# Mounting leaf motor gearbox ideas



## CanadaLT28 (Oct 15, 2011)

Here is mine. It seems more of a first draft but I may keep it


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## electro wrks (Mar 5, 2012)

It looks like you have some cracked and broken aluminum castings on your motor/inverter(M/I). You should probably deal with those first. 

Next, I would mount the M/I onto the sub-frame, since you already have it. I would clear out the area where it's to be mounted under the vehicle. Lower the vehicle onto the M/I/sub-frame(M/I/S) or raise it up under the vehicle to check for initial fit and clearance. 

Next, you want to evaluate the suspension. Will the existing hubs and control arms, if it has them, work with the sub frame? Are you going to use the Leaf hubs and suspension parts? If it has leaf springs, will a de Dion axle fit in the available space? If necessary, someone specializing in fabricating trailer axles could probably make up a de Dion axle for you.

With these decisions made, you can proceed with the fitting of the M/I/S closer to its final location. The 4 perimeter mounting points on the sub-frame are a very convenient mounting system for the sub-frame. Do they and other parts of the sub-frame need to be cut off, repositioned, and rewelded? Do the mounting points on the vehicle need to be reinforced? At some point, you'll probably need to cut a hole(s) in the floor for vertical clearance. Shock and spring towers/mounts, if used, will need to be designed, fabricated, located, let-in to the vehicle chassis/body, and welded into place.

If you want to evaluate the suspension geometry throughout the wheel travel, it's a good idea to just tack-weld the parts in place. This is so they can be easily cut and moved later, if necessary, to adjust the geometry.

The half-shafts will probably have to be made-up to match the trans axle output to whatever hubs are used. 

Does any of this give you some good ideas?


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## zippy500 (Apr 3, 2017)

electro wrks said:


> It looks like you have some cracked and broken aluminum castings on your motor/inverter(M/I). You should probably deal with those first.



Thanks for the ideas.

You have me concerned now can you elaborate on where the cracked and broken aluminium castings ?


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## brian_ (Feb 7, 2017)

How valuable the Leaf front subframe might be depends in part on the car it's going into, and what will be used for suspension. For instance, if it will be used with a McPherson strut or perhaps double wishbone suspension, you might be able to use the Leaf arms and the subframe would be ready to use with them. So... it's going in the rear of something, but what, and with what suspension?


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## brian_ (Feb 7, 2017)

electro wrks said:


> It looks like you have some cracked and broken aluminum castings on your motor/inverter(M/I).





zippy500 said:


> You have me concerned now can you elaborate on where the cracked and broken aluminium castings ?


From some angles it looks like the stud hole in the front left mount area looks cracked, but from above it looks like an intentional slot.

electro wrks, is that the only one?


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## zippy500 (Apr 3, 2017)

brian_ said:


> How valuable the Leaf front subframe might be depends in part on the car it's going into, and what will be used for suspension. For instance, if it will be used with a McPherson strut or perhaps double wishbone suspension, you might be able to use the Leaf arms and the subframe would be ready to use with them. So... it's going in the rear of something, but what, and with what suspension?


Its a 1973 BMW its going into, I want to keep the original double wishbone suspension setup. Thats why I'm thinking I wont need the whole subframe.

Going to start stripping the back end of car this weekend, That is a large subframe to get in.


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## brian_ (Feb 7, 2017)

zippy500 said:


> Its a 1973 BMW its going into, I want to keep the original double wishbone suspension setup. Thats why I'm thinking I wont need the whole subframe.


That looks like a typical 1970's BMW, complete with the classic semi-trailing arm suspension. It is not a double wishbone design at all.

With this suspension the Leaf subframe is not likely workable. I'm not convinced that the Leaf drive unit (motor and gearbox) will fit at all, without the motor housing running into the right-side suspension arm and/or the right-side spring. The Leaf's drive unit configuration and McPherson strut suspension work with each other, but the drive unit was never designed to work with semi-trailing arms.

The other challenge is that it looks like the motor will try to occupy the same space as the structural rail areas of the body which runs to the right side of the final drive (diff) housing. The Leaf unit is much taller than the original final drive, especially with the inverter still mounted on top of the motor (as shown in the first post); at least the converter and charger are not still on top of the inverter.


One detail to keep in mind as you work out the installation and a subframe: the BMW's existing suspension subframe consists of a beam running across the car and carrying the suspension arms, plus the final drive or structure around it forming the third arm of a sort of T-shaped structure, presumably attached to the car by those two horizontal bolts at the back of the final drive housing. Assuming that the Leaf drive unit is not used as part of this structure, you need some framework to connect the beam to the point where the final drive currently mounts.


