Originally posted by 2deep2:
Actually on most, if not all automatic transmissions, when you push the O/D button it's not another gear.

Although you are changing gear ratios, the reason for the change has to do with lock or unlock torque converter.

When the TC is unlocked it will act as another gear ratio.

If you have your shifter in drive you should get 4th gear with a 4 speed auto trans regardless O/D on or off.

In that the TC is a viscous couple, its not efficient and you get better fuel economy with it locked when traveling at constant speeds.

For fast acceleration and starts from a stand still you want the TC unlocked to gain from the advantage of the extra gear ratio.



From the Ford Technical Service Publications Manual (emphasis mine):

"The transaxle range selector lever has six positions: P,R,N,D,2,1. In addition, a transmission control switch (TCS) allows the driver to prevent a shift to fourth gear (Overdrive) and uses engine compression to help slow the vehicle (engine braking) in second and third gear."

It may not be the case on most other transmissions, but it appears to be the case on the CD4E, at least according to Ford.

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