Here’s the basics of how an automatic transmission works in your car.
Here’s a few photos of the tear down I did on my Toyota Corolla’s 4 speed automatic tranny:
For more details on how I removed the engine and tranny on the Corolla, see my engine removal video here:
The major components of an automatic transmission are the case, planetary gear set, clutch packs, valve body, differential, oil pump and externally, the torque converter.
Pan removed:
With the valve body removed, we can see the guts, including the 2nd gear clutch bands and some clutch packs. Along the side are accumulator pistons.
With the bell housing opened in half, we’ve got full sight of the input shaft, which carries two planetary gearsets, the counter shaft which has one planetary gearset, and the differential that the axles plug into.
What’s interesting is this is the parking pawl that holds your car from rolling when you park up. Even more reason to use the parking brake.
A closer look at the input shaft. The torque converter powers this. Its hollow and has oil feeds for the torque converter and oil pump.
For more info on how the torque converter works, see my video here:
The guts of the tranny is its planetary gear sets. It achieves different gear ratios by holding one of the three components (planet carrier, ring gear or sun gear) steady and using the other two as inputs and outputs. The selection of these are controlled by the clutches.
The final drive of the tranny is the differential. This splits power left and right between the axles on a FWD car. The fluid is shared within the transmission.
The valve body is the brain of the transmission. It is responsible for directing fluid through the accumulator pistons and the clutches to change gears.
The tranny oil pump sits at the front of the transmission and is powered by the torque converter. It provides fluid flow throughout the tranny so valves and passages can create pressure to make things work.
And that’s pretty much all the major components that go into a transmission. It’s quite complex and there’s a lot of thought and engineering put into making these things work and last a long time. I appreciate the work of these powertrain engineers!
Here’s a few photos of the tear down I did on my Toyota Corolla’s 4 speed automatic tranny:
For more details on how I removed the engine and tranny on the Corolla, see my engine removal video here:
Pan removed:
With the valve body removed, we can see the guts, including the 2nd gear clutch bands and some clutch packs. Along the side are accumulator pistons.
With the bell housing opened in half, we’ve got full sight of the input shaft, which carries two planetary gearsets, the counter shaft which has one planetary gearset, and the differential that the axles plug into.
What’s interesting is this is the parking pawl that holds your car from rolling when you park up. Even more reason to use the parking brake.
A closer look at the input shaft. The torque converter powers this. Its hollow and has oil feeds for the torque converter and oil pump.
For more info on how the torque converter works, see my video here:
The guts of the tranny is its planetary gear sets. It achieves different gear ratios by holding one of the three components (planet carrier, ring gear or sun gear) steady and using the other two as inputs and outputs. The selection of these are controlled by the clutches.
The final drive of the tranny is the differential. This splits power left and right between the axles on a FWD car. The fluid is shared within the transmission.
The valve body is the brain of the transmission. It is responsible for directing fluid through the accumulator pistons and the clutches to change gears.
The tranny oil pump sits at the front of the transmission and is powered by the torque converter. It provides fluid flow throughout the tranny so valves and passages can create pressure to make things work.
And that’s pretty much all the major components that go into a transmission. It’s quite complex and there’s a lot of thought and engineering put into making these things work and last a long time. I appreciate the work of these powertrain engineers!