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## zippy500 (Apr 3, 2017)

brian_ said:


> The other challenge is that it looks like the motor will try to occupy the same space as the structural rail areas of the body which runs to the right side of the final drive (diff) housing. The Leaf unit is much taller than the original final drive, especially with the inverter still mounted on top of the motor (as shown in the first post); at least the converter and charger are not still on top of the inverter.
> 
> 
> One detail to keep in mind as you work out the installation and a subframe: the BMW's existing suspension subframe consists of a beam running across the car and carrying the suspension arms, plus the final drive or structure around it forming the third arm of a sort of T-shaped structure, presumably attached to the car by those two horizontal bolts at the back of the final drive housing. Assuming that the Leaf drive unit is not used as part of this structure, you need some framework to connect the beam to the point where the final drive currently mounts.



I am planning to remove the whole boot floor area

I am thinking to cut and remove the cross beam that supports the diff at the moment.

Was even thinking of separating the invertor from the gearbox

One question. If i mount the gear box say 3" of centre from the drive shaft will the CV joints be OK with that or do they need to be in line?

Only reason for this route is the ongoing issue with coupler for the leaf shaft, or I would go conventional route with mounting to the cars gearbox.


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## Duncan (Dec 8, 2008)

Hi Zippy

You can move your diff (in the leaf transaxle) a good bit further back than the BMW's diff is
The CV joints will work fine

If you have a look at the way the driveshafts work in the BMW I bet that they normally droop about 70mm to 150mm - so they are used to operating at that angle - and the angles change as the wheels go up and down

Looking at the pictures I don't think you will have enough space - unless you cut the BMW suspension arms and make them longer and move the beam they attach to forwards

OR - you may be able to put the Leaf unit in backwards


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## zippy500 (Apr 3, 2017)

Duncan said:


> OR - you may be able to put the Leaf unit in backwards


Think this discussion has been made in the past, that would be a ideal solution
I think the standard leaf invertor has limits about going in reverse.

Pauls controller will make the motor run at full speed in reverse, but the leaf gearbox isnt designed to run at speed in reverse.

I dont want to cut out the diff support beam in the boot to find it doesn't fit

Its not looking good at the moment


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## electro wrks (Mar 5, 2012)

Like Brian says, What I saw as a crack must be a slot in the mounting boss casting. Mounting this unit in the rear seems like a lot of trouble to go to because a suitable coupling can't be found for a bolt-to-the-transmission mounting. Has anyone come up with a coupling to fit the Leaf motor?


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## brian_ (Feb 7, 2017)

I think in this discussion we're seeing why there are only rare instances of an electric drive unit being mounted anywhere which wasn't originally an engine location. Those rare cases all include specific design features which are significantly different from the combination of a Leaf drive unit and semi-trailing arm suspension.



zippy500 said:


> I am planning to remove the whole boot floor area
> 
> I am thinking to cut and remove the cross beam that supports the diff at the moment.


That leads to substantial work to restore the structure of the rear of the car. Also, the suspension subframe needs that third mounting point to the car's structure.

Before cutting anything, it would make sense to me to unbolt the whole suspension from the car and set it up with the motor to see how it might fit together.



zippy500 said:


> Was even thinking of separating the invertor from the gearbox.


It's really separating the inverter from the motor, but okay...

While that's easier with the earlier style of Leaf drive unit (in which the parts are connected by external cables), it should be possible even with this later style to pull off the inverter and build some cables and seals for the terminal access openings to separate the components.



zippy500 said:


> One question. If i mount the gear box say 3" of centre from the drive shaft will the CV joints be OK with that or do they need to be in line?


As Duncan said, you can shift the drive unit (presumably rearward for more clearance to the suspension arms) so that the outputs are off line from the centre of halfshafts, within reason. Lots of production vehicles have an offset like this, usually because a rear-mounted engine is too long to fit otherwise. Watch lengths - you don't want a CV joint to hit its length limit and try to pull apart at full suspension compression or extension.

You can also shift the whole drive unit sideways (to the left), putting it closer to the centre of the car, for better clearance to the right-side suspension parts. That means a longer axle shaft on the right side and a shorter one on the right side, but you're going to need custom shafts to connect the Leaf drive unit outputs to the BMW hubs anyway.

