• To pull or not to pull: Towing cars with auto transmission


    Sometime ago, I came across a discussion concerning how to tow a car with an automatic transmission. In the discussion, some were saying just put in neutral and you’re good to go–no need to place the car on a flatbed trailer. Some were even saying to disconnect the drive shaft. If you read through the owners’ manual, it says there that it does not recommend towing the vehicle (with automatic transmission) by just putting it in neutral. If done so, the transmission could be damaged. It recommends that the vehicle be placed on a flatbed truck to transport it. But a car with a manual transmission has no issues when it is towed; just put it in neutral.

    From the last time I read the thread discussion, I did not read a viable explanation why it was not advisable for a car with an auto tranny to be towed by simply putting it in neutral. So I went back to my references…

    In a manual transmission, you have the basics: input shaft; output shaft; gears; shifting forks; and hamsters. That’s it. Lubrication is by splash type, so when the gears turn, oil splashes all over the place.

    But when you open up an automatic transmission you will find oil passages, clutch drum, clutch linings, more hamsters and planetary gear assemblies. Now when two gears are in mesh, one will turn clockwise the other counter clockwise. To make them turn in the same direction, you add a third gear between them. Another way to make them rotate in the same direction is to use a small external gear inside an internal gear. Putting another gear in the center and meshed with the external gear creates a basic planetary gear system. Now, with this system you could provide speed increase with torque decrease, speed increase with torque increase, direct drive, reverse direction of rotation or neutral (input shaft and output shaft disconnected). A planetary gear system has the sun gear (in the center) meshed with two external gears (planet pinion) and they are meshed to an internal ring gear. By locking anyone of these gears, you can change the direction or the speed of the gears. These are done by the use of a brake band that wraps around the clutch drum or by a series of multiple clutch discs inside the clutch drum. Now these are actuated by hydraulic pressure. Now, even the lubrication of the gears are by hydraulic pressure. The automatic transmission fluid or ATF is used for lubrication and hydraulic purposes. Basically, the automatic transmission works on hydraulic pressure. It functions on hydraulic pressure.

    Now, according to my reference, the vehicle may be towed for a short distance and at low speed. But it also states that the transmission is only lubricated when the engine is running. Hmmm… that makes sense. So if you just put your car in neutral and start towing it, you can damage the internals. Your output shaft is connected to the planetary gear. That could be damaged. Far fetched? True, but why risk it?

    Looking at my reference, the governor is also connected to the output shaft. This device helps in the shifting of the transmission. It receives pressure from a pump then sends low hydraulic pressure to the shifting solenoids. If there is no oil pressure, the governor could be damaged.

    After doing some reading regarding this topic, it made more aware of how easily one could damage an automatic transmission. If ever you do need to have your car towed and it has an automatic transmission, do request for a flat bed type of a tow truck. It will you save a lot of trouble later on. If the tow company insists on towing it, ask them if they will pay for the damage to the transmission. Oh by the way, try signing up with the Automobile Association of the Philippines (AAP). I trust them more when it comes to towing vehicles.


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