# Tesla Small Drive Unit



## DrJeff (Apr 24, 2015)

gtwilliams said:


> Hi, does anyone know where I can find information and dimensions for a Tesla Small Drive Unit?


I've made lots of postings about the Tesla Small (rear) drive unit.
www.teslorean.com
TesLorean on DCMTalk.org
TesLorean on DIYElectricCar

If I haven't posted them somewhere else, I can also provide rough (not CAD) dimensions.

Jeff


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## Karter2 (Nov 17, 2011)

From another thread...
https://hsrmotors.com/hsr/products/front_small_du


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## Kevin Sharpe (Jul 4, 2011)

gtwilliams said:


> Hi, does anyone know where I can find information and dimensions for a Tesla Small Drive Unit?


You can find some overall dimension for the small rear drive unit in my build thread (here).

I'm aware of ~10 cars that are currently using the Open Source controller developed by Damien and Johannes (here) and you can expect to see most of the Tesla hardware opened up this year


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## gtwilliams (Apr 3, 2018)

Karter2 said:


> From another thread...
> https://hsrmotors.com/hsr/products/front_small_du


Thank you. I'd come across this page before, but I can't find any information regarding dimensions. There's not a lot of information about the Tesla SDU on the internet at all!


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## gtwilliams (Apr 3, 2018)

DrJeff said:


> I've made lots of postings about the Tesla Small (rear) drive unit.
> www.teslorean.com
> TesLorean on DCMTalk.org
> TesLorean on DIYElectricCar
> ...


Thank you. I've taken a look and seem to have come across some dimensions you'd posted a while back. Am I right in thinking there are TWO Tesla SDUs? Front and rear? I thought there was just the SDU and LDU?


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## gtwilliams (Apr 3, 2018)

Kevin Sharpe said:


> You can find some overall dimension for the small rear drive unit in my build thread (here).
> 
> I'm aware of ~10 cars that are currently using the Open Source controller developed by Damien and Johannes (here) and you can expect to see most of the Tesla hardware opened up this year


Great! Thank you, Kevin. All very useful.


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## Kevin Sharpe (Jul 4, 2011)

gtwilliams said:


> Am I right in thinking there are TWO Tesla SDUs? Front and rear? I thought there was just the SDU and LDU?


Correct, their are two 'small' drive units, front and rear. The front DU stands more upright and has slightly different gearing from the rear.


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## Kevin Sharpe (Jul 4, 2011)

gtwilliams said:


> Great! Thank you, Kevin. All very useful.


No problem. If you're in the UK (please add your location to your profile) then Chris Hazell (here) has all Tesla drive unit variants for sale and may provide access to one for measurement if required


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## DrJeff (Apr 24, 2015)

Important consideration from a conversion point of view for the front and rear small drive units, is that for their transmission fluid pumps to work, they must be oriented as they are found in the model S. That is...

front drive unit : motor/inverter leading - differential gear following
rear drive unit : differential gear leading - motor/inverter following


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## gtwilliams (Apr 3, 2018)

Kevin Sharpe said:


> No problem. If you're in the UK (please add your location to your profile) then Chris Hazell (here) has all Tesla drive unit variants for sale and may provide access to one for measurement if required


Ha! How weird! I'm also based in Bristol, England! Thank you, Kevin!


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## brian_ (Feb 7, 2017)

DrJeff said:


> Important consideration from a conversion point of view for the front and rear small drive units, is that for their transmission fluid pumps to work, they must be oriented as they are found in the model S. That is...
> 
> front drive unit : motor/inverter leading - differential gear following
> rear drive unit : differential gear leading - motor/inverter following


It seems reasonable that these drive units must run most of the time in the normal rotational direction, but judging from the drawing and photographs that I have seen, in all cases that means that the motor is behind the axle line. The following image, one a series originally produced by Tesla Motors, shows all of the drive unit variations:








Single motor - RWD with large rear drive unit
Dual motor - AWD with (small) front and small rear drive units
Performance Dual motor - AWD with (small) front and large rear drive units

In this illustration, the small drive motors are in red, and a difference between front and rear small drive units is apparent: the front motor is on the right-hand side, while the rear motor is on the left. That might not matter. (The large rear drive unit has the motor on the left-hand side, but this illustration shows both the motor and the inverter in red.)


