How does a Transmission Linkage Work?by Don Bowman
All automatic transmissions have basically the same shift linkage on the transmission itself. The shift linkage between the cabin and the transmission varies between vehicles, but still has the same function. There is a column shift and a floor shift that are both cable operated. Shift levers have even been placed on the dash on several SUVs. None of these however, are very complicated.
The arm on the transmission that is used to change gears will be common. As the lever is rotated, there will be definite detents for Park, Reverse, Neutral, Third or Drive, Second and First gears. On many transmissions, there will be a Fourth or overdrive detent. It all depends on the vehicle, but it still only uses a detent. On many vehicles, a button on the gearshift handle controls the overdrive function via a solenoid.
All vehicles today come with a lockout device that does not allow the vehicle to be shifted out of "Park" unless the brake is depressed. This is for obvious safety reasons. A small electrical solenoid actuates on the steering column or floor shifter when the key is on and the brake is depressed, freeing the shift lever so it can be moved. In the case of a column shift, when the shift handle is pulled down, the detents can be felt in each gear.
The indicator on the dash that shows the gear position of the handle is a small needle attached to a nylon cord. It is attached with a spring clip on the barrel of the column that turns with the handle. As the handle is pulled down, the barrel rotates clockwise and pulls on the indicator, dropping it into a lower gear. As the handle is raised, a spring pulls the indicator back toward park.
On a column shift, a rod runs from the handle straight down, and has a lever attached to the end of it near the brake pedal arm. The shift cable runs up through the firewall and attaches to this lever. The cable runs from the firewall to the transmission gear shift linkage, where it is attached and held securely in place. As the handle is moved, it either pulls or pushes on the cable. In turn, the cable does the same to the transmission linkage.
A floor shift linkage operates by pushing or pulling on the cable by the forward and backward movement of the lever handle. If the cable ever needs to be replaced, make sure that the transmission (the gear shift on the side of the transmission) is in "Park." When replacing the cable, make sure the shifter is also in "Park" like the transmission. Install the cable so that it fits loosely onto the transmission lever, and is secure. If the cable is left to flop around, it will flex every time the shifter is moved, and will be ineffective in changing gears.