase\u00a0bell housing<\/a>.<\/p>\n

Other auto manufacturers have used the THM400 and its 4L80E successor, including\u00a0Ferrari<\/a>\u00a0(in the\u00a0400\/412<\/a>);\u00a0Jaguar<\/a>\/Daimler<\/a>\u00a0(in pre-1994\u00a0XJ12<\/a>\u00a0and\u00a0XJ-S<\/a>\u00a0coupes) and their Daimler stable mates;\u00a0Rolls-Royce<\/a>\u00a0(in 1965\u20131980\u00a0Silver Shadow<\/a>\u00a0and 1980-1992\u00a0Silver Spirit<\/a>\u00a0series cars, along with their\u00a0Bentley<\/a>\u00a0stable mates); the\u00a0Nissan Prince Royal<\/a>;\u00a0AM General<\/a>; and\u00a0Jeep<\/a>\u00a0(usually found in the FSJ pickups andSUVs<\/a>). Early Jeep THM400s used an adapter between the engine and transmission bell housing while later models had an AMC specific housing. Though identical except for the bell housing pattern used through the ’60s and ending in 1979 the THM400 was mated to the Dana model 18,20 and was the only transmission used with the Borg-Warner 1305\/1339 all-wheel-drive transfer case used only in Jeeps, It has been known to adapt a THM400 to other engines using adapters.<\/p>\n

THM400 transmissions are very popular in automotive competition due to their great strength. Much of this strength comes from the use of a cast iron center support to suspend the transmission’s concentric shafts that join the clutch assemblies to the gear train. The center support, which is splined to the interior of the transmission’s case, also provides a robust reaction point for first gear (the gear train’s reaction carrier is restrained from counter-rotating the engine in first gear by a\u00a0roller clutch<\/a>\u00a0whose inner race is part of the center support). Since the first gear reactive force is evenly distributed around the periphery of the case, the types of mechanical (and some times violent) failures that have plagued other competition transmissions are rare.<\/p>\n

The THM400 was the first three-speed, Simpson-geared automatic to use\u00a0overrunning clutches<\/a>\u00a0for both first and second gear reaction, a feature that eliminated the need to coordinate the simultaneous release of a band and application of a clutch to make the 2-3 gear change. Owing to this feature, as well as the use of a large, multi-plate clutch to provide second gear reaction, the THM400 is able to withstand very high input torque and an enormous number of shifting cycles, as would be encountered in frequent stop-and-go driving. As a result, it has met with considerable success in commercial vehicle applications.<\/p>\n

For 1987, GM changed the nomenclature of their Turbo Hydramatic transmissions \u2014 the THM400 was renamed to the ‘3L80’ (three forward speeds, longitudinal positioning, and an arbitrary ‘strength’ of 80, the second highest such rating assigned). The 3L80HD was introduced in 1987 as the HD unit used in passenger trucks. In 1991, a four-speed overdrive version, the\u00a04L80-E<\/a>, replaced the THM400 in Chevrolet\/GMC pickups, vans, SUVs, and commercial vehicles. The 4L80E (and its successor 4L85E) was the first Hydramatic to incorporate electronic controls \u2014 almost all of the THM400\/3L80\/3L80HD’s components are interchangeable.<\/p>\n

Transmission fluid cooler line connections are found on the right hand side of the THM400. The lower connection is the cooler feed, and the upper connection is the return.[5]<\/a><\/sup>\u00a0The case is tapped for either self-sealing 1\/4″NPT<\/a>\u00a0fittings, or 1\/2″UNF<\/a>\u00a0fittings with a washer seal. 5\/16″ or 3\/8″ rigid coolant lines are generally connected via appropriate double-flared adapters.<\/p>\n

4-Wheel drive truck applications used a shorter output shaft that coupled with a female transfer case input shaft.Early transfer cases mated directly to the THM400 with an cast-iron adapter,usually a vertical oval shape.Later models used a circular style iron adapter which is generally considered the stronger of the two.<\/p>\n

Weight:<\/strong>\u00a0135Lbs<\/p>\n

Gear Ratios are:<\/strong><\/p>\n