1974 BMW CSE

JetDexter

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Here's another post from the BMWCSE.com Blog...

Junk in the Trunk

While all of that sunroof work was being done Brett and I started to have some fun with the Tesla drive unit.

For the uninitiated, many electric car conversions use a low-voltage DC motor in the engine compartment which connects to the car’s transmission. This is a clean and simple approach if your primary goal is to go electric. Generally these modest motors require the user to start in 2nd gear, then shift to a higher gear for highway speeds. This concept will successfully and affordably convert your slow gas-burning car to a slow emissions-free car. As a Tesla driver I had gotten hooked on the high-power, monster torque and overall performance they brought to the table.

The Tesla drive unit contains a high-voltage AC Motor, gearing, differential and electronics. It is placed between the rear wheels where a traditional differential would sit. This single unit will replace our engine, transmission, drive shaft and differential. At 291lbs it is a serious beast. We are hoping to maintain the original weight distribution of the car. While this unit is a tad heavier than the combined weight our old differential, full fuel tank and spare tire, the weight will be contained much closer to the rear wheels. Far less weight will suspended at the very back of the car.

We are not the first people to retrofit a Tesla unit into another car. We leveraged some of the engineering, trial/errors and successes from some of the more graceful projects that we have followed.


We started by clearing out the trunk floor. We want the motor to sit no lower than the original differential, but also no higher than necessary - leaving us with a good amount of trunk space.

Getting off the Ground

Our Tesla unit weighs 291 pounds, so I can’t exactly hold it in place while Brett bolts it to the car. We welded up a rolling stand that could safely hold the unit under the car, then we would use the car lift to lower the coupe to the unit.

Here’s our Tesla motor stand. I am going to reach out to Elon to see if he wants to put an order in for several:)


A forklift is the closest thing we have to an engine hoist, so here we go.


The unit feels secure in its temporary home.

Reinforce and Fabricate


With the unit on the rolling stand we put it into position to verify our mounting design and overall clearances. We strapped the rear wheel into a relative ride height, so that we could check the axle angles.

While we had done our homework I am not going to lie - there was some relief when everything fit without obstructions. Regarding the mounts: There is a front mount which was a simple matter. The side mount can be tricky since there is suspension right there, and the rear mount has nothing to hang from.


We plated the front and rear of the wheel well to distribute the loads and to give us something to attach to.


Brett welds in the horizontal plating, which will support our front mount.

The Front Mount

Cutting the thick stuff is like cutting warm butter when you have a plasma torch.


The front mount had the trickiest shape to it and required some bending of the center plate.


The front mount welded into the car.

The Side Mount

We created a side mount plate with a compound bend by notching, then smoothing out.


Welding the side mount sections to our plate.

The Rear Mount

The rear mount suspends from a beam which spans between the wheel wells.


Reinforcing the hanging points with gussets. It was just an opportunity to take a photo through the taillight hole.

Clean Things up and Hang the Unit

With the welding done, we cleaned up any rough edges and applied etching primer to everything.

The moment of truth...


Finally the drive unit is hanging in it’s final home! We strapped the front of the car down to the lift just in case things got a little back-heavy:)


The placement leaves plenty of usable trunk space. We have a large and deep rear section, then an upper forward shelf (with perhaps a plexiglass floor for any Cars & Coffee events we may find ourselves at). Next we connect the axles from the drive unit to the hubs. So that we don’t twist the old BMW axles we opted for Tesla performance axles, which will mate (somehow) to the BMW hubs.

That’s it for now- until next time!

Paul
 

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JetDexter

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We made a little more progress on metal the last few days.

We are going to tackle the rear portions of the rockers on both sides before we go up front. This is so that we can put our rear suspension back on as soon as we can. We need to have our Tesla axles modded up to drive the BMW hubs (we will certainly have an axle shop handle that). But we need to get the car sitting back on its own wheels to measure up and configure that.

We started in on the passenger side, because that is where the cutting torch was at the moment:) The rust damage was bad but not completely rotted, with rust only on the bottom of each layer. We decided to keep the good stuff and rebuild only the bad. Here's a before and after so far.

Rear-Rocker-Before.gif


Rear-Rocker-After.gif


The outer layer pieces are fabricated up, but we will coat this inside with some POR15 topcoat before we weld those on.

We also worked on the rear valance sections. We have a ways to go here, but it's getting close, and no need for an exhaust outlet notch :)

We used stock pieces for behind the wheels, and fabricated the rear section. Thought I was saving money over the $500 piece- but that compound bend probably cost us twice that in time, and it's still not quite there. Should have bought the piece. Here's a before and after so far...

Rear-Valance-Before.gif


Rear-Valance-After.gif
 

Gazz

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Have you considered the pendulum effect of that amount of weight in the rear? A la early Porsche. Being in line with the axles may mitigate the effect to some extent.
 