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## brian_ (Feb 7, 2017)

Kevin Sharpe said:


> Correct, their are two 'small' drive units, front and rear. The front DU stands more upright and has slightly different gearing from the rear.


To explain that further, I think that the front unit places the motor higher to clear the front of the extended case of the 85 and 100 kWh batteries - the overlap of motor and battery case is visible in the illustrations above.

While the HSR catalog says the gearing is the same for both front and (small) rear, I think Kevin is correct, as I have read multiple references to that gearing difference. I believe that the front unit is geared taller (less reduction), so that it is optimized for higher road speed: ~9.73:1 in the rear and ~9.34:1 in the front. Since most discussions of the gearing difference are in Performance models (which have a large rear motor), it is also possible that small rear drive units have the taller (~9.34:1) gearing as HSR says.


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## chrishazell (Oct 29, 2017)

brian_ said:


> To explain that further, I think that the front unit places the motor higher to clear the front of the extended case of the 85 and 100 kWh batteries - the overlap of motor and battery case is visible in the illustrations above.
> 
> While the HSR catalog says the gearing is the same for both front and (small) rear, I think Kevin is correct, as I have read multiple references to that gearing difference. I believe that the front unit is geared taller (less reduction), so that it is optimized for higher road speed: ~9.73:1 in the rear and ~9.34:1 in the front. Since most discussions of the gearing difference are in Performance models (which have a large rear motor), it is also possible that small rear drive units have the taller (~9.34:1) gearing as HSR says.




I will find out and post the gearing for the small front and rear drive unit in the next week or so as currently have both opened up to design a limited slip differential [emoji106]


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## chrishazell (Oct 29, 2017)

chrishazell said:


> I will find out and post the gearing for the small front and rear drive unit in the next week or so as currently have both opened up to design a limited slip differential [emoji106]
> 
> 
> Sent from my iPhone using Tapatalk



So both front and rear small drive units are geared the same. Info below.

Primary drop = 78/31 = 2.516:1
Final drive = 79/21 = 3.762:1
Overall ratio = 9.465:1



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## Kevin Sharpe (Jul 4, 2011)

chrishazell said:


> So both front and rear small drive units are geared the same.


Fascinating... so the same as one another but different from the 'large' rear iirc


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## brian_ (Feb 7, 2017)

chrishazell said:


> So both front and rear small drive units are geared the same. Info below.
> 
> Primary drop = 78/31 = 2.516:1
> Final drive = 79/21 = 3.762:1
> Overall ratio = 9.465:1


Thanks Chris! 

So the HSR catalog is correct.



Kevin Sharpe said:


> Fascinating... so the same as one another but different from the 'large' rear iirc


It makes sense. Both small units were designed for use in the AWD ("Dual Motor") models only. With two motors (even small ones), the gearing could be taller than with a single (albeit larger) rear motor. The resulting mismatch in front to rear gearing when a (small) front motor and large rear motor are combined (a "Performance Dual Motor" variant) appears to be accidental, and it is certainly harmless.

Although some fans make a big deal about Telsa's logic to choose front-to-rear power distribution for best efficiency resulting from that gearing difference, it is just making the best of the accidental situation.


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## tiger82 (Sep 23, 2015)

chrishazell said:


> I will find out and post the gearing for the small front and rear drive unit in the next week or so as currently have both opened up to design a limited slip differential [emoji106]
> 
> 
> Sent from my iPhone using Tapatalk


Have you confirmed that the differentials in the small drive units are different than those in the large drive units? If not, you can use the Quaife unit from EVTV designed for the large drive unit.


