What is an Automatic Trans Shift Cable?
Though many modern vehicles have moved away from transmission shift cables and adapted transmission shift motors in their place, many vehicles still come equipped with transmission shift cables to change the operating range of the transmission. The operating range does not refer to the gear the transmission is currently in, it refers to the set of gears the transmission is allowed to move through when set to a specific setting by the user. These settings include park, reverse, neutral, drive, and any lower ranges. In order to select these ranges on the transmission, the gear selector in the vehicle is connected to the automatic transmission shift shaft by a transmission shift cable.
How does an Automatic Trans Shift Cable work?
When the gear selector is moved, it pushes or pulls the cable the exact amount needed in order to place the transmission shift shaft dead center in that range. The automatic transmission handles all gear changes after that point, and the driver can sit back, and focus on driving. In many transmissions, especially for dual clutch transmissions with shift cables, the shift cable does not have a hard setting on the transmission, and the only resistance felt is a feature of the gear selector assembly. These transmissions will recognize the position of the shift shaft based on the transmission position sensor.
A stretched or damaged cable will not allow proper shifting. This may cause an inability to select a certain gear, put the vehicle in park, or rotate the key to the lock position.
What are the symptoms of a bad Automatic Trans Shift Cable?
There are three ways the automatic transmission shift cable can fail, and they will give slightly different symptoms. If the cable stretches, it is likely to break soon, but the transmission should still function. Though the transmission may slip into its drive range after the gear selector is moved to that range, the stretched cable will likely require the gear selector be shaken or moved just past the desired range for engagement. For shift cables with corrosion within the sheath, the shifter may become difficult or impossible to move. Finally, a broken shift cable will provide no resistance in the gear selector lever, and the transmission will not move out of the current range. If that range is not park or neutral, the engine will not start, and the parking brake must be applied. The latter applies to neutral as well.
Can I drive with a bad Automatic Trans Shift Cable?
Vehicles will a failed or failing automatic transmission shift cable should be repaired right away. While the vehicle can operate if it moves into gear, the chances of breaking the shift cable is high, and this will leave you stranded. In cases where the transmission shift cable breaks between gears, it is likely the transmission will be locked into park, reverse, or neutral, even though the gear selector reads drive or a lower range. This can also be a dangerous situation. The best case scenario is that the cable breaks before the vehicle moves from park, but this will still leave the driver and passengers stranded.
How often do Automatic Trans Shift Cables need replacement?
Automatic transmission shift cables are actually known for failure on some models, but the majority will last at least 125,000 to 175,000 miles on average. Vehicles with known issues are generally due to extreme bends in the shift cable, poor sealing of the shift cables causing water intrusion, or issues with binding at the shift shaft or gear selector assembly. These vehicles generally give the stated symptoms in advance, and failures have been recorded before 75,000 miles.
How are Automatic Trans Shift Cable issues diagnosed?
Shift cables are simple to diagnose, especially for a trained technician who has seen them over and over throughout their career. If there is no result to moving the shifter through the ranges, the technician will check for breakage of the cable first. Also, if the gear selector shows great difficulty in shifting through the ranges, the technician will likely disconnect the shift cable to see if there is a change in resistance. Lastly, if the selector does not set the shift shaft dead center of the drive range on the transmission, the technician will adjust the shift cable, and test to see if the condition has been corrected or if the condition has moved to another range. If the condition is not corrected, the automatic transmission shift cable will be replaced.
Some cables allow for adjustment as they wear. There may also be rubber or plastic bushings at either end of the cable that will add slack to the system. It is important to have the cable inspected before replacement to avoid unnecessary repairs.
How are Automatic Trans Shift Cables replaced?
First, the trim and shift boot will be removed from the console or steering column. This grants access to disconnect the automatic transmission shift cable from the gear selector. Next, the cable is removed from the shift shaft on the transmission or transaxle before it is threaded out of the vehicle body and replaced. The rubber grommet that surrounds the shift cable where it makes entry into the body of the vehicle will be replaced, even if it is not included on the new cable assembly. Once the new cable is threaded in and connected to the gear selector and transmission, the interior trim can be replaced. Finally, if adjustment is possible and necessary, the servicing technician will adjust the cable so the transmission shift shaft position directly correlates to the gear selector position in the vehicle.
While replacing the cable, it is recommended to replace any bushings and lubricated related pivot points to extend the life of the new shift cable.