By on May 12, 2022

Our Abandoned History coverage of the Turbo-Hydramatic transmission series continues today. The THM was a singular solution to two different automatic transmissions in use by Oldsmobile, Cadillac, and Buick in 1963. Turbo-Hydramatic arrived at a time of modernization for the automatic, which prior to the mid-Sixties was regarded as inefficient and less than smooth.

The THM400 was the 1964 replacement for the Hydra-Matic and Buick’s Dynaflow and established itself as a smooth and reliable gearbox. It proved useful in a variety of luxury and heavy-duty applications and shrugged off weight and torque easily. In short order, it took off as the transmission of choice for various small manufacturers outside of GM. However, no matter how excellent the THM400 was, it found itself squeezed by a drive toward greater fuel efficiency. It was also a bit hefty to be of broad use in smaller or lighter passenger cars. GM needed more Turbo-Hydramatics!

It wasn’t too long before the Turbo-Hydramatic line expanded. In 1969 a new version appeared, the THM350. The three-speed was developed specifically to take over for two older GM gearboxes. First was the Super Turbine 300, a two-speed that was found in Buick, Pontiac, and Oldsmobile models from 1964 to 1969. Each company had its own marketing name, but the Super Turbine underneath was always the same.

The THM350 also replaced the Powerglide, another two-speed automatic. Found primarily on Chevrolet vehicles, the Powerglide continued life for a few more years after it ceded most of its duties to the 350. It remained in production through 1973. Even though the new 350 wore fancy Turbo-Hydramatic branding, it was actually developed by the engineers devoted to Powerglide. The THM350 was often considered a three-speed Powerglide among those in the know, and the team who worked on it internally at GM used that name too.

The THM350 used the same torque converter as the heavier THM400, though it skipped the Switch-Pitch stator we learned about last time. Other than its converter, it worked more like the Powerglide. It appeared during the 1969 model year across GM’s lineup and replaced the aforementioned Powerglide and Super Turbine 300. A notable development on the THM350 appeared during the 1972 model year when an air-cooled version arrived. The air-cooled variant was used on the smaller Chevrolet Vega and Nova.

THM350 found its way into early Seventies GM trucks as well and was mated to four-wheel drive as necessary. For four-wheel-drive, the transmission used an adapter made of iron that attached it directly to the transfer case, just like the THM400. Some examples of heavy-duty versions of the THM350 were confusingly called THM375-B.

A further development of the 350 arrived late in the 1979 model year, in the form of a new lock-up torque converter. That version was branded as THM350-C and was the final development of the THM350. It remained in production through 1984 for passenger cars (phased out in favor of the 700R4) and lived on in various GM trucks and vans through 1986.

There was an interesting product practice at two of GM’s divisions with regard to transmissions in the late Sixties: Buick and Chevrolet both restricted transmission choice. Two-speed Powerglides were provided with most full-size vehicles at Chevrolet and Buick lots if they had a smaller engine. If a customer wanted to enjoy the benefit of the new Powerglide-esque THM350 and its three speeds, they’d need to purchase a larger V8. This was in contrast to Pontiac and Oldsmobile (who offered nearly identical cars, of course), as they paired the three-speed with any engine available.

The second development of the THM400 was ready for the 1971 model year. Dubbed the THM375, the lower number was an indicator of its status just under the 400. It was mechanically very similar to the THM400 but intended for lighter duty. The 375 used a smaller set of shafts and yoke and had one less friction plate in the clutch packs. It used the THM400’s bolt pattern but had a longer output shaft.

GM’s lesser full-size models were the beneficiary of the THM375 when they were redesigned for 1971. Both the fourth-generation Buick LeSabre and seventh-generation Oldsmobile 88 received the 375, paired most often to the stalwart Buick 350 (5.7-liter) V8. The 375 was rather short-lived and existed only through 1976.

In other parts of Chevrolet’s lineup where the 375 or 400 were not in use, models still used the Powerglide through 1973. In 1974 that two-speed was finally and fully replaced by THM, with the introduction of the 250. The new THM250 was a derivative of the 350 and essentially continued on in the Powerglide engineering tradition. The primary difference between the 350 and 250 was the removal of the intermediate clutch pack. A lighter-duty transmission, it was typically used with smaller engines. It was never paired to any engine larger than an inline-six, found in the Nova and Camaro for 1974-1975.

