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Turbo-Hydramatic


Turbo-Hydramatic is the registered tradename of a family of automatic transmissions developed and produced by General Motors. These transmissions mate a three element torque converter to a Simpson compound planetary geartrain, providing three forward speeds plus reverse.

The Turbo-Hydramatic (THM) series was developed to replace both the original Hydra-Matic models and the Buick Dynaflow. In its original incarnation as the Turbo-Hydramatic 400 it was first used in the 1964 model year in Cadillacs. The Buick version, which followed shortly thereafter, was known as the Super-Turbine 400. By 1973 THM units had replaced all of GM's other automatic transmissions (e.g. Chevrolet Powerglide, Buick Super Turbine 300, Oldsmobile Jetaway, etc.). From the early 1980s onward, it was progressively replaced by later four-speed and five-speed automatics (which incorporate an overdrive gear), some of which continue to use the "Hydramatic" trade name.

Although the Turbo-Hydramatic name is related to that of the first fully automatic transmission, Hydramatic, developed by General Motors Oldsmobile division in the late 1930s, the two transmissions were not mechanically related.

TH400 / 3L80 / 3L80HD

The THM400 (or the Turbo 400, which it is called by drag racers and car enthusiasts) was first introduced during the 1964 model year in Cadillacs and Buicks (under the name Super Turbine 400). The following year, use expanded to Oldsmobile and Pontiac and to some full-sized Chevrolets (usually coupled to the Mark IV big-block V8). It can be identified by an oil pan in the shape of what some would call similar to that of the state of Texas.

Many of the Buick, Cadillac, and Oldsmobile TH400s produced between 1965-67 were equipped with a torque converter that incorporated the Switch-Pitch variable-pitch stator, which is sought after by collectors and drag racers. These can be identified outside the vehicle by a noticeably narrower front pump spline. Externally there are no differences from the non-SP TH400.

THM400s were not the only Switch-Pitch units used in GM vehicles - the Super Turbine 300 (ST300 or 300THM) had a similar setup as well as Buick's 1955-1963 twin turbine Dynaflow.

By 1980, usage in GM passenger cars was on a decline because of the 1973 Arab Oil Embargo, when the Hydramatic 200-4R and 700R4 overdrives were phased in. The Presidential Limo (a modified 1984 Cadillac Fleetwood Brougham) used during the Reagan Administration was the last known passenger vehicle to use the THM400, alongside the C and K series (full size) Chevrolet/GMC pickups and G-series (full size) vans. Today, the U.S. Army HUMVEE is the only vehicle using the THM400. The civilian Hummer H1 originally had the 3L80s, but the current model has had a 4L80E since the mid-1990s.

Other non-GM firms have used the THM400 and its 4L80E successor, including Ferrari (in the 400, 400i and 412 models), Jeep (usually found in the SJ pickups and SUVs), Jaguar (found in their pre-1997 XJ6 and XJS coupes), Rolls-Royce (1968–1980 Silver Shadow), and AM General. It has been known to adapt a THM400 to other engines via the use of adapter plates. During the 1970s, there were more BOP (Buick/Oldsmobile/Pontiac/Cadillac) transmission cores produced for the THM-400, making other transmission cases a rare find. No THM400 was produced with multicase bell housings.

Turbo 400 transmissions are very popular in drag racing, monster truck racing and mud racing due to their great strength. Much of this strength comes from the use of a cast iron center support to suspended the transmission's concentric shafts that join the clutch assemblies to the gear train, and to provide a robust reaction point for first gear (the reaction carrier is tied to the center support through a roller clutch).

Also, the TH400 was the first three speed, Simpson-geared automatic to use overrunning clutches for 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, multiplate clutch to provide second gear reaction, the TH400 is able to withstand very high torque input. As a result, it met with considerable success in commercial vehicle applications.

