[Maverick 44]

Dear DIY ECar Community,

I have been slowly working on my Tesla LDU - C3 Corvette since early this year. My plan is to swap out the rear end, use the Daimen board as motor controller, make a battery box in the front where the engine and transmission used to be, and make a custom control panel in the dash for all the new electronics. Goal is to have this up and running as barebone with 150mil range in 2 years time. I am not making a race car for the track, I just want to build my dream car with electric and I think anything less than a Tesla LDU will be an insult to this beautiful body!
Something like this:

I also have to mention that I only have novel experience on fixing cars, you know like changing oil, sparks plug, mostly hardware... I work on some electronics before like soldering components on circuit boards and troublshooting with a multi-meter. I am pretty hands on so I think I can do it with the DIY & Youtube community (like Electric Supercar & Roadcycler).
So, I started with a CAD drawing match up of the frame with the Tesla Model-S subframe. Looks like its not to far apart, need to relocate a cross member and make a few mounting points and the real thing is pretty close.

Next on the list is suspension, plan:

• Model-S width ~77" and the C3 is 69", this thing is going to be a wide body, which is what I like anyway. And I would like to lower it by a couple of inches too.
• tires: copy C6 corvette, F: 245/40R18, R: 285/35R19
• coilover for front and back, likely QA1s, adjustable, because I have no idea where the final height is going to be.
• need custom shock mounts for the rear, and this is the part I will need help on.
• totally no idea on the spring rate... for what I gathered on weight:

Factory C3 front ~1750lb, rear~1782lb (3550lb total). Engine and Trans ~650lb
If I swap out the Engine+Trans and replace with 14 Tesla battery module (~1000lb), the car would be ~4000lb.
Front spring like 550lb? rear like 350lb?
- I need to figure out what spring rate I should use for the coilovers... help!!!

I also need to figure out where to weld on the rear suspension mount on the frame.

I have a cardboard cut out of the wheel well space available, and with a paper roll I can estimate that I barely have the space for a 12 inch shock. However, because there is no weight on the suspension, it is very difficult to tell where the "natural" position of the wheel / rotor going to be for me to decide on a ride height.
For those who have done a Tesla LDU swap, what shock / spring / combination did you use? I really need some help to get the right shock / spring combo to begin with.

Thanks in advance!

Mike

 

[ev-swap]

Hi Mike,
What an exciting project! I love the look of the C3.
As a kinda/sorta answer to your question about coil overs, have you considered using rockers and mounting the coil overs horizontally? That solves your short height problem (12.5 inches) and allows you a lot of room to play with different coil over lengths and spring rates once you get the batteries installed. There is a guy converting a 72 plymouth Satellite and has the same issue as you. With these older suspensions that used trailing arms and springs, there just isn't much room for a vertically mounted coil over. (I know your C3 uses a horizontal leaf spring instead of coil springs, but the space challenge is the same. So they guy went the rocker route. If you watch his youtube videos, he does a great job of documenting how he built the rear coilover system. Check it out and keep us posted!

Mike

1972 Plymouth Satellite with a Tesla Model S Motor – Engine Swap Depot

engineswapdepot.com

 

[MattsAwesomeStuff]

I missed this somehow from earlier.

Your work looks great.

I haven't seen a lot of people doing suspension modifications on their vehicles around here, so, might not be the best place for advice.

Please keep us posted!

 

[Maverick 44]

Hi Mike,
What an exciting project! I love the look of the C3.
As a kinda/sorta answer to your question about coil overs, have you considered using rockers and mounting the coil overs horizontally? That solves your short height problem (12.5 inches) and allows you a lot of room to play with different coil over lengths and spring rates once you get the batteries installed. There is a guy converting a 72 plymouth Satellite and has the same issue as you. With these older suspensions that used trailing arms and springs, there just isn't much room for a vertically mounted coil over. (I know your C3 uses a horizontal leaf spring instead of coil springs, but the space challenge is the same. So they guy went the rocker route. If you watch his youtube videos, he does a great job of documenting how he built the rear coilover system. Check it out and keep us posted!

Mike

1972 Plymouth Satellite with a Tesla Model S Motor – Engine Swap Depot

engineswapdepot.com

Thank you Mike, I got the 12inch coilovers from QA1 and a bracket from Ridetech, looks like it may work. The rocker idea is interesting, but will need more work and more room inside the car. I will update later when I got the shocks install. More work on getting a set of wheels with correct offset not to obstruct the shock.

