Turbo-hydraulic transmissions General Motors (part II)

Our abandoned story coverage the Turbo-Hydramatic transmission series continues today. THM was the only solution for two different automatic transmissions used by Oldsmobile, Cadillac and Buick in 1963. Turbo-Hydramatic came during the upgrade of the automatic transmission, which until the mid-sixties was considered inefficient and less than smooth.

The THM400 was in 1964 a replacement for the Hydra-Matic and Dynaflow from Buick and has proven itself as a sleek and reliable gearbox. It has proven useful in a variety of luxurious and heavy applications and easily reduced weight and torque. It soon became the transmission choice for various small manufacturers outside of GM. However, no matter how great the THM400 was, it proved to be a crushed drive for greater fuel efficiency. It was also a bit hefty to be widely used in smaller or lighter cars. GM needs more Turbo-Hydramatics!

It wasn’t long before the Turbo-Hydramatic line expanded. In 1969, a new version of the THM350 appeared. The three-speed was designed specifically for GM’s two old gearboxes. First there was the Super Turbine 300, a two-speed that was found in the Buick, Pontiac and Oldsmobile models from 1964 to 1969. Each company had its own marketing name, but Super Turbine under it has always been the same.

The THM350 also replaced the Powerglide, another two-speed automatic. Found mostly on Chevrolet cars, the Powerglide continued to live for several more years after handing over most of its 350 duties. It remained in production until 1973. Although the new 350 had the fashion brand Turbo-Hydramatic, it was designed by engineers dedicated to Powerglide. The THM350 was often considered a three-speed Powerglide among those who know, and the team that worked on it inside GM also used that name.

The THM350 used the same torque converter as the heavier THM400, although it missed the stator switching pitch we learned about last time. Aside from its converter, it worked more like a Powerglide. It appeared in the 1969 model year in the GM line and replaced the aforementioned Powerglide and Super Turbine 300. The notable development of the THM350 appeared in the 1972 model year, when the air-cooled version appeared. The air-cooled option was used on the smaller Chevrolet Vega and Nova.

The THM350 also hit GM trucks in the early 1970s and was paired with all-wheel drive when needed. For all-wheel drive, the transmission used an iron adapter that mounted it directly to the transfer case, like the THM400. Some examples of heavy-duty versions of the THM350 have been confusedly called the THM375-B.

Further development of the 350 appeared in the late 1979 model year as a new torque converter with lock. This version was labeled as THM350-C and was the final development of THM350. It remained in production until 1984 for passenger cars (gradually discontinued in favor of the 700R4) and lived in various GM trucks and vans until 1986.

In the late 1960s, two divisions of GM had an interesting practice regarding transmissions: Buick and Chevrolet limited the choice of transmissions. Two-speed Powerglides were provided to most full-size cars on the Chevrolet and Buick lots when they had a smaller engine. If the customer wanted to enjoy the benefits of the new Powerglide-style THM350 and its three speeds, he would need to purchase a larger V8. This was unlike the Pontiac and Oldsmobile (which of course offered almost identical cars) as they combined a three-speed car with any available engine.

The second development of the THM400 was ready by the 1971 model year. Named the THM375, the lower number was an indication of its status of just under 400. It was mechanically very similar to the THM400, but designed for lighter duties. The 375 used a smaller set of shafts and a yoke and had one friction plate less in the clutch packs. It used the THM400 spinning circuit, but had a longer output shaft.

Smaller full-size GM models were the beneficiaries of the THM375 when they were redesigned in 1971. Both the fourth-generation Buick LeSabre and the seventh-generation Oldsmobile 88 received a 375, most often paired with a durable 350-liter Buick (V5). . 375 was quite short-lived and lasted only until 1976.

In other parts of the Chevrolet line, where the 375 or 400 were not used, the models still used the Powerglide until 1973. In 1974, this two-speed was finally and completely replaced by THM with the introduction of 250. The new THM250 was derived from 350 and essentially continued in the Powerglide engineering tradition. The main difference between the 350 and 250 was the removal of the intermediate clutch package. A lower load transmission, it was commonly used with smaller engines. It was never combined with an engine larger than the native six found in the Nova and Camaro in 1974-1975.

The THM250 also proved to be a very short-lived gearbox and was replaced just three years later by the THM200. The 200 was designed for even less power than the 250, and appeared in 1976. However keep in mind 250, we’ll get back to that in a moment. The THM200 emerged shortly after the 1973 oil crisis, when efficiency suddenly became a major issue for every automaker worldwide. The 200 was again derived from the THM350, but emphasis was placed on the use of lighter materials. Aluminum alloys were used on the internal components, not heavier metals.

In 1976, the 200 was implemented on Chevette’s new T-body platform and the like. Chevette needs lighting for rare amusement badges because the T platform below it was truly global and important. The 200 also hit obsolete X-body cars such as the Chevrolet Nova and Oldsmobile Omega. It was even used in a truck imported by Chevrolet LUV, and in the true identity of the truck as the Isuzu P’up.

Although it was a light transmission, it didn’t stop GM from using it in bigger and more powerful cars than the Chevette. For example, 200 was used with the scary Oldsmobile 5.7-liter diesel, among other applications in the 60-degree V6 from GM, the 2.3-liter Vega 4 and the Isuzu 1.4 in the Chevette. It has been used in such large cars as the full-size Caprice.

It turned out that the THM200 is not very reliable, twice as much when used in heavier and more powerful cars. When he was responsible for shifting the V8 Caprice throughout the day, the 200 didn’t prove to be a great longevity. Mechanical and hydraulic problems were common and led to premature transmission failure.

Problems with 200 were common enough to lead to class action. GM claimed its innocence and said the 200 was a family of transmissions, not one. This was a valid claim when considered different bell tower be completely different gears. The lawsuit was filed against GM in March 1979, but was not settled until 1986. GM has decided to settle and put $ 17 million in deposit to cover the repairs, as well as an additional $ 2.5 million in cash reserves in case the claims are more than expected. Repairs at the time were tied to $ 500 apiece ($ 1,318, corrected).

The THM200 was so bad that GM offered a bit of an exit, and for the 1979 model year it offered to previously discontinue the THM250-C as an option instead of the THM200. The 200 was converted to THM200-C in 1979 with a lock transducer, like the rest of the line. It continued to be produced until 1987.

Let’s go back for a moment to the THM400. Because GM used a variety of other Turbo-Hydramatic transmissions, the stocky old 400 was taken out of passenger cars around 1980 in favor of the lighter and more efficient units described above. It continued to be used in GM’s full-size C / K truck line, as well as in G-Series vans such as the G10 and Vandura. It remained in such use until the 1990 model year, by which time it had been renamed the 3L80.

The name denoted three forward speeds, longitudinal position and a high strength rating of 80, which was invented by GM. GM renamed the entire THM line in 1987 to a new methodology and moved away from Turbo-Hydramatic names.

By the early to mid-1980s, it became clear that cars needed another gear forward to cope with the pressure of fuel economy and greater performance. This is where we will deal next time, as the Turbo-Hydramatic line has entered a wonderful new world: the fourth gear.

[Images: GM]

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