Tag: GM TH-200-4R Overdrive Transmission

What you need to know before buying a GM TH-200-4R Overdrive Transmission – Jim O’Clair @Hemmings

What you need to know before buying a GM TH-200-4R Overdrive Transmission – Jim O’Clair @Hemmings

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The overdrive four-speed automatic is replacement for older three-speed Turbo Hydra-Matics or two-speed Powerglides

Many classic cars that used an original Powerglide two-speed or TH-350 three-speed can benefit from installing a TH-200-4R four-speed automatic without having to perform major modifications. The 200-4R can be used on many other GM passenger cars because it was manufactured with both a Chevrolet and a B-O-P bellhousing bolt pattern. The taller, fourth gear allows the engine it is installed behind to rotate at lower RPM than a three-speed transmission, and this not only will save on gas and engine wear, but it also allows you to change to larger rear axle ratios without severely impacting streetability.

TH-200-4R transmissions are very easy to locate from salvage yards, and most replacement parts are still available from transmission parts suppliers and auto parts stores. Heavy-duty parts for racing applications are available from transmission parts suppliers, as well.

Will a TH-200-4R fit in my car?

Your engine size should be a consideration; many muscle-car enthusiasts recommend using the TH-700-R4 or 4L80E overdrive units on large V-8 and higher performance engines. However, in many V-6 and small V-8 applications, a TH-200-4R will fit with fewer modifications.

The TH-200-4R, like the TH-350, uses a 27-spline output shaft, which is similar in length to the TH-350 and the TH-200, making it a natural for many overdrive conversions. The TH-200-4R is also similar in length to the Powerglide and the B-O-P Super-Turbine 300 (two-speed), which makes it a popular unit for converting from a two-speed to a four-speed automatic.

The TH-200-4R has a 2.74:1 first gear ratio, and overdrive is 0.67:1. Its odd-shaped 16-bolt pan has 13mm bolt heads. The TH-200-4R was used in GM rear-wheel-drive cars equipped with the 231 Buick, 301 Pontiac, and the Oldsmobile 307, 350 gas and 350 diesel engines from 1981-’90; however, many Chevrolet 267 and 305 V-8s also used the TH-200-4R because of the multi-fit bellhousing.

The transmission identification is on a plate on the right side of the case towards the tailshaft. This ID plate is attached by one rivet. The plate will have a two- or three-letter transmission code in large letters.

Which TH-200-4R should I get?

The most desirable TH-200-4Rs for performance enthusiasts are the units manufactured for Buick Grand National, Olds 4-4-2 and Chevy Monte Carlo SS in 1986-’87. These units used a special valve body. They also had a larger reverse boost valve, second to third intermediate servo, and a specially designed governor assembly. Their BQ, OZ, CZF, KZF or BRF transmission codes can identify these more desirable units.

This transmission is ideal for swapping with a TH-350 or a Powerglide, because the overall length and the bell housing bolt pattern of the TH-200-4R are the same, and your original driveshaft does not have to be shortened. The output shaft is 27-spline, the same as the TH-350’s. Moving the crossmember will be necessary, because the TH-200-4R crossmember is mounted on the extreme end of the tailshaft.

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