 

[DANTM]

Hi Maverick. I like the idea! Reminds me of starting my own project a couple of years ago only a C5. Looks like using the rear subframe is the way to go on a C3. Good Luck!
I also used the Tesla LDU but was able to separate it from the gearbox and mount it in the subframe. I made a long video if you have time. Search for "The Corsla" on you tube.

 

[Maverick 44]

Hello Dan, I saw your Youtube video. It was great. What a good idea to split the LDU into 2 and getting it fit onto the original subframe.
I finally got the suspension bracket welded in and powder coated the frame. I am going to need a wheel with an offset of ~22 to get enough clearance.

Got a question from your video: you mention you used the LG Chem battery and had to reconfigure the small battery packs' series / parallel combination to increase capacity. My understanding is that it will be fix, mixing the series / parallel can change the Voltage and Current, but capacity remain the same. Were you able to see the change?

You also mention you are in the LA area, I am in Ventura, just an hour North. If you don't mind, I may pay you a visit some day!

 

[DANTM]

Nice shocks. I have the same ones up front. As far as spring rate, as long as you have coilovers, you should be in good shape. Springs are easy to change out. For my battery pack I put two of the cells in parallel then put 96 in series. They were about 40-45 AH each so now I have about 80/90 AH cells. Parallel increases capacity with same voltage. BMS just thinks one cell is actually two cells in parallel.
Question, I know this is the least of your concerns right now, but how are you controlling the Tesla parking brakes?
I am located out near Murrieta. So a bit outside of the greater LA area to the East. Shoot me an IM if you want to meet up.

 

[Maverick 44]

I plan to use the e-brake controller by Pantera Electronics.

www.pantera-electronics.com/epbcontroller.htm

I saw this on Roadstercycler on Youtube.

 

[DANTM]

I plan to use the e-brake controller by Pantera Electronics.

www.pantera-electronics.com/epbcontroller.htm

I saw this on Roadstercycler on Youtube.

I figured. I fabricated a dropout to add Tesla Calipers on my rear hubs. Barely fit but the Pantera controller works great.

 

[kstegath]

I converted this C3 about ten-years ago.
1,200 lb of lead; 600lbs front, 600lbs rear. I used QA1 coil-overs in the front (QA now has springs that fit the upper spring pocket.)

Used lead-acid because it was much cheaper. And I wanted the challenge of cramming 24 batteries in a C3 Corvette.

The lead was dead so I started upgrading everything for racing.
But it didn't feel right hauling an electric race-car to the track with a diesel or gas truck;
So decided I needed to build an electric tow vehicle
This 1962 Mack B-46.

The Corvette and Mack are on hold because...
I got side tracked restoring and converting a clients 1976 Alfa Romeo Spider.

Flickr pics
Some more Corvette pics

 

[Maverick 44]

kstegath, that is really great! I saw your Yellow C3 on the web and just love it. One of reason I started my build.

Great to hear you are planning to upgrade the C3. What's your plan? be interested to hear and learn a bit more. I am in the research phase on the charging and battery system, so it will be great to know what experts are doing.

The Mack looks awesome, it will be quite a sight to see both together.

Its a funny thing you are working on an Alfa. I used to have a 82 Spider. It was a really fun car to drive. I was thinking to convert one when I am done with the C3, but my wife loves the Karmann Ghia, so it will be the VW next.

 

[dallas_]

Kstegaath, love the C3 conversion.
Maverick, I'll be watching your build. I think the C3 is a good option for a conversion. Looks like you're doing it the hard way.

 

[joekitch]

I was originally on the train of using the entire model s subframe but I've since been warned away from that by michael breme of ev west, who said, essentially;
"The model s rear is designed for an almost 5000 pound luxury sedan. Meanwhile, the c3 has a ton of aftermarket for rear suspension handling, and it's not that difficult to weld on some mount points for the model s motor"

So yeah that'll be my approach

That said, I wish I had your CAD and fabrication skills....

Are you going to scan or recreate the underbody fiberglass? It'd be worried about the motor slamming into stuff if all your modeling uses the frame only

 

[JJanavs]

I was originally on the train of using the entire model s subframe but I've since been warned away from that by michael breme of ev west, who said, essentially;
"The model s rear is designed for an almost 5000 pound luxury sedan. Meanwhile, the c3 has a ton of aftermarket for rear suspension handling, and it's not that difficult to weld on some mount points for the model s motor"

So yeah that'll be my approach

That said, I wish I had your CAD and fabrication skills....

