Article Errors

Asked by Dec 08, 2012 at 06:20 PM about the 1958 Pontiac Bonneville

Question type: General

First, GM never made a hartop covertible.  It came as a soft top convertible and two door coupe in 1958.  Also, the hydromatic was a three speed with standard torque converter.  Pontiac didn't have a 4 speed automatic until the 1980s.

3 Answers


Thanks... What article are you referring to?

True. Pontiac's only came with soft tops on convertibles. Only the 1957 through 1959 fords had the hardtop convertibles.The hydromatic in the 58 pontiac is a 4 speed automatic. It does not have a torque converter per se. It has a fluid coupling. The only time that pontiac had a torque converter was in 1953 when the hydromatic plant burnt down. The pontiacs were fitted with the chevy power glide transmission for 3 months only. All gm cars except chevy and buick had the 4 speed hydromatic transmission. The last hydromatics were installed in the 64 pontiac bonneville and starchief and the cadillacs. In1965 the turbo 400 transmission took the hydro's place.


As a former '64 Cadillac owner I can confirm that the turbo 400 was available in 1963 mated to the venerable 390 engine and was standard in the 1964 Cadillac mated to the awesome 429 which was basically a reworked Corvette 427. Some are confused by the GM 4 speed hydomatic transmission's. These transmissions didn't have overdrive. First gear was really two gears. They started out in a compound low with a involuntary shift to low range followed by a hydraulic gear change to second gear with a clutch pack gear change to 1 to 1 high gear. GM made a mini version without the compound low gear called the Roto 5. These transmissions were used in the early Oldsmobile F85's from 1961 through 1963. Pontiac and Oldsmobile used the hydromatic through 1964. Buick used the dynaflo transmission to the end of 1963. They too used the turbo 400 from '64 well into the '70s.

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