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Old 02-23-2006, 05:25 PM   #8
Freedom
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"Overdrive" as has been stated, is basically another gear, but it is unlike the others in that it is "overdriving" the output shaft. This means that the input shaft on the transmission is actually turning slower than the output shaft. This also means that you have more "speed" and less "power" to the wheels. "Power" (torque) and speed are related in an inverse equation, so as you overdrive or shift to a higher gear, your engine has to work harder so the transmission wants to downshift. This is where the problem arises in that it down shifts and then if the hill isn't steep enough it shifts back up - back and forth. This is called "hunting" - the transmission is trying to find (hunt for) a gear that matches the load put on it. If you have a tach, you can see the engine RPM increasing and decreasing as the transmission shifts back and forth. This can happen in other gears, too, not only Overdrive. If your transmission starts hunting, shift to a lower gear- OD to 4th, 4th to 3rd, etc. Some transmissions, particularly those on vehicles with a towing package, come with a "Tow" button which takes a lot of the problems out of towing in overdrive. The tow button changes the shift points on the transmission and doesn't allow it to leave the torque converter out of lockup for extended periods. This makes the transmission run cooler. Cruise control is OK to use as long as you monitor the transmission for hunting or for downshifting more than one gear at a time. If you hit too big of a hill the cruise may downshift too many gears, making the engine red-line. That's not good!
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