Are you going to scan or recreate the underbody fiberglass? It'd be worried about the motor slamming into stuff if all your modeling uses the frame only

I'm in the middle of mounting a small Tesla rear drive in a C3 without the subframe. I dropped the leaf spring for a VanSteel coil over set up to make it an easier install and allow for ride height adjustment. The diff mount frame crossmember moved 4" back to be able to raise the motor up to align the Telsa diff as closely as possible to the original half shaft location. That made for a really short rear motor mount, with the front mount close to the original front differential mount. Working out that bracket and the side mount now. The biggest challenge may be the camber strut mount that will need to go under the tesla motor and mount to something...

 

[Maverick 44]

Hello Janvas,
Are you working on a C3 also? I do have to come up with my subframe mounting points. The ride height is a guess-estimate, especially with the coil over, very likely have to use an adjustable chamber link to get the alignment close. Send some pictures and we can trade notes on the project, still have a lot to do.

 

[brian_]

Hello Janvas,
Are you working on a C3 also?

Didn't he explicitly say that? Here:

I'm in the middle of mounting a small Tesla rear drive in a C3...

 

[brian_]

I do have to come up with my subframe mounting points. The ride height is a guess-estimate, especially with the coil over, very likely have to use an adjustable chamber link to get the alignment close.

Why is anything about the height uncertain? You know the height above ground of the frame and the hub centres in stock form, and there's no need to change that. The mount design then become an exercise in connecting the drive unit (at the height determined by the axle height) mounting points to the structure (at the stock height)... and moving bits of structure to avoid interference and finding a way to mount the inboard end of the suspension links as required, as JJanavs explained. Well that... and doing something about the axle shafts which are suspension links.

 

[brian_]

I was originally on the train of using the entire model s subframe but I've since been warned away from that by michael breme of ev west, who said, essentially;
"The model s rear is designed for an almost 5000 pound luxury sedan. Meanwhile, the c3 has a ton of aftermarket for rear suspension handling, and it's not that difficult to weld on some mount points for the model s motor"

That's valid, although the C3 rear suspension is a notoriously poor design. Fortunately, while it's not possible to make a silk purse out of a sow's ear, it is possible to make pretty nice leather purse.

But then there are the axle shafts...

I'm in the middle of mounting a small Tesla rear drive in a C3 without the subframe. I dropped the leaf spring for a VanSteel coil over set up to make it an easier install and allow for ride height adjustment. The diff mount frame crossmember moved 4" back to be able to raise the motor up to align the Telsa diff as closely as possible to the original half shaft location. That made for a really short rear motor mount, with the front mount close to the original front differential mount. Working out that bracket and the side mount now. The biggest challenge may be the camber strut mount that will need to go under the tesla motor and mount to something...

That all makes sense, but what about the axle shafts? In the C3 design, the axle shafts are suspension links, taking a large portion of the lateral force when cornering. This force is taken by the differential output bearings, something which the Tesla drive unit is not intended to do (no modern final drive or transaxle does this). Are you adding upper links to take this force (using axles with plunge as normal for modern vehicles), or are you using U-jointed axles and expecting the Tesla drive unit to take this force?

 

[Maverick 44]

Why is anything about the height uncertain? You know the height above ground of the frame and the hub centres in stock form, and there's no need to change that. The mount design then become an exercise in connecting the drive unit (at the height determined by the axle height) mounting points to the structure (at the stock height)... and moving bits of structure to avoid interference and finding a way to mount the inboard end of the suspension links as required, as JJanavs explained. Well that... and doing something about the axle shafts which are suspension links.

The ride height uncertainty is mainly from the difference I found in the CAD model I downloaded from the subframe and how to chose the rear coil-over spring force (the whole back end weight is different now and I don't even know what it would be...) and finally, I want to lower the car to have a more aggressive stance.

 

[Maverick 44]

That's valid, although the C3 rear suspension is a notoriously poor design. Fortunately, while it's not possible to make a silk purse out of a sow's ear, it is possible to make pretty nice leather purse.

But then there are the axle shafts...


That all makes sense, but what about the axle shafts? In the C3 design, the axle shafts are suspension links, taking a large portion of the lateral force when cornering. This force is taken by the differential output bearings, something which the Tesla drive unit is not intended to do (no modern final drive or transaxle does this). Are you adding upper links to take this force (using axles with plunge as normal for modern vehicles), or are you using U-jointed axles and expecting the Tesla drive unit to take this force?

My knowledge on handling is limited. I don't plan on taking the car to the track, just normal highway driving, doing anything the Model-S can do. So, I think installing the whole Model-S subframe with all the suspension is the best bet, there's shouldn't be too much difference besides the weight and distribution. Something similar to what Roadstercycle had done on his Tesla swap Mustang on Youtube did: (1) Roadstercycle - YouTube