THM250 also proved a very short-lived gearbox and was replaced after just three years by the THM200. The 200 was meant for even less power than the 250 and arrived in 1976. Keep the 250 in mind though, we’ll return to that in a moment. The THM200 arrived shortly after the 1973 oil crisis, when efficiency was suddenly the top consideration of every single automaker around the globe. The 200 was again a derivative of the THM350 but had an emphasis on the use of lighter materials. Aluminum alloys were used on internal components, instead of heavier metals.

For 1976 the 200 was implemented on the new T-body platform in the Chevette and similar. The Chevette needs some Rare Rides Icons coverage, as the T platform underneath it was truly global and important. The 200 also found its way into the aged X-body cars like the Chevrolet Nova and Oldsmobile Omega. It was even used in a truck, Chevrolet’s captive import LUV, and in the truck’s true identity as the Isuzu P’up.

Even though it was a light-duty transmission, that didn’t stop GM from using it in larger and more powerful cars than the Chevette. For example, the 200 was used with Oldsmobile’s terrible 5.7-liter diesel, among other applications in GM’s 60-degree V6, the 2.3-liter Vega 4, and with the Isuzu 1.4 in the Chevette. It was used in cars as large as the full-size Caprice.

It turned out the THM200 wasn’t exactly reliable, doubly so when used in heavier and more powerful cars. When it was responsible for shifting a V8 Caprice around all day, the 200 didn’t prove to have great longevity. Mechanical and hydraulic issues were both common and lead to premature transmission failure.

Issues with the 200 were prevalent enough to lead to a class-action lawsuit. GM maintained its innocence and said that the 200 was a family of transmissions and not just one. It was a valid claim if one considers various bellhousings to be different transmissions altogether. The suit was filed against GM in March 1979 but wasn’t settled until 1986. GM decided to settle and put $17 million in escrow to cover repairs, with an additional $2.5 million in cash reserves in case there were more claims than anticipated. Repairs at the time were pegged at $500 a pop ($1,318 adj.)

THM200 was so bad that GM offered a bit of an out, and for the 1979 model year offered the previously discontinued THM250-C as an option in place of the THM200. The 200 was turned into the THM200-C for 1979 with a lock-up converter like the rest of the line. It continued in production until 1987.

Let’s step back to THM400 for a moment. As GM had various other Turbo-Hydramatic transmissions in use, the chunky old 400 was phased out of passenger cars around 1980, in favor of the lighter and more efficient units outlined above. It continued in use in GM’s full-size C/K trucks line, as well as G-series vans like the G10 and Vandura. It remained in that usage through the 1990 model year, by which point it had been renamed to 3L80.

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

By the early-mid Eighties, it was evident that vehicles needed another forward gear to cope with the pressures of fuel economy and greater performance. That’s where we’ll pick up next time, as the Turbo-Hydramatic line entered the brave new world: Fourth gear.

[Images: GM]

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29 Comments on “Abandoned History: General Motors’ Turbo-Hydramatic Transmissions (Part II)...”

  • avatar

    Imagine GM installing an undersized transmission in a car that failed prematurely – then denying there was ever a problem…

    • 0 avatar

      Not much has changed to current day. Now they are denying that the 8 speed RWD based transmission as installed in the Camaro, pickups and SUV’s was a faulty design from the start and now have another law suite upcoming. The more things change the more……

      • 0 avatar

        Is that the one co-developed with Ford?

        • 0 avatar

          No, that’s the newer 10 speed. Not without problems of it’s own, Ford’s facing a class action lawsuit concerning how they perform (or lack thereof) in their F150’s from 2017 onwards. GM apparently has better programming or something as for whatever reason they have far fewer issues, at least enough so that nobody’s suing them yet.

  • avatar

    This is where blatant cost cutting takes you to.
    No one argues how reliable the THM400 and (to a lesser degree) THM350 were.

    But no one talks about the THM200 nor 250.

