The overdrive transmissions with O.D. were like the non O.D. in the sense they were not high performance but they worked good when set up correctly..Not sure of the year but GM started installing fully syncronized three speeds in the later sixties..Pretty rare though..I had a 1967 El Camino that was factory stock with a 327 and three speed with O.D...It got great mileage and was great to drive in the city because you could use second gear and shift from low to high and vice versa...I grew up with overdrives and they were good for the lower horse power engines..My Willys four cylinder could cruise all day at 60MPH and get better than 30MPG..At 25 cents a gallon it didn't cost much to get around..I would put more overdrives in my Chevy trucks if I could find them..Especially the inlines I have..With todays gas prices it would be great to get the better mileage plus be able to get on it somewhat..All of GM's three speeds were pretty tough..You just can't abuse them much by speed shifting..Of course all the American manufactors built them at one time or another..and they too were not high performance..You will probably pay a good price for a good one..I keep checking the parts yards..They do show up once in a while..Always pull the side cover of any transmission to check for wear and damage.A guy tried to sell me a 1964 three speed with O.D. and after closer inspection I found the O.D. to be beyond repair..Overdrive seemed to go away in the 70's..In the eighties they seemed to reappear some..I might look for a newer one that I can fit into one of my older trucks.. It will probably be a manual shift but that would be OK..You can buy new O.D. units for a healthy price..That is another subject...Good Luck...AL...
