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For some time now, my 1955 Desoto Diplomat hasn't shifted from 3rd to 4th. I had the same problem with my 1970 Pontiac LeMans and my 1972 Cadillac. What's the problem with the gears in these old cars? What's going wrong over time?
I'm not a transmission expert, but that seems like it might be a seal that is not allowing it to build the pressure it needs to shift properly. You might try contacting Hennie Jacobs from the club. He used to own a transmission shop in South Carolina that his son now owns. You can find his contact information in the last roster.
Annet- Your 1970 Pontiac and 1972 Cadillac would have had only 3 speed automatic transmissions. With your 1955 Diplomat having a Plymouth chassis and drive line, if it's automatic it will have a 2 speed automatic transmission. If it has a clutch, it could either be a 3 speed manual or a 2 speed semi-automatic with low and high ranges (possibly left over from 53-54). If it's a semi-automatic, you won't be able to put it into the 1st gear position on the standard H pattern column shift, only low (2nd gear position) and high (3rd gear position).
Let us know which transmission you have.
I was daydreaming while writing this post. My Pontiac problem is solved. I didn't know the car only had a three-speed gearbox. Now that I do, I see the solution in an overdrive gearbox because I don't want to drive at too high revs on the highway. I'm looking for a GM-200-4R here in Thailand.
My Desoto hasn't had an original engine for years, but a Toyota drivetrain. I completely forgot about it, because most old American cars here have Nissan or Toyota engines. It stopped shifting, but with that, I can easily go to any garage here. They know a lot about Toyota engines and transmissions.
Sorry guys, next time I'm confused, I promise not to post on this forum anymore!
Annet...good practice regardless of transmission type is to first check and thereafter religiously check fluid levels and ensure you have adequate fluid in the transmission. Many transmission shifting issues have been resolved by topping off the fluid level. Good luck!