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## Kevin Sharpe (Jul 4, 2011)

tiger82 said:


> Have you confirmed that the differentials in the small drive units are different than those in the large drive units?


They are different


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## chrishazell (Oct 29, 2017)

tiger82 said:


> Have you confirmed that the differentials in the small drive units are different than those in the large drive units? If not, you can use the Quaife unit from EVTV designed for the large drive unit.




As Kevin has said they are different. But I have been working with quaife and can now offer a small drive unit abt diff. 

I have sole distribution right so if anyone wants one get in contact. Get my first delivery in about 8 weeks.

[email protected] 


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## Kevin Sharpe (Jul 4, 2011)

chrishazell said:


> I have been working with quaife and can now offer a small drive unit abt diff.
> 
> I have sole distribution right so if anyone wants one get in contact. Get my first delivery in about 8 weeks.


That's good news... lots more toys for my conversions


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## Kevin Sharpe (Jul 4, 2011)

This is exciting, Chris tweeted today;

"Check out the inside of the small tesla drive unit. We got the gear box apart and now offer an ATB limited slip differential replacement. Get in contact today to purchase yours be one of the first in the world! "

https://twitter.com/zeroevuk/status/988538706255581184


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## chrishazell (Oct 29, 2017)

Kevin Sharpe said:


> This is exciting, Chris tweeted today;
> 
> 
> 
> ...




Here’s another pic 










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## brian_ (Feb 7, 2017)

The images appear to show both front and rear drive units, which are reversed left-to-right relative to each other (because the front motor is on the car's right hand side, but the rear motor is on the left hand side). The first one (from the Tweet) would be a front unit; in the second photo it would be a rear unit on the left and a front unit on the right. Correct?

In both cases, there appears to be a pump, driven by the ring gear, in the bottom of each case. The rear unit also appears to have a fluid pipe connecting to passages in the case at the hose from the pump and to the motor bearing area. Are these lubricant pumps? Am I correct in assuming that they only function appropriately for continuous operation in the normal forward driving direction of rotation?


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## tiger82 (Sep 23, 2015)

Nice job Chris! We are very happy with the Quaife unit in our Tesla Cobra EV race car. We can lay down two perfectly matched black strips from a standing start (hillclimb) or put the power down quickly coming out of turns on road race courses.

We haven't had much success in cooling the large Model S motor yet, so we may end up running dual motors at some point in the future and will definitely be a customer for one of your units. Splitting the power between 2 motors should help the cooling situation.


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## chrishazell (Oct 29, 2017)

tiger82 said:


> Nice job Chris! We are very happy with the Quaife unit in our Tesla Cobra EV race car. We can lay down two perfectly matched black strips from a standing start (hillclimb) or put the power down quickly coming out of turns on road race courses.
> 
> We haven't had much success in cooling the large Model S motor yet, so we may end up running dual motors at some point in the future and will definitely be a customer for one of your units. Splitting the power between 2 motors should help the cooling situation.




I have come up with a coolant mod for the large drive unit that spilts the motor and inverter onto different coolant loops I will be trying it in my skyline build and in 3 stunt cars I am about to build. Drop me a message to [email protected] and I will share my finding once I have tested it will be able to provide you with a kit that you weld on/ in .


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## chrishazell (Oct 29, 2017)

brian_ said:


> The images appear to show both front and rear drive units, which are reversed left-to-right relative to each other (because the front motor is on the car's right hand side, but the rear motor is on the left hand side). The first one (from the Tweet) would be a front unit; in the second photo it would be a rear unit on the left and a front unit on the right. Correct?
> 
> 
> 
> In both cases, there appears to be a pump, driven by the ring gear, in the bottom of each case. The rear unit also appears to have a fluid pipe connecting to passages in the case at the hose from the pump and to the motor bearing area. Are these lubricant pumps? Am I correct in assuming that they only function appropriately for continuous operation in the normal forward driving direction of rotation?




