The "Overdrive-4" manual transmission provides final overall rear axle ratios of 2.36:1 with six cylinder engines and 2.15:1 with V8 engines.
The transmission can be ordered on sixes equipped with 3.23:1 rear axle ratios and V8's with a ratio of 2.94:1.
The new transmission can provide fuel savings, compared to a similar car equipped with the standard three-speed gear box.
The transmission gear ratios are: Low, 3.09:1; Second, 1.67:1; High, 1.00:1; and OD, 0.73:1, resulting in the overall axle ratio in overdrive position of 2.36:1 with the six cylinder engine and 2.15:1 with the V8.
The Overdrive-4 provides a decrease in engine speed of some 18 percent in relation to the overdrive system last used in 1959 -- some 15 years ago -- on Chrysler Corporation cars. At that time the overdrive matched up with a 4.10 rear axle on six cylinder models and 3.91 ratio on V8s. The final overall ratio then resulted in a 2.87:1 axle ratio for sixes and a 2.73:1 ratio for V8 models.
The forward shift pattern of the transmission is similar to that of the traditional "h" pattern common in four speed boxes. Low gear is top left, second bottom left and high top right. When the driver wants to engage the OD gear, he shifts to the bottom right position.
In addition to the improved fuel economy the new transmission should result in less engine wear due to lower revolutions per minute at cruise speeds, less fan noise and power loss and less engine noise. The car retains its around-town gearing and has trailer-tow capabilities, which are not available with extremely low numerical ratios without the overdrive gear.
Production of the Overdrive-4 manual transmission is slated for early December and cars should be available to the public in the latter part of that month.