Editing Turbo-Hydramatic (section)

==THM200==
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[[File:Ypsilanti Automotive Heritage Museum May 2015 059 (1975-87 THM 200 transmission).jpg|thumb|A THM 200 transmission, produced between 1975 and 1987]]

After the 1973 [[1973 oil crisis|OPEC 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. The THM-200 was first used in 1976 models including GM's [[GM T platform (RWD)|T-cars]] (which includes the rebadged [[Isuzu Gemini]] sold through Buick dealers as the Buick/Opel by Isuzu), [[GM X platform (1962)|X-cars]], and some Isuzu automobiles (Chevrolet LUV and Isuzu P'up). However, this transmission was notorious for its failure rate{{citation needed|date=May 2020}} when used behind any engine - the largest being the Oldsmobile 5.7&nbsp;L diesel. Multicase bellhousings were used - bellhousing patterns included Chevrolet V8, Buick-Oldsmobile-Pontiac, [[Chevrolet 2300 engine|Vega 4]], GM 60 degree pattern (includes the Tech IV), and [[List of Isuzu engines#Isuzu G engine|Isuzu G engine]].

It was GM's first transmission which used a throttle valve cable (similar in design to the Chrysler Torqueflite part throttle kickdown linkage) controlling the shift points and part throttle kickdown. This setup was later incorporated into the THM700R4.

Because the THM-200 shared external dimensions and output shaft size and spline count with the THM-350, the THM-350 was often used to replace the weaker, less reliable THM-200 and THM-250C. The only thing which had to be added was a vacuum line to the vacuum modulator on the THM-350.

Starting with the 1979 model year, vehicles which had the THM-200/200C as standard equipment were optioned with the THM250-C, which is a THM-350 without the intermediate clutch pack along with an adjustable band similar to the Chevrolet Powerglide. Also in the 1980 model year, the THM-200 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. The low/reverse sprag (roller clutch) assembly was also shared with the 1988-04 Chrysler Torqueflite 904 (also 30, 31, 32RH) and its derivatives e.g. the A500 and 42RE. THM200/200Cs were produced until 1987.

{| class=wikitable
|+Gear ratios
!Gear
!Ratio
|-
|1||2.74:1
|-
|2||1.57:1
|-
|3||1.00:1
|-
|R||2.07:1
|}

===THM200-4R===
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The 200-4R was introduced for the 1981 model year. Some components{{vague|date=February 2024}}{{which|date=February 2024}} which were prone to failure in the THM200 were improved, and in the later 1980s, this transmission was used with high-power applications — primarily the Buick Grand National and the 1989 Pontiac Firebird Trans Am Indy 500 Pace cars. The 200-4R was configured with several different torque converters depending on the vehicle application.

However, this transmission was also prone to failure (especially in D-body Cadillacs) and received improvements during its production run. The first improvement came in 1984 with a change of a servo piston from using split Teflon sealing rings to a servo using lip seals. A real problem area was the stamped-steel drive shell, which would strip out, losing reverse. With the 1985 production run, GM started installing a hardened drive shell, but continued to supply the original style until parts inventories were exhausted. Another major problem area was the pump assembly. The pump halves were made of cast aluminum and the pumps themselves were made of made up of steel segments like a power steering pump. There was a steel hub and variable ratio outer ring. Because the pump segments traveled in an eccentric circle, guide rings were necessary on top and bottom of the center hub. These rings would break and cause the pump to stop pumping, as well as damaging the aluminum housings. Aftermarket hardened rings solved this problem.

Unlike the 700R4, most 200-4Rs have a multicase bellhousing for use with Chevrolet, Buick/Olds/Pontiac (BOP), and Cadillac engines. However, 200-4Rs share mounting locations with the TH-400. Since the external dimensions are longer than the TH-350 but the drive shaft yoke spline count/diameter was the same, the 200-4Rs can be swapped in place of TH-350s, with the shortening of the drive shaft, in older vehicles to provide an overdrive gear. Early models{{vague|date=February 2024}} had a '''{{nowrap|P&nbsp; R N D 3 2 1}}''' quadrant, while later models{{which|date=February 2024}} used '''{{nowrap|P  R N {{not a typo|🄳}} 3 2 1}}'''.

The THM200-4R can be found in the following vehicles:

* 1981–90 [[GM B platform|B-bodies]]
* 1981–84 [[GM C platform (RWD)|C-bodies]]
* 1983–88 [[GM G platform (RWD)|G-bodies]]
* 1985–90 [[GM D platform|D-bodies]]
* 1989 [[Pontiac Firebird Trans Am]] Indy Pace car (with the [[Buick_V6_engine#LD5|turbocharged LD5 Buick V6]] and a turbocharger)

The THM200-4R was phased out after 1990; its final usage was in the [[GM B platform|GM B-body]] vehicles.{{CN|date=February 2024}}

{| class=wikitable
|+Gear ratios
!Gear
!Ratio
|-
|1||2.74:1
|-
|2||1.57:1
|-
|3||1.00:1
|-
|4||0.67:1
|-
|R||2.07:1
|}
{{anchor|700R4|4L60|4L60E|4L65E|4L70E}}