Gear Vendors are overdrive by .74 I believe. With all of the new overdrive automatics out there, they are kind of old school. However they are bulletproof. Lots of use in drag racing. they shift by solenoid so you can control each gear in and out both, or leave it automatic for high gear only. Great for towing I think. So you have a six speed TH400. It was my way of upgrading my SUB for towing with 410 gears, but I never towed a lot, you know how that is; just ready to go. I live 10 miles from the mountains and it is handy on grades both up and down. They cost around 2200 new in 1988 or more by now I would guess. they run on Dexron fluid. THey originated in Britain as Austin Healy used them. The original company was Lacock Ind. B4 Gear Vendors bought the patent. I never used it as underdrive, actually your low transmission gear is the lowest you have. Then if you start out in overdrive 1st gear you can downshift by .74 to your actual low gear ratio. It downshifts on command from any gear at any speed so you have to watch the downshifts. Chad.