General Motors THM200 / THM-200C

General Motors' light three-speed automatic — in the Chevrolet S-10 and GMC Sonoma.

It is the TH350's smaller replacement and it earned a poor reputation for exactly that reason: GM built it lighter to save weight and fuel, and it went behind engines that overwhelmed it. A THM200 that failed early was usually asked to do a TH350's job.

Three ratios and no overdrive is the design, not a missing gear — and on a truck geared for load that is the commonest complaint about one.

Its faults are the governor and the vacuum modulator, both mechanical parts that drift with age and produce changes arriving at the wrong road speed, consistently rather than intermittently. That is a very different symptom from slipping and a far cheaper repair; the modulator can be tested with a hand pump in minutes.

The 200-4R that shares its name is a different, much stronger four-speed, and a parts listing conflating the two will be wrong about everything.