That particular transmission was indeed a 4 speed, but 4th was 1:1, no overdrive. First gear was very low ratio, since it had a fluid coupling that did not multiply torque like modern-day torque converter. It was a very popular drag race transmission back in the 50's and 60's, essentially the trans upon which companies like B&M built their business. Manual overdrives were popular in the same era, but the first automatic overdrive I ever saw and drove was a pre-production prototype installed in a '69 DeVille, which was a TH400-based unit. As a freshman engineering student at General Motors Institute, I was quite impressed while driving across I-94 at 90 mph with the tach barely at 2000 rpm. I suggested to the veteran engineers this would be a great deal in a GTO, GS or the like, enabling deep gears while still keeping the big blocks in a respectable RPM range at pre-55 mph law highway speeds. My reply was "That's not the objective, kid. We're gonna have some tough fuel economy regulations in the next few years and it's gonna take stuff like this to enable us to still build big cars with big engines. Besides that, it's too big and heavy for anything but a B or C body"86-blk442 said:
Working at a GM dealership during the 80's, I thought of that prototype often when I'd see all the issues with the early 200-4R's. That original prototype still lives on as the 4L-80 in the HD trucks and as the man said 40 years before, it's too big and heavy for anything else.
Bill