    • 0 avatar

      no joke… my parents 84 Olds 88 307 ate 3 of those stupid 200s, it had other issues, but the transmission was it’s achillies heel. their 76 Chevelle’s TH350 out lasted that 200, and only died from lack of fluid from a bad vacuum modulator.

      28 years later and 300,000 miles on it after the 1994 rebuild, that same TH350 is still going strong in a 77 Chevelle.

      • 0 avatar

        Yes a relative had the Pontiac Bonneville which had the small V8 and the 200 transmission. When it failed a second time he sold the car and he wasn’t a hard driver by any stretch of the imagination. Indeed it was a malaise era barge with wheezy horsepower at best. The replacement car was a 280 zx which had zero issues and convinced yet another person never to go GM again

  • avatar
    Mike Beranek

    The Cortez Silver LeSabre at the top of the article is giving me chills. Now THAT is an automobile.

  • avatar
    Bill Wade

    The Buick Grand National had the THM200. I had three of them and abused the cars to death at the dragstrip with no failures. These were all mid 11 second cars after a bit of massaging.

    Your article implies it was extremely weak. Obviously there was a difference in the ones used in the GN if that’s the case.

    It would be interesting to know what they were.

  • avatar

    It’s tough to imagine a bad 3-speed auto, but leave to GM (or Peugeot or something), but is the C6 and 727 Torque Flight headed for equal love (as the TH400)? Or the FMX, C4 and others?

    Of course big (truck) 3-speed Transmissions were overbuilt when used in passenger cars (normally with big V8s), usually with no others available. They ran a range from passenger cars to medium-duty commercial trucks, but it seems like more if a cost cutting scenario.

    Big Buicks and such were typically used for towing travel-trailers anyway, probably more so than pickups (that weren’t too good at hauling the family plus dogs).

    • 0 avatar
      Art Vandelay

      Not that FMX. That thing is stupid heavy for how strong it isn’t compared to a C6.

      I think the big 3’s main 3 speeds were all good. The AOD can get tossed off a cliff though unless you build the heck out of it.

      • 0 avatar

        Did Ford make decent OD trans in the ‘80s? The AXOD (Taurus/WindStar/Conti) was tragic and should’ve been recalled. The rest went slightly uphill from there. The E4OD (C6 replacement) didn’t get sorted (sort of) until ‘98.

  • avatar

    You are becoming the new Ate Up with Motor. Where did he go? Those articles he posted were the best researched I had read not from internal memo. These are also outstanding. Meticulous and well wrritten.

  • avatar
    Arthur Dailey

    The picture/ad for the 1975 Chev Caprice Classic Coupe took me back. I had one, cream paint with a bordello deep red interior and vinyl half roof. Being a wastrel mine had the 454 engine. Which if I remember correctly was paired with the THM400? Horsepower was off course ‘strangled’ by the required pollution controls. But torque was good. The powertrain never had an issue. The instrument panel was an ergonomic nightmare, with the requisite ‘tick’ in indicator on the speedometer. Overall deserving of the reputation as a ‘highway queen’.

    • 0 avatar

      What caused the erratic display of the speed on the sweep speedometers? On the “Rare Classic Cars” YouTube channel, all of Adam’s old GMs and Fords with the sweep speedometers are almost unfailingly rock-steady, but my Mom and I both had Olds Cutlasses in the 1978-1980 MY range where the speedometers would “boing-boing-boing-boing” anywhere from 15mph-30mph or so. (The worst one I ever saw was in a 1978 Regal, where the speedo would bounce up 20mph and back, complete with a “thunk” that was audible from the back seat!) I presume it’s something in the pickup on the transmission, if not something wonky in the cable itself.

      To the point of your Chevy, which must have been a looker, I’ve seen a dealer training film on YouTube where someone is actually trying to manually shift the transmission in a Caprice or Impala, and during the shift itself, the speedometer drops out, then displays the speed again after a second!

      Didn’t ride in as many Fords or Chryslers of the era, but the ones I recall didn’t have the issue, specifically my great-Aunt’s 1977 LTD! (What a huge, beautiful boat that was!)