CanadaLT28 has the only combination of Leaf drive unit and semi-trailing arm suspension that I've seen, and to make it work he has the drive unit shifted to the left, relatively narrow suspension arms, and a wide vehicle.



zippy500 said:


> Only reason for this route is the ongoing issue with coupler for the leaf shaft, or I would go conventional route with mounting to the cars gearbox.


If you can fit the whole drive unit in the rear, you also remove the motor and transmission weight from the front (which is going to be heavy once it is stacked up with battery), and provide much more space in the front for battery (by getting the motor out of the engine compartment).


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## brian_ (Feb 7, 2017)

electro wrks said:


> Has anyone come up with a coupling to fit the Leaf motor?


It has been done, because I've seen photos of a Leaf motor mounted in place of the engine in a conventional longitudinal-engine car.


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## brian_ (Feb 7, 2017)

Duncan said:


> Looking at the pictures I don't think you will have enough space - unless you cut the BMW suspension arms and make them longer and move the beam they attach to forwards


I agree that space between the arms is a real problem, but both extending the arms and the related relocation of the subframe forward would have substantial consequences to suspension geometry and structure.

I think it would be more feasible to modify the suspension arms to narrow them, so that the inner pivot point is further outboard, leaving more room for the drive unit between them. Even that would require stiffer bushings and substantial structural re-working of the arms.


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## brian_ (Feb 7, 2017)

It might help to start with a chassis drawing such as this one, and see how the Leaf drive unit (and possibly the subframe) would fit into it - you have the drive unit so you can measure key dimensions.

2002-Chassis.jpg


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## zippy500 (Apr 3, 2017)

Thanks for feed back very informative. 

Had a quick look in the garage tonight, Think everyone's response is correct that the sub frame wont fit, I'm not even going to think about cutting and modifying the suspension arms.

Back to the drawing board, if you look at the leaf motor setup, there is no reason why the front engine mounting arms cannot be removed, they have a three bolt triangle setup.

Im sure with some 6mm steel plate, shorter mounting arms could be made. maybe even use different mounts, the middle part of the leaf mount has to be in the air.

had a rough measure up .I think that the width of the engine could be down to 26-28 inches.

Make a H frame engine cradle for the engine to fit. this is probably more like CanadaLT28 has done



brian_ said:


> If you can fit the whole drive unit in the rear, you also remove the motor and transmission weight from the front (which is going to be heavy once it is stacked up with battery), and provide much more space in the front for battery (by getting the motor out of the engine compartment).


My thought exactly, think of the weight and space saving by losing the whole original transmission setup


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## brian_ (Feb 7, 2017)

zippy500 said:


> Back to the drawing board, if you look at the leaf motor setup, there is no reason why the front engine mounting arms cannot be removed, they have a three bolt triangle setup.
> 
> Im sure with some 6mm steel plate, shorter mounting arms could be made. maybe even use different mounts, the middle part of the leaf mount has to be in the air.


I do see how the two mounting brackets that are visible in the photo are bolted on, and I assume that the other is similar. Different brackets could certainly be used, as long as sufficient distance is maintained between them (for stability) and room is left for the rubber isolators.



zippy500 said:


> had a rough measure up .I think that the width of the engine could be down to 26-28 inches.
> 
> Make a H frame engine cradle for the engine to fit. this is probably more like CanadaLT28 has done


Great, but if you look at CanadaLT28's setup the whole width of the drive unit is between the inner ends of the suspension arms. Looking at the BMW chassis, the distance between the arms is barely more than the width of the final drive housing... not nearly wide enough for the Leaf gear. It works for CanadaLT28, because he has a wider vehicle, and probably narrower suspension arms.


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## CanadaLT28 (Oct 15, 2011)

I don't have a great pic showing my setup so I'll take a better picture tomorrow. Not sure if it will help at all as it looks like yours will have to be quite different.


I'm still interested in the motor coupler if anyone has a pic or a product to look at.


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## zippy500 (Apr 3, 2017)

CanadaLT28 said:


> I don't have a great pic showing my setup so I'll take a better picture tomorrow.


Have you made engine mounts or is the engine sitting in the air


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## Duncan (Dec 8, 2008)

My tuppence worth on this

As somebody who put a Lancia engine and gearbox in a mini - don't worry too much!

