M-40 Turbo 400 Hydramatic Transmission 3-spd

DublinMark

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Greetings new to forum! Has anyone replaced the 2-spd Powerglide with a 3-spd M-40 transmission. These seem to be available used for around $400 +/-. I'm looking for better performance and cruising (fuel economy). Does anyone have appx fuel economy making the switch city/highway and is the overall performance improved in your opinion especially on highway?

Is this something you'd do at an established dealership or look for a local repair shop specializing in GMs? I'd read in a couple of places where folks recommended dealerships and there is a 60-year old GM (formerly Pontiac) dealership a few miles away.

thanks,
Mark
 

melsg5

Staff member
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The top gear is the same so there is no fuel economy increase. You should be looking at a 700R4 conversion. Top gear is an overdrive gear. I doubt a GM dealer will do the conversion.
 
G

G-964884

The top gear is the same so there is no fuel economy increase. You should be looking at a 700R4 conversion. Top gear is an overdrive gear. I doubt a GM dealer will do the conversion.
Thank you I need something better than 1:1 correct. Happy thanksgiving
 
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