Yep your correct that is a front and a rear. 

The pump sends oil into the motor housing though the heat sink that is liquid cooled. So all the windings and bearing are submerged in oil. 


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## brian_ (Feb 7, 2017)

chrishazell said:


> Yep your correct that is a front and a rear.
> 
> The pump sends oil into the motor housing though the heat sink that is liquid cooled. So all the windings and bearing are submerged in oil.


Thanks Chris. 

So the liquid-cooled motor is actually motor -> oil -> water cooled... the stator's heat is transferred first to the gear oil, then from the oil to the (water-glycol) coolant? That would make that little pump in the gearbox critical to motor cooling, and might explain some of the difficulty with cooling the motor under sustained high load.


For those not so familiar with thermodynamics: oil is a poor coolant (compared to water) because it has a low heat capacity, which means that for a given mass of oil and amount of heat, the temperature rise to absorb that heat is high. Oil is only used for cooling when water won't work (such as in a transformer) or when there is oil there anyway and high cooling performance is not needed.


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## nucleus (May 18, 2012)

brian_ said:


> Thanks Chris.
> 
> So the liquid-cooled motor is actually motor -> oil -> water cooled... the stator's heat is transferred first to the gear oil, then from the oil to the (water-glycol) coolant? That would make that little pump in the gearbox critical to motor cooling, and might explain some of the difficulty with cooling the motor under sustained high load.
> 
> ...


Exactly. Localized nucleate boiling is a major factor that makes water a far superior coolant.









Could there be a way to run a small aluminum tube with turbulators filled with water coolant through the rotor in order to cool the oil while it is still in the rotor?


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## chrishazell (Oct 29, 2017)

From my point of view the way tesla have done it is brilliant. As with the large drive unit the coolant goes though the motor then through the inverter which causes big problems as the motor is happy up to 185 degrees yet the inverter is only happy to 85 degrees there for when under load the inverter over heats very quickly due to the motor heating the coolant up before entering the inverter. 

Where as with the small drive unit the coolant loop is the same system but splits on the drive unit so goes through the inverter and the motor heat sink at the same time meaning the motor temp does not over heat the inverter and because it’s a heat sink and oil cooling for the motor the temperature allowing the cooling to efficiently cool the inverter and then only cool the motor a small amount due to the heat sink and oil temp transfer rate so I think the motor would be running at 50 degrees hotter than the inverter which is not a problem. 

Hope that makes sense  


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## Duncan (Dec 8, 2008)

Could there be a way to run a small aluminum tube with turbulators filled with water coolant through the rotor in order to cool the oil while it is still in the rotor?
[IMG said:


> http://www.usa.brauntechnologies.com/enhancement-devices/wrapped-cores[/IMG]


I just don't see that helping - water is about twice the heat capacity of oil so you would be better just flowing the oil faster than sticking tubes down the holes and restricting the flow


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## chrishazell (Oct 29, 2017)

If more cooling is required for the motor side I would just fit a larger heat exchanger as you can unbolt it very easily 


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## brian_ (Feb 7, 2017)

chrishazell said:


> If more cooling is required for the motor side I would just fit a larger heat exchanger as you can unbolt it very easily


A great potential improvement, but the oil loop is a still a critical part of the chain. Changing the heat exchanger does not change the heat transfer from motor to oil, except by lowering the cold-side oil temperature.

Since the oil pump is mechanically driven (in a single-speed gearbox), the pump speed is directly proportional to wheel speed. The gearing is chosen to avoid excessive pump speed at the car's upper speed limit, and so it is turning very slowly (relative to what the pump can handle) at normal speeds. If the oil loop's cooling capacity is inadequate for high-performance use, an electric oil pump replacing or in parallel with the mechanical pump could be the solution.