JetDexter

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Have you considered the pendulum effect of that amount of weight in the rear? A la early Porsche. Being in line with the axles may mitigate the effect to some extent.
Well, as you said, since that weight is tucked pretty tight up to the rear wheels it shouldn't be a bad effect. There will be 800lbs of batteries in the engine bay, so the 290lbs tucked behind the wheels should be insignificant. What is fun about Porsches (new or old- and the newer, the heavier back there) is just how light that front end is with only a fuel tank and spare tire. It is a literal miracle of engineering that they don't all do wheelies every time one takes off.
 

JetDexter

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A bit more progress today - of the controversial kind. We got our E46 steering column in.

Since this will be a daily driver, my goal is to modernize a few control elements. One example is a modern turn signal lever with lane change functionality. (not to mention it being on the correct side of the dang steering wheel) Also, I gain articulating adjustment. On top of all that, it weights less than half the original beast of a unit.

I will be fitting a Nardi wood wheel to it, so the look will be negligible other than the 2 levers.

Tomorrow an E46 brake pedal assembly will be fitted, along with the Tesla accelerator.

Steering-Column.gif
 

mane

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Nice! Maybe I should do the same :)

Are you doing rack and pinion steering rack too?

With lane change functionality, you mean triple blinking?
 

JetDexter

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Mane, I was saving the Rack and Pinion for a surprise. Mostly because I wanted to have it fully operational before posting about it in case we fail LOL.

But yes, for many reasons we are moving to a steering rack. Saving more weight (I think that a single one of the many vintage linkages weighs as much as our entire setup). But more importantly, we needed to gain the space. We now have a very compact setup allowing us to get more batteries in there.

We cut out all the motor and steering mounts and got the rack in yesterday. We still have to do some cleaning up in there.

My goal was to use 100% BMW parts for this project (or Tesla). But since modern BMW racks are front-steer, I had to expand my search to other brands. Because of the narrow track of the e9 (compared to even modern small cars) the VW MK3 GTI VR6 ZF rack seemed the best fit for us. The mounts are in a perfect spot and the front track is within a few millimeters.

For the record I would love an electric rack for the modern tech possibilities, but I wanted this car to feel as good to drive as possible, and this setup should provide a terrific feel. We need a 12v power steering pump anyway for our hydroboost brake booster, so that pump will provide power for both systems in a nice looped system.

The e9 steering arms will need to be modified to the shorter throw of modern setups. We have a plan for that...

Cutting-Mounts.gif

Steering Rack.JPG
 

mane

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Awesome stuff! I've been waiting for someone to point out something that fits relatively easy. No matter the brand. How did you find out that this VW GTI rack fits?

I also would have liked the electric rack, even though losing some road feel. Would be more simple setup without needing 12v hydraulic pump. My friend told me that it's okay to do the car without brake booster if brakes are proper. I'm bit skeptical about that.

I've driven Honda S2000 with electric rack, and that is awesome also in road feel. Very small too. Do you have the specs of the width etc for rack? I'd like to check that..

Having r&p give lot more room to batteries too. So good in many ways in these projects.

Keep us updated how it goes!
 

JetDexter

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More progress on rust this week. Tyler is an artist with steel. Rockers are getting very close. Here’s a before and after of the driver’s rear section.

I’m trying Tapatalk for photos uploading for the first time. Not sure I’m a fan as they are hosted with them, so one day they may disappear from here.






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JetDexter

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Today we got some rear floors in. Still have to clean up the driver side but the passengers side is done and we keep moving forward.




We are at the front section of the rockers and it is starting to get interesting up there.



Also, (and this one is not for the faint of heart) we finally have our power Rack & Pinion steering rack connected and once again have fully functioning steering. We have an E46 steering column connecting to a VW VR6 steering rack connected to our E9 steering arms. They connect much closer to the hub then the original location as modern cars do. There is a perfect flat spot to drill the new holes but for now we attached a plate to do some testing and it feels very good.






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JetDexter

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Started putting the rear end back together (temporarily so as to fit our axles and ultimately test drive train and such before paint). I opted for a Ground Control coilover setup. Those guys are great to work with and they sent me the rear-only for now since I can’t get them my strut inserts quite yet.

But they were as surprised as I was when the Koni lower mount insert was way too small. GC offers this E9 setup as a stock kit, but when I sent them this photo they said “that’s supposed to be a 10mm stud”.

I can’t imagine a smaller stud in this configuration. You guys have any thoughts?

Regardless they are going to rework the insert for me- thought I might just take a shot with my drill press. If it goes bad, I wouldn’t hurt the housing and they could still fit a new insert.





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eriknetherlands

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acc parts book it should be a M14 bolt, used '68 to '75. From memory that seems to be what I have on my car as well (I installed bilsteins ~2 years ago).
So if Koni's are designed to fit M10, then you'd be 4 mm off...

Knurled bolt
33 32 1 102 701
M14X70
 

JetDexter

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The Ground Control guys were great and already sent me the 14mm inserts for those shocks, so looking good there.

This week was spent mostly rebuilding the driver side rear fender. We crafted a new inner wheel arch, cut out rot- including rotted repair work:) and installed a new outer arch.

Everything is looking good now!




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