A modified transmission control mechanism alters the standard shift sequence in a GM Turbo Hydra-Matic 400 (TH400) automatic transmission. Typically, these transmissions follow a P-R-N-D-2-1 shift order. This modification reorders the sequence, often placing first gear closest to the driver and progressing to higher gears with each successive lever movement away from the driver. A common arrangement becomes P-R-N-1-2-3.
This modification offers advantages in performance applications, particularly drag racing. The revised sequence enables quicker, more intuitive gear changes during acceleration, minimizing response time and enhancing control. Historically, the alteration provided a competitive edge before the advent of electronic shift control systems. The configuration remains popular in vehicles where rapid, precise shifting is paramount, and legacy transmission designs are retained.