If that was mine I would unbolt the entire BMW rear suspension and throw it away - treat the mountings for it as "hard points" to which I would bolt the Leaf subframe

I'm pretty sure the leaf subframe will include the mounting points for the leaf bottom arms - if you use them then all you need to do is to beef up some strut top mountings 

Then you will end up with strut suspension in the rear - which works pretty well


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## CanadaLT28 (Oct 15, 2011)

zippy500 said:


> Have you made engine mounts or is the engine sitting in the air



In the pic you can see some threaded rod and the frame hangs from these. The mounts are made to fit the Nissan motor mounts (which is a pain to make so I would suggest to use the Nissan frame if you can), so yes, it is sitting in the air. I am waiting for some brake parts to show up then I will load the suspension up and set the lengths for the half shafts and weld them up. Then on to the battery system.


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## electro wrks (Mar 5, 2012)

CanadaLT28 said:


> In the pic you can see some threaded rod and the frame hangs from these. The mounts are made to fit the Nissan motor mounts (which is a pain to make so I would suggest to use the Nissan frame if you can)


Ditto on this. Even if you eventually end up cutting away most of the frame, it will much easier to adjust the set-up and tack weld to the steel frame.


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## brian_ (Feb 7, 2017)

Duncan said:


> ... If that was mine I would unbolt the entire BMW rear suspension and throw it away - treat the mountings for it as "hard points" to which I would bolt the Leaf subframe
> 
> I'm pretty sure the leaf subframe will include the mounting points for the leaf bottom arms - if you use them then all you need to do is to beef up some strut top mountings
> 
> Then you will end up with strut suspension in the rear - which works pretty well


That would work; the lower control arm mounting points are visible on the subframe. Track rods (like steering tie rod ends, but anchored to fixed points) would also be required.

Of course, most of the structure in the vicinity of the rear axle would be cut out of the car to fit the drive unit and subframe (including the structure supporting the BMW's rear suspension subframe mounting points), the forward Leaf subframe mounts would not likely coincide exactly with the BMW subframe mounts, and there would be no existing structure coinciding with the rearward Leaf subframe mounts, so there would be a lot more work than just "beefing up" the strut top mounting points (which also won't line up with the BMW's spring perches).

The closest to this scenario that I have seen in a recent DIY Electric Car project is the complete Tesla Model S rear subframe (with drive unit and suspension) installed under the back of a Nissan Skyline: _Tesla Powered Nissan r32 skyline_. That builder (Chris) gave up on making the Tesla drive unit work with the Skyline's rear suspension, so he did the more extensive transplant. The Skyline has a bulkier stock rear suspension than this BMW, but Chris still had to cut into the trunk, and build an extensive mounting frame; the car is not for street use, so it didn't need to be practical. Of course, this is a different model of car and different drive unit and different type of suspension, so all of the details of fit and installation are different.


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## Evbeddy (Jan 5, 2020)

Hi guys

I know this thread is a couple of years old but it is interesting and still relevant I think. 




Duncan said:


> ....treat the mountings for it as "hard points" to which I would bolt the Leaf subframe
> 
> I'm pretty sure the leaf subframe will include the mounting points for the leaf bottom arms - if you use them then all you need to do is to beef up some strut top mountings
> 
> Then you will end up with strut suspension in the rear - which works pretty well



Do you think this approach would work on a vehicle with leaf springs as rear suspension? Get rid of the diff and leaf springs. Fabricate up points to take the leaf subframe off the old suspension points or the chassis rails, and reinforce the top of the wheel wells to make strut towers.
Mount the leaf motor and transaxle in the subframe and mount the inverter separately. 

What are peoples thoughts?


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## brian_ (Feb 7, 2017)

Evbeddy said:


> Do you think this approach would work on a vehicle with leaf springs as rear suspension? Get rid of the diff and leaf springs. Fabricate up points to take the leaf subframe off the old suspension points or the chassis rails, and reinforce the top of the wheel wells to make strut towers.


That's get rid of the entire axle, not just the diff.

This might work better than starting with many independent rear suspension cars, because the leaf spring mounting points to the structure are sort of generally closer to where support is needed for the Leaf subframe... 2 ahead of the axle line, and two behind. 

Those strut towers are needed, and take the entire axle load; another challenge is that the distance between front and rear leaf spring hangers (determined by the leaf spring length) is likely longer than the distance between the front and back mounts of the Leaf subframe. To handle both of these issues, some sort of truss structure spanning the leaf spring mounts, picking up the subframe mounts, and carrying the load from the strut down to the spring mounts would probably be suitable. Side-to-side distances won't likely happen to match up, so some crossmembers or other lateral structure would also likely be required.


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## Evbeddy (Jan 5, 2020)

Thanks Brian,
I agree with your thoughts. Its good to bounce ideas offknowledgeable people tho. Time to go search the local wreakers for crashed leafs.... 😀


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