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## Ada Diamonds (Feb 9, 2018)

brian_ said:


> If the oil loop's cooling capacity is inadequate for high-performance use, an electric oil pump replacing or in parallel with the mechanical pump could be the solution.


As long as there is space in the case, it looks pretty easy to T the lines for an electric pump in parallel with the mechanical, no?


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## brian_ (Feb 7, 2017)

Ada Diamonds said:


> As long as there is space in the case, it looks pretty easy to T the lines for an electric pump in parallel with the mechanical, no?


Yes, it looks like that to me, too, but space is likely an issue and getting lines through the transmission case would not be trivial. Any external pump paralleled with the stock pump would need a check valve to avoid bypassing flow when it is not pumping (it would not be needed at high road speed).


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## Duncan (Dec 8, 2008)

Hi Guys
You have an oil cooling loop and a water cooling loop and a radiator

This sounds like a problem that Cummins had with the engine test system at our High Horsepower plant in Northalerton

This plant was set up with the cooling water going straight to the cooling tower

We had problems with the system overheating - despite having the same amount of cooling as the other plants

What I found was that the other plants used a "Hot well" and a "Cold well"
The cooling tower operated continuously to cool water from the Hot well and return it to the Cold well
The engine test would draw water from the Cold Well and return it to the hot well

This means that you get to use the full capacity of the cooling tower all the time - not just when the engine test is running full bore

So for your system I would recomend

The oil loop - you want an electric pump running at a high level all the time - I would probably remove the mechanical pump as it will limit how much oil you can pump with the electric pump at high speeds which means that it will reduce the amount of oil that you can circulate at low speeds - don't skimp on the oil but don't have too much

The water loop - add some extra capacity (water has a great thermal mass) and run the coolant pump all the time

The problem with the Cummins plant was that they only got coolant flow through the cooling towers when the test cells were running

I got them to add a couple of big concrete tanks as a Hot Well and a Cold Well and the overheating problems went away because they could run the coolant towers all the time


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## winzeracer (Apr 3, 2012)

gtwilliams said:


> Hi, does anyone know where I can find information and dimensions for a Tesla Small Drive Unit?


I have a 3d scan of a SDU Front, I can throw it on my grabcad, Large DU scan is also on my grabcad for anyone interested.

Thanks,
Brock


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## Kevin Sharpe (Jul 4, 2011)

winzeracer said:


> I have a 3d scan of a SDU Front, I can throw it on my grabcad, Large DU scan is also on my grabcad for anyone interested.


Many thanks


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## chrishazell (Oct 29, 2017)

That’s amazing I will have a look on grad cad


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## winzeracer (Apr 3, 2012)

chrishazell said:


> That’s amazing I will have a look on grad cad
> 
> 
> Sent from my iPhone using Tapatalk


Kevin and Chris,

https://grabcad.com/library/tesla-front-small-drive-unit-3d-scan-1 

Enjoy,
Brock


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## chrishazell (Oct 29, 2017)

Thanks for this very useful 


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## joekitch (Sep 13, 2013)

chrishazell said:


> I have come up with a coolant mod for the large drive unit that spilts the motor and inverter onto different coolant loops I will be trying it in my skyline build and in 3 stunt cars I am about to build. Drop me a message to [email protected] and I will share my finding once I have tested it will be able to provide you with a kit that you weld on/ in [emoji106].


bumping an older thread but...
how well did this work out? 
does it really help with motor cooling and preventing limp mode?
did you document the mod somewhere or are you keeping it under wraps as a "Shop secret"?


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## Heikki J. (Dec 30, 2020)

Also bumping this old thread. I've got a front SDU that I'm planning to run in reverse. What kind of solutions have you done for the oil circulation? External electric pump?


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## gillisk (Aug 9, 2021)

Hi All, I'm taking my small drive unit apart for the first time and I'm having trouble splitting the central case to get to the gears. I want to get in there so I can see what I need to do to modify the oil pickup since I plan to run mine upside down.

