Nissan Leaf Transmission Tear Down

by Ben N on March 17, 2020

I recently disassembled a Nissan Leaf driveline. That was essentially just taking apart the main components of the charger, inverter, motor and gearbox.

After doing that, several viewers requested seeing inside the gearbox. I was also interested in seeing inside and was curious if I could use part of it to mate with the motor for use in other projects.

So, I set to work taking apart the Nissan Leaf’s single speed gearbox.

I started by trying to drain any fluid from the case. I opened a drain plug, but nearly no oil came out. From the salvage yard, there was a tag on the entire assembly saying the fluids had been drained. I assumed that only meant the coolant though. The drain valve on the gearbox was really hard to crack open. I would have assumed that meant it hadn’t been opened!

I set the gearbox on it’s side and pulled all the case bolts out. There is a cap with three bolts which is sort of a cover over the middle shaft. I pulled the bolts, but corrosion prevented me from pulling it off. After some beating, scraping, and twisting, I got it removed.

Under the cap is a device that looked pretty strange to me at first. There was a pair of carbon brushes pressing against the shaft, but they didn’t appear to be connected to anything else. After studying it a bit, I realized that it WAS connected to the two bolts connecting the device to the case. The idea is that this grounds the rotating shaft to the case of the gearbox. This prevents stray voltage from forming currents which can arc the bearings.

Under that component was a retaining ring and washer. I removed it with my slip ring pliers. That was the only specialty tool I needed to take the transmission apart.
https://amzn.to/2Ui0Lqr

I thought I was now ready to split the case, but couldn’t be sure whether or not the black triangular device on the outside was an issue. This is the electrical end of the parking brake. I popped it off, just in case. Under that was just a narrow shaft leading into the case.

Next, I pried around the outside edge and was able to break the seal of the case. With that, I removed the one half.

Inside, we can see the overall simplicity. The first shaft is the input from the electric motor. The center shaft has two gears on it, one large and one small, to reduce the speed and increase the torque. Lastly, the differential has the largest gear and splits the power out to the two wheels.

I tried counting the gears. Assuming I didn’t lose count…
Input shaft: 17 teeth
Middle shaft large gear: 32 teeth
Middle shaft small gear: 17 teeth
Differential gear: 75 teeth.

According to Wikipedia, the Nissan Leaf gear reduction is 7.94:1
My math based on the gear count would have put it just over an 8:1 ratio.
(That’s assuming my math and counting are right! Either way, “About 8:1” is still a correct description of the gearing in this car!)

Really, the only other thing inside the gearbox was the parking brake. The mechanism instantly went “sproing!” when I pulled the case. One of the parking brake elements is spring-loaded and around a pin on the other half of the case. Even with that disconnected, I can see how the mechanism jams into the dog-toothed gear on the input shaft, locking the gears, and thus the wheels, in place when the car is in park.

Parking brake mechanism

The last thing I was really curious about is how easy it would be to remove the input shaft. The Nissan Leaf electric motor (EM57) has a relatively short driveshaft, and it has splines on it. Splines aren’t always easy to match up. I might have to find just the exact odd clutch disc, or some other source for the splines OR I could take them from the gearbox.

I lifted straight up on the input shaft, and it slid right out. The shaft is mostly hollow, to allow space for the motor drive-shaft. It also has two bearings and the gear for the parking brake.

I slid the shaft onto the motor driveshaft and it popped right in place. An o-ring and matching groove insure a good fit.

If I wanted to extend the drive-shaft, support it, maybe even attach something like a flywheel to it, using the input shaft from the gearbox might be one way to do it. At this point, I’m considering using this motor for an electric tractor conversion, but the main concern is about supporting a large flywheel.
But that’s for another day….

Gearbox input shaft slid on the motor driveshaft.

It’s certainly interesting to be able to crack something open and see how it works. I can probably even put it all back together, although I’m not so sure about the parking brake elements!

Until next time, stay charged up!
-Ben Nelson

PS: It turns out Wikipedia is wrong! At the suggestion of a YouTube viewer, I just manually spun the output gear and counted the rotations of the input gear. You won’t believe what it came to!

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