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Turbo-Hydramatic
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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 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.
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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 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, sometimes 2), 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 Cadillac division in the late 1930s, the two transmissions were not mechanically related.
Super Turbine 400 / THM400 / 3L80 / 3L80HD / 4L80E
The THM400 (or the Turbo 400, which it is called by drag racers and car enthusiasts) is a 3 speed automatic transmission that was first introduced at the beginning of 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 THM400s 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 THM400.
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 GM 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 400/412), Jeep (usually found in the SJ pickups and SUVs), Jaguar (found in their pre-1997 XJ12 and XJ-S coupes), Rolls-Royce (1965–1980 Silver Shadow and 1980-1992 Silver Spirit series cars, along with their Bentley stablemates), 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.
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 roller clutch whose 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.
Also, the THM400 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 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.
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 1991 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.
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. The case is tapped for either self-sealing 1/4"NPT fittings, or 1/2"UNF fittings with a washer seal. 5/16" or 3/8" rigid coolant lines are generally connected via appropriate double-flared adapters.
Gear Ratios are:
- First Gear - 2.48 to 1.00
- Second Gear - 1.48 to 1.00
- Third Gear - 1.00 to 1.00
- Reverse - 2.07 to 1.00
THM350
The Turbo Hydra-matic 350 was first used in 1969 model cars. It was developed jointly by Buick and Chevrolet to replace the two-speed Super Turbine 300 and aluminium-case Powerglide transmissions. So, although it carries the Turbo Hydra-matic name, the Hydra-matic Division of General Motors had little, if anything, to do with its design. The 350 and its 250, 250c, 350c and 375b derivatives have been manufactured by Buick in its Flint, Michigan, plant and by Chevrolet in Toledo and Parma, Ohio, and Windsor, Ontario.
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 development 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.
The gearing for the 200C is:
- First - 2.74:1
- Second - 1.57:1
- Third - 1.00:1
- Reverse - 2.07:1
200-4R
In 1980, for 1981 models, 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 THM-350, 200-4Rs are usually swapped in place of THM-350s in older vehicles to provide an overdrive gear.
Early models had PRND321 on the cluster, while later models had PRNDD21, with the left D identified as the overdrive gear by a square or oval ring.
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 an 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 / 4L60E / 4L65E
The Hydramatic 700R4 was introduced in 1982 for use in Chevrolet/GMC vehicles.
In 1990 the 700R4 was renamed the 4L60.
1992 was the last year of wide spread usage of the 700R4 (4L60).
1993 Camaro, Corvette & Typhoon were equipped with the last production 700R4's, also the last design change of the 700R4 with an added checkball to the valve body.
In 1992 electronic controls were added and it became the 4L60-E. The 4L60E went into service in trucks, vans, and SUVs in 1993 (for the record, some HD trucks had the 4L60) and in all RWD passenger cars (Vette, F and B/D bodies) in 1994.
In 2001 an updated version, the 4L65-E, was introduced. Five-pinion planetaries, along with a strength-improved output shaft, were improved to withstand the 300+ ft·lbf (over 400 N·m) of torque of the 6.0 Vortec engine.
700R4 / 4L60 / 4L60E / 4L65E Technical Description
The 700R4 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 a SAE size. 4L60Es manufactured after 1995 use the modern-day snap-in connections as opposed to threaded SAE fittings.
The original version of the transmission had a 27 spline input shaft which was a common failure point. In 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).
In 1995 the 4L60E received a PWM-controlled lockup converter.
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.
The gearing for the 700 is:
- First - 3.059
- Second - 1.625
- Third - 1.000
- Fourth - 0.696
- Reverse - 2.294
(commonly rounded off to 3.06, 1.63, 1.00, 0.70, and 2.29).
700R4 / 4L60 / 4L60E / 4L65E Applications
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