Anyway, I have removed all the bolts that hold the center section together, removed the inverter, and the 4 bolts behind it. The center case has split about a .25" all the way around but won't come apart. I may just need more force, but I also don't want to break something. Do I need to remove the electric motor?

Here's a video of my disassembly so far. Any help would be very greatly appreciated! Thank you!

I know this strays from the original post thread a bit which was asking for SDU dimensions, I used the 3D cad file from Stealth EV. There is a measure tool in the cad file.


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## Heikki J. (Dec 30, 2020)

gillisk said:


> Anyway, I have removed all the bolts that hold the center section together, removed the inverter, and the 4 bolts behind it. The center case has split about a .25" all the way around but won't come apart. I may just need more force, but I also don't want to break something. Do I need to remove the electric motor?


Hi! I struggled with the same issue and was finally able to crack it open after I bolted some square bars to the casing and used a bearing puller like in the attached image.


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## gillisk (Aug 9, 2021)

@Heikki J. Thank you! This is a nice setup. It looks like I need a bearing puller or sorts. So you are basically pushing the bearing out of the case half in order to open it up, great! Super helpful!


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## Heikki J. (Dec 30, 2020)

Yes, pushing the bearing or pulling the case. Still to see how it goes back. I tried cooling the bearing and heating the case but could get it loose. Finally ended up with this setup and then it was very easy.


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## gillisk (Aug 9, 2021)

@Heikki J. I could not get the the toothed gear off. I couldn't totally tell if the circlip I can see behind it is holding it on? I guess it doesn't really even need to come off if I am pulling the case away from the bearing? Thanks!


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## jason_arnold (Jan 15, 2014)

Thanks for sharing your (mis)adventures.

Some helpful bits in this video regarding the process for reassmbling the case (effectively the reverse of splitting it): 




FYI, it also talks about the encoder (toothed gear) as well.


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## Heikki J. (Dec 30, 2020)

I completely forgot the toothed gear. You will need to somehow get it out - I used a smaller puller and was able to pull it out. And after that you just press the axle, the bearing will remain on the case.


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## gillisk (Aug 9, 2021)

@jason_arnold - Thanks for the recommendation to watch the Zero EV video, that was super helpful.

@Heikki J. - Thanks for the extra pictures and tips. I think I should be able to break into the center case today. Really appreciate your help!


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## ViktorT (Jun 26, 2019)

Hi. Im doing a conversion in an alfaromeo 147 with a tesla SDU in the front going backwards. I will have an external oil pump for the gearbox loop. Im thinking of how to set up the cooling system. So now there is the heat exchanger to exchange glycol with the oil, the same glycol loop as the inverter. But what if I could take the gearbox oil directly to an oil cooler and then direct the same oil directly into the inverter cooling loop? Then I won't need the glycol loop and one pump less. Does anyone know the actual heat dissipation need of the inverter? If its 220kw with about 1-2% loss I would it should be somewhere around 2-4 kw heat dissipation and perhaps the double at short peaks. And I would assume the heat dissipation in the gearbox oil is much less, but I dont know exactly how much. Is this idea totally insane or would it work do you think? Is my assumption on heat dissipation correct?


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## bawfuls (Jan 8, 2018)

Is it just me or are the ebay prices on these rear SDU's going up lately? A few months back when I'd search randomly there would be several at any give time under $2k and most were around $3k, but now I"m seeing them as high as $5k and far more front unit listings.


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## Heikki J. (Dec 30, 2020)

I have noticed pretty much all the prices going up recently...


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## remy_martian (Feb 4, 2019)

bawfuls said:


> Is it just me or are the ebay prices on these rear SDU's going up lately? A few months back when I'd search randomly there would be several at any give time under $2k and most were around $3k, but now I"m seeing them as high as $5k and far more front unit listings.


Your "and far more" is a *brand new* small drive unit for under $7k. Many are at or under $2k.

So, yes...it's just you 😂


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