The Secret of the GM Automatic: From Vegetable to Beast
The TH400 is GM's legendary three-speed transmission, which in the 1960s turned ordinary family Buicks and Oldsmobiles into true sleeper cars. Simply filing down the weights or changing the springs in the regulator shifted the shift points from 3,000 to over 5,000 rpm. Cheap, fast, and effective—a sport mode without electronics or chips.