CC Videos: How Automatic Transmissions Work

At our recent post of videos showing how manual transmissions work, there were a few commenters saying that it was the workings automatic transmissions that were still something of a mystery to them. Well, here’s a couple of well-animated videos that should help.

These focus on the most common type; the torque converter planetary-gear automatic, in this case the six-speed Allison 1000 as used in GM diesel HD pickups and such. There of course other types, but let’s focus on this, even if conventional automatics are starting to be increasingly replaced by CVT’s, which are actually very easy to understand.

This first video is pretty good, covering the basics with lots of 3D graphics.

Trying to perfectly understand the dance of planetary gear sets, especially when there’s multiples of them can be a bit daunting. The key elements are to understand how a torque converter works (below) and a basic conceptual understanding of the magic of planetary gear sets.


Here’s two videos on torque converters. I have some mixed feelings on this one, as it starts a bit backwards, with the torque converter’s ability to disengage the engine from the wheels under braking. Seems to me that explaining how it gets the car underway should come first.


This one is a bit more narrowly focused, but in a good way, with perhaps better graphics in some key aspects. Between the two, you should be able to get a pretty good idea of how they work.

If those are a bit to…um, modern for you, with all those fancy graphics, here’s an Army film from 1954 on fluid couplings. Note that the fluid coupling lacks the stator that allows the torque converter to amplify torque. That requires fluid coupling automatics, like the original Hydramatic, to have more gears, to be able to start from rest without the benefit of torque amplification.

Hope this helps. The dance of the various planetary gear sets can be a bit complicated to fully divine, and there are of course variations of them, but as long as one understands the basic principle, the rest can be left to the transmission. it’s an automatic, after all.