      • 0 avatar
        Arthur Dailey

        I don’t know the root cause of that problem with GM speedometers of that era. Perhaps the length of the ‘sweep’ required? I used to use taxis quite often then and I cannot remember one GM taxi with those ‘long’ speedometers that didn’t have that issue.

        • 0 avatar


          And recall that the Regal I mentioned didn’t get a sweep soeedo until 1984; from 1978-1983, the fuel gauge, square speedo, and a third gauge which had an optional analog (and quartz in the 1983s, at least) clock, with a strip of warning lights to the right.

          Come to think of it, not every Cutlass of the era had the issue, having ridden in several of them—they were the best-selling cars back then! And my 1978 Cutlass wasn’t as bouncy as my Mom’s 1980.

      • 0 avatar
        Jeff S

        @sgeffe–Have you seen Rare Classic Cars latest 3 part series on Adam’s 75 Olds Royale Coupe and a 76 Olds 98 Regency?

  • avatar
    j lu

    Very interesting article about GM’s transmissions. I can relate to the THM 200 woes.
    I worked for a state regulatory agency and we had just taken over a land title company going into default. I began to use one of the company cars while acting as conservator, a 1977 Caprice Coupe with relatively low miles, about 27K. I noticed right away that shifts were sloppy and at times, delayed along with slippage. The situation was getting worse and I attributed the transmission woes to perhaps prior rough use. That is until I got it into the transmission shop where the owner gave me the complete run down on how bad a transmission this was, by design. He was seeing many of these transmissions coming in with premature failures.
    He said this was a clear cost cut move on the part of GM and told me they never should have placed such a weak, fragile transmission in a large vehicle. He rebuilt it with as many heavy duty parts as he could manage and it did shift beautifully after the rebuild. The car was sold as part of the liquidation of that land title company’s assets. I wonder how long it lasted?
    I love how GM claims ignorance when they know what they did. Always greed and the almighty dollar that drives these changes and they could care less. Much like Ford with the Pinto gas tank. Company documents revealed that their engineers wanted to install a shield to protect the tank at a manufacturing cost of less than $2 but the bean counters (actuaries) calculated that the shield cost vs any law suits filed and determined that the law suit costs would be less. Never mind the burned bodies, just mind the dollars. Ah, capitalism.
    But I digress, great article.

  • avatar

    I had a 79 Malibu with a 305 V8 and the TMH 200. I started hearing reports of how junk the transmission was so I traded the car in with just 50,000 miles. I decided not to wait and see if major transmission trouble would hit or not.

  • avatar

    Ah, the infamous THM200. My mom bought a brand new ’78 Chevy Malibu Classic 4-door in late December, 1977, replacing our ’66 Rambler American 440 4-door (232 2-bbl with Borg-Warner automatic, factory air). The Malibu was equipped with the 305 2-bbl and THM200, plus a/c. Two-tone blue metallic, it was full Disco Era.

    Less than a year after she bought it (she rode the bus to work, and hardly drove the Malibu), the THM started screwing up, with jerky 1-2 upshifts, and lazy, flare-ridden 2-3 upshifts. It was in and out of the dealer’s shop for the next several years, for fluid changes and minor tweaks. The dealer told her that it needed annual fluid and filter changes (huh?).

    Finally, in ’85, I was driving it to DFW Airport, to pick her up (her first grandson had been born, in California), when suddenly it wouldn’t go into third, unless I backed completely off the throttle. The (aluminum) internal case support had broken, a common failure.

    The fix was a swap to a rebuilt THM350, performed by a local shop. That required a new rear mount, moving the crossmember (it was bolted to the frame), adding a throttle kickdown cable and linkage part on the carb to attach it, a vacuum line to the modulator, and a revised driveshaft. All told, it was under $600, and solved all the problems. Oh, and she did get $500 from GM under the class action. It had tons of other recalls, from the c-clip axle shafts in the rear end (the “button” on the end of the shafts could break off, causing the wheel, drum and axle shaft to slide out), to the a/c condenser failures.

    We sold that car after she passed away in 2012, and it had only 72,000 miles put on it, in nearly 35 years.

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