For 1987 GM changed the nomenclature of their Turbo Hydramatic transmissions — the THM400 was renamed to the '3L80' (3 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 1992 a 4-speed overdrive version, the 4L80-E, 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 — almost all of the THM400/3L80/3L80HD's components are interchangeable.

THM350

In late 1967 the Chevrolet Motor Division introduced a lighter duty version of the THM400 for use in the 1968 Camaro — the THM350 (the numerical ID is relative to the torque capacity). Since the 1969 model year, this transmission succeeded the earlier two-speed automatics, and by the late 1970s when GM started using corporate powerplants, a universal bellhousing pattern was introduced (the THM350's predecessor, the Buick Super Turbine 300, had a multicase bellhousing to fit the Chevrolet inline six). It can be identified by the oil pan which is said to look like a square with a corner cut off.

Some would suggest that the THM350 (or Turbo 350 as called by drag racers and car enthusiasts) was based on the earlier Buick Super Turbine 300 - some components interchange between the two. Both Chevrolet and Buick divisions produced the THM350.

It has been rumored that the reason for the THM350's release after the TH400, is that although the THM350 had been in developement longer(disputable), it often failed under heavy torque or stress.

The Turbo Hydramatic 350 was also regarded as a 'three speed Powerglide' and during its development, was generally called this; Although it uses a torque converter shared with or based on the THM 400 and Buick Super Turbine type transmissions (sans variable pitch stator) it has a great family resemblance to the 1962-'73 Aluminum Powerglide from Chevrolet and was largely derived from the Chevrolet design. One important difference in the THM 350 compared to the THM 400 is there is no fixed center support midway through the geartrain, this important difference in layout permitted THM 350 to be adapted to the Corvair where the drive and driven ends are the same. This feature was not exploited but Corvair may have eventually used the THM 350 had it remained in production, and Chevrolet was experimenting with mid-engine Corvette designs that might also have used this advantage had they ultimately reached production. Air cooled versions (with a baffle on the torque converter and air intakes cast into the bellhousing) of the THM 350 appeared mid 1972 in Chevrolet Vega and Nova 6.

Around 1980 a lockup torque converter was introduced; this transmission was phased out in 1984 in GM passenger cars for the 700R4. Chevrolet/GMC trucks and vans used the THM350-C until 1986. The lockup torque converter was deemed unpopular with transmission builders - B&M Racing once marketed a conversion kit for THM350-Cs during the early 1980s until the advent of high-stall lockup torque converters when its overdrive counterpart (THM700R4/4L60) were modified. The standard TH350 is still very popular in drag racing.

A derivative, the THM250, was introduced in 1974 in Chevrolets as a Powerglide replacement. Internally, the THM250 is a THM350 without the intermediate clutch pack with a band adjuster similar to the Powerglide. It was later reintroduced in 1979 as the THM250-C in the wake of the failure-prone THM200/200C.

THM200

Right after the 1973 Arab Oil Embargo, GM developed a lighter-duty version of the THM350 with lightened materials - primarily alloys in place of ferrous materials (e.g. clutch drums and oil pump). The Turbo-Hydramatic 200 was born; however, this transmission was notorious for its failure rate when used behind a V8 motor - especially the Oldsmobile V8 350 Diesel.

1976 GM vehicles first saw use of the THM200 - from the GM T platform to GM X-Bodies (Chevrolet Nova et.al.).

Transmission shops nationwide, along with GM repair facilities, have swapped in THM350s since the 200s were failure prone. Starting with the 1979 model year, vehicles which had the THM200/200C as standard equipment were optioned with the THM250-C, actually a THM350 without the intermediate clutch pack along with an adjustable band similar to the Chevrolet Powerglide.

Around 1979, it received a lockup torque converter, and some internal components (primarily the low/reverse clutch drum and planetary gears) were later shared with the Turbo-Hydramatic 200-4R.

THM200/200Cs were produced until 1986.

