I am fairly sure that the Cadillac convertable diville came with a four speed auto. transmission. The car now has about 70 k miles and the transmission only shifts 3 times. The car has been in the hands of my sister and her husband. They say the trani has never been out of the car but, they did pull a trailer to Florida from Michigan once. Can any thing cause the overdrive gear from shifting and still allow the other gears to run strong?
If Im reading you right, you have a 70 DeVille Convertible? If that is so, then you have a 3-speed THM400 transmission. The early hydramatics, 41-64 in Cadillacs, had 4-speeds, but a 70 would be 100percent guaranteed to have a 3-speed from the factory. So, if thats the case, you can now sleep at night.
By the way, the 4-speed reappeared in the early 80s for Cadillac with the THM-2004R, which was pretty crappy.
I hope that helps you out.
Rob
66 SDV
Victor,
Your trans does not have a 4th gear, OD, Lock-up converter, or anything else.
It would be nice if they did, to get better fuel economy, but 3 gears is all you have to work with.
Brian