To maintain control while driving in the mountains recently (in a snowstorm), I had to downshift my automatic transmission, and then upshift, and then downshift again, etc., many times over – could this have done any damage to my transmission? It seems to be fine, but I’m wondering.
Thanks, Patrick
Patrick, the short answer is no, you will not damage an automatic transmission by up and downshifting it manually.
But to qualify that, transmissions are designed to shift under “normal” conditions. This means low, moderate and limited high-engine speeds as well as low, moderate and limited high loads on the powertrain –the engine, transmission and final drive (rear axle in the case of rear wheel drive, or output axle in the case of front wheel drive.
Transmissions are designed to shift thousands of times in their lifespan, but by forcing it to shift manually, you limit the ability of the module to control shift points at any given speed and load of the powertrain.
A driver who is not aware of powertrain speeds or loads could put a transmission in a compromised condition by forcing it to shift when it normally wouldn’t want to shift. Fortunately, most powertrain control modules prevent up or downshifts that may be too radical for the powertrain to survive. My Venza is a perfect example of that.
Even just coasting to a stop from 50 km/h, the control module will not let me downshift, or gear down, if the vehicle is travelling faster than about 20 km/h. On the other hand, I was driving a new Jeep Grand Cherokee last week and it let me pull down to first gear at 50 km/h. It all depends on what the manufacturer intended for the vehicle’s normal use.
Back to your question – do not downshift at an engine speed that will pin the tachometer at the engine’s red line, and do not downshift with your foot trying force the gas pedal through the floorboard. Flooring the load pedal puts the powertrain into full load and if engine speed is too high, you could end up pulling over to the side of the road to pick up pieces of your vehicle.
Oh – and Patrick, a tip: If you find yourself on icy roads (hills or flat) and you need to haul your car down to a stop, place the transmission in neutral as you slow to about 40 km/h. This removes the torque from the drive wheels allowing the brakes to slow down the vehicle only. With an automatic transmission still in gear, the brakes will be forced to slow down the engine as well as the vehicle. Anyone that has driven a stick-shift transmission will attest to the effectiveness of this strategy.
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