Quote:
Originally Posted by R.I.D.E.
Actaully a ratio of 1 to 1 is direct drive (engine speed-pinion shaft speed identical). In some 4&5 speeds the main shaft and input shafts are directly connected in 4th gear. Nissans are my experience particularly RWD versions.
One customer lost the key in the countershaft front gear and the transmission only worked in 4th gear, all others requiring the countershaft to transmit torque. He drove 250 miles home with only 4th gear. 3 decades later he is my family doctor.
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I think you are are talking about a subsystem in an automatic, if I'm correct in thinking direct drive is the same as lock up. This is when the torque convertor physically connects to the transmission, as oppose to pushing fluid through fan blades. Thus lock up was more efficient during cruising.
In older automatics, the lock up only occurred in the highest gear. In modern transmissions, it can occur in nearly any gear.
Overdrive isn't limited to a type of transmission. It is just a term for those higher speed gear ratios, whether they are in an automatic or manual.
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