200-4R

Around 1980, GM's Hydramatic division decided to incorporate an overdrive gear, and using the THM200 as a base, the Hydramatic 200-4R was born. Internally, the components which were prone to failure in the THM200 were improved, and this transmission was used with high-power applications - primarily the Buick Grand National. GMs powered with the Oldsmobile 5.7L Diesel powerplant were coupled with the 200-4R in place of the 200.

Unlike the 700R4, the 200-4R has a multicase bellhousing for use with Chevrolet and Buick/Olds/Pontiac/Cadillac (BOP) powerplants. Since the external dimensions are similar to the THM400/3L80, 200-4Rs are usually swapped in place of THM400s in older vehicles.

The THM200-4R was phased out after 1990 - its final usage was in the GM B-body lineup (Chevrolet Caprice, Oldsmobile Custom Cruiser station wagon, Cadillac Brougham) coupled to either a Chevrolet 305 or an Oldsmobile 307 engine. It is believed that a HD version of the 200-4R was used in the late 80s Caprice 9C1 police package using the internals from the Buick Grand National.

700R4 / 4L60

At approximately the same time as the 200-4R's release, the Hydramatic 700R4 was introduced 1982 for use in Chevrolet/GMC vehicles.

The gearing for the 700 is (commonly rounded off to 3.06, 1.63, 1.00, 0.70, and 2.29):

  • First - 3.059
  • Second - 1.625
  • Third - 1.000
  • Fourth - 0.696
  • Reverse - 2.294

Initially, the 700R4 was not considered a strong transmission, since the torque of a 350 in³ V8 would lead to transmission failure. The original version of the transmission had a 27 spline input shaft - this was but one of many possible and common failure points with the early transmission. However, the design was continually refined and upgraded, and in 1987, the 700 was used behind a 350 small block V8 (from IROC-Z Camaros to pickup trucks).

For 1984, 700R4s designed for use behind Chevrolet small block V8s received a 30 spline input shaft which used a different torque converter than its 2.8 V6 and 2.2 L4 powerplants. Between 1984 - 1987, internal components, from the ring gear to the oil pump housing, were updated, ending with the auxiliary valve body (for 700s manufactured after October 1986).

Without pictures, the 700 can be identified by the oilpan having a rectangular shape being longer front-to-rear than side-to-side and held to the transmission by 16 bolts, 3 bolts front, 3 bolts rear, 5 bolts left side, and 5 bolts right side.

The tailshaft housing is held onto the main case by 4 bolts (the bolt spacing is similar to the THM350), and uses a square-cut o-ring seal, and not a gasket. The typical width of this transmission where it bolts to the engine is 20 inches (510 mm) overall. From the engine/trans mating surface to the crossmember mount bolt is 22-1/2 inches (570 mm), and engine/trans surface to output shaft housing mating surface is 23-3/8 inches (594 mm) overall, with the tailshaft housing typically measuring 7-5/8 inches (194 mm).

Transmission fluid cooler lines: on the 700R4 the bottom fitting on the right side of the transmission is the "out" line to the cooler and the top fitting is for the return line from the cooler. These fittings are 1/4-inch pipe thread, and CAN include an adapter from the factory for threaded steel lines in an SAE size. 4L60Es manufactured after 1995 use the modern-day snap-in connections as opposed to threaded SAE fittings.

4L60

The 700 was renamed the 4L60, when the electronic version, 4L60-E, was phased in (1993 for GM trucks, vans, and SUVs, and 1994 for RWD passenger cars). Around 1996, a bolt-on bellhousing was phased in (along with a six-bolt tailhousing) when the transmission was bolted behind an inline four cylinder or the Vortec engine family.

Applications:

4L65-E

An updated 4L60-E, the 4L65-E, was phased in around the 2003 model year when coupled behind the 6.0 Vortec. Five-pinion planetaries, along with a modified drum/input shaft assembly, were improved to withstand the 300+ ft·lbf (over 400 N·m) of torque.

External links