Don sounds like the kind of guy who'd have a seat on our bench, though not sure we (or anyone) could replace a head gasket for £50 these days! We really enjoyed reading your comment and thank you for your kind words! We hope that BMW #19 is an i3, or if not that #20 will be 🙂

@@wiselyauto I intend to buy a 42kwh version and I understand the end of leases coming up in October will provide the perfect opportunity. I do believe it will be my 20th Beemer.

www.greencarreports.com/news/1082061_bmw-activee-motor-failures-the-price-of-leasing-a-test-car “The drivetrain housing assembly in those vehicles may not have been adequately sealed at the factory, meaning that gear shaft was not sufficiently lubricated. Over time, the connection between the electric drive motor and the gear assembly could become worn--and fail suddenly In the case of this sudden failure--experienced by more than a dozen BMW ActiveE drivers--the loss of lubrication over time would cause the gear to grind on the electric motor output shaft until one or more splines failed”

@@wiselyauto Interesting. When one reads the actual recall documents even they do not clearly describe the failure or show failed parts, except for a failed transmission input seal. www.nhtsa.gov/vehicle/2011/BMW/ACTIVEE#recalls I believe the failed splines they are referring to occur on the other side of the transmission input shaft, inside the transmission, caused by low oil level in the transmission due to the faulty input seal. Their picture of a failed seal (#47) shows oil glistening on the housing and pooling up below it. I also notice that your car had the improved motor output with the closed end, as opposed to the older open-ended part shown in picture #26 of the repair bulletin. In any case, did you notice leaking lubricant/a failed transmission input seal on this car? When you show the motor output the metal shavings appear dry and powdery, not as you would expect if there was indeed a failed input seal.

I get your point regarding the splined interface being a static connection. I am guessing the wear on both sides of the connection caused the failure that they fixed by sticking on a new or salvaged gearbox - which gave just enough bite for long enough to move the car on to an unsuspecting new owner! There are many high mileage i3s out there that have not suffered the failure so I wonder what caused it? Maybe the bolts between the original gearbox and motor came slightly loose allowing movement. Or there was a tiny alignment fault in the manufacture of the motor or gearbox. With the torque coming out of the motor, that connection has to be 100% perfect but then for it to be that perfect (tight) it would be very hard to assemble

It's not really static if the motor turns backwards in reverse. The joint will rock slightly with each change in direction. I do think your idea about the splines being different is plausible. Maybe that later gear boxes have a harder temper than the older motor splines. If that's the case, you could consider the gear box and motor to be a matched set so, you should never switch just one.

​@@gap9992 having now had a chance to think it all through, consult with a few people and generally assess all the evidence available to us, we have reached the conclusion that your theory is likely the most accurate. We believe that BOTH the teeth/splines on the original trans/motor wore down to the point where the transfer of power was inhibited (Why? This we'll never know but you have offered some reasonable suggestions). Then... whether knowingly or unknowingly, the (lesser) wear on the motor's splines was not addressed and a new trans was fitted. The fresh teeth on the brand new input shaft provided just enough bite to keep the power transferring for a few thousand more miles / to sell the car to an unsuspecting new owner. Second time round, the failure happens faster and is more pronounced, as this time there is a bit of slop/play between the fresh teeth and the already pre-worn splines on the motor output. It could almost be argued that a lower mileage car is more susceptible to this wearing down due to the constant switching of torque direction.

I was thinking of the same.

But as he mentioned internal spline integral to the rotor which is (almost) perfectly balanced in the factory with lots of permanent magnets and laminated sheets which are (I guess) riveted together.

It's definitely something we will look into if this becomes a more common problem. Better for the environment and the wallet to repair instead of replace...

@@wiselyautothat would not hold 200 lb ft of torque however tight it might be fitted.

It was the splines in the motor ( the female part of the coupling) that had stripped. The shaft on the gearbox was ok. So to do what you suggest the motor would have to have been disassembled, which is a specialised procedure especially if it's a permanent magnet motor. Then machined as you described. You might glue the splined bush in. If done faultlessly with the right industrial adhesive it might work, maybe. But the labour cost to spin the dice would likely be way more than £1500.

Let us know how your case develops! 🙏

​@@Pajune Recently bought a 100 mile used 2018 drive motor, and a zero-mile transmission. Next is getting all the required "small"parts (about $600 new), then get busy...

Haha, it pained us to see this too but if we can't correct things we're not being asked to / paid for unfortunately. Front wheels didn't come off for this job - we did put the rears back on the correct way round though, so at least the issue is halved in severity :)

great job You know the i3 like the back of your hand. A small question for maintenance of the box. Can the filling be done by the air vent on the top of the box without having to remove the transmission? Thanks

I'm hoping these questions will be answered 😅 I've been eyeballing one relatively cheap 2014 model with 210tkm on its electric motor, and would not be surprised if it needs the motor to be changed because of these stoopid bearings.

Search this with "i3 electric motor bearing problem". It seems to be a known issue until 2018 models! You are prolly going to need a new electric motor from what I've read.

That’s how an Ev is normally driven. That certainly has an effect but the problem shown here looks like a huge fretting of rotor internal gear teeth either by severely corroded part prior to installation or by lack of proper heat treatment ie harder male part mating with softer internal part.

The video suggested it was assembled without grease. This would leave it vulnerable to corrosion and also fretting if there was any clearance at all between the splines. There also seems to be an issue with motor output bearings (from comments here) so the motor output spline could be wobbling about, which could cause it to destroy the spline.

But what?

@@benbaselet2026 .. she comes with a baggage full of surprises :)

@@Pajune 18 months with mine and none yet popped up :)

@@benbaselet2026 That's great! I wish thousands of happy km's for you! May I ask you which year model do you have? Battery size, rex? I've been looking at a high mileage 2014 model, but it seems like a very bad idea 😂

@@Pajune 2019 BEV, 120 Ah. I very specifically wanted a commuter car and not the REX (especially the heat pump comes more in handy for me in Finland).