Join Date: Aug 2011
Location: Alberta, Canada
Although this is an older thread, I wanted to make a correction for anyone referencing it.
The 64 and earlier Powerglide transmission has the mount in the same location as the powerglide, but the tailshaft is 3 inches longer. the 65 and later powerglide is the same length as a TH350, but for 64 and ealier, changing to a TH350 from a PG you will need to shorten the front driveshaft.
Also, as Big Dave was mentioning about the 6-cylinder powerglide being air-cooled, this isn't true for a '62. My 62 with a 6-cylinder and a powerglide used the transmission cooler in the radiator. However, the bellhousing had a different bolt pattern for the 6-cylinder.
I also wanted to point out that top gear in the 2 and 3 speed transmissions is all the same, 1.00:1. In a powerglide, you are basically starting off in second gear when compared to a 3-speed (TH350 or TH400). Changing to a TH350 from a Powerglide will only make the car faster off the line, and will make absolutely no difference in your highway cruising RPM.
Another thing to be thought of is your engine's ideal RPM. A lot of guys change to a overdrive thinking they'll get better mileage, not thinking the cam in their engine needs higher RPM and now they're running at 1800 RPM on the highway and getting terrible mileage. It's a good idea to check the specs on your engine parts before reducing the cruising RPM, as you may be making it worse.