I seem to remember when I bought Millicent, the Allison MT643 transmission would stay locked to the engine at all times, so that I always had engine braking. Slowing to a stop, the engine would rev up with each downshift, and stay with vehicle speed all the way down. Then at some point that changed, kind'a suddenly. Now it freewheels a lot, and we smoked the brakes a bit down Ashland Grade on a recent trip.
Frankly, I don't know quite how the transmission is supposed to work. But I found this information on Industrial Automatic's web site: "Automatic lockup clutch, throttle-modulated for maximized fuel economy and enhanced engine braking." This in addition to the fact that the lock-up feature is supposed to be effective in 3rd and 4th gears. Who can explain this to me? There is a cable that connects to the throttle linkage at the engine, and to the tranny at its left rear. I need to know how to adjust that cable.
And I once read that the tranny will self-destruct if the cable is broken -- although that pertained to the AT5-series tranny.
If you can direct me to a web site that explains all this, I would be most grateful!