Fabrication and suspension challenge: how would you mount this "big diff"?

jokeitch

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Jul 25, 2019
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i made an identical thread on the corvette forum, not sure how you guys feel about them, but i imagine i could get some additional info here.

Here's a real challenge for those of you into heavy fabrication and making your own suspension geometry.


how do you make THIS (top of the pic is towards the REAR of the car)


model-3-drivetrain-1.jpg

$_1.jpg

LIKE-NEW-Tesla-Model-3-Rear-Drive-Unit.jpg


Fit into THIS, replacing the stock diff and half shafts?

suspen1.jpg



it's the rear drive unit of a tesla model 3
more visual reference from the under frame of a model 3 (skip to 1:56) https://youtu.be/bkg0xcCanZs?t=114

For visual context, the drive unit has its own built in diff, essentially, and the half shafts exit from that narrower portion towards the "Rear" of the drive unit. I believe orientation is relevant because if you flip the unit 180, the left and right wheels are essentially reversed, or "reverse" becomes your forward direction, etc. Shape wise, it's a T much like a normal diff, but flipped with the long axis of the T facing towards the back of the car.

The drive unit cannot be a structural member, so bolting directly into it like the leaf spring does with the diff isn't an option.
Also because the drive unit weighs like 275 pounds on its own, the leaf spring will have to go, and whatever coilover system replaces it will need some strong springs.

will it be a matter of essentially creating a subframe assembly from scratch, with mounting points for those bushings on the drive unit, and places for the IRS to bolt to?
transferring the entire model 3 subframe over won't really work, the track width is too narrow for the c3. (62.2" instead of 69")
I imagine cutting into the underside of the body is inevitable....

An alternate approach is to literally take that entire rear subframe and mod the c3 frame such that it bolts up, welding some additional members to the c3 frame where needed. My concern with that approach is needing to add shock towers and spring perches onto the c3 frame in geometries identical to the model 3's, and i have no idea how easy/hard that is to do on a c3. Also the model 3's track is 3" narrower on either side, this might not be that hard to fix, any model 3 wide body mods will involve widening the track anyway, i can just duplicate that.

Yes, this is an Ev conversion plan, but before you scoff at the idea of an electric C3, remember that with software unlocks and enough amps delivered, these suckers can potentially smash out 500 wheel horses with instant throttle response, the torque curve is completely flat, and a "full tank" costs $10 instead of $80 in California here
 
more info: the shock and spring placement at the rear is a little funky, here's what i could find

ss-Steel-Sport-Brake-Line-Set-for-Tesla-Model-3_03.jpg

tesla-model-3-rear-wheel-well-covers-missing-clips.jpg
 
As mentioned above by Kacyc3, SBG's work. And, if it was me I'd use as much Tesla suspension as possible. Wheel offset might be enough to get the right track width. If not mfain posted photos of his work on extending a arms.

Relocating the battery and hacking out the rear compartments isn't too hard. I did that for big half shafts.
 
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I read the Model 3 track width is a bit over 62 inches. So I'd make a sub-frame, cut up the inside as mentioned, then use all the Tesla gear, and add flares. You'll maybe want to go wider than the 8.5 rear wheel anyway.

You'll not be "fooling" anybody with the exhaust "note.":trumpet:

Cheers - Jim
 
Why make a new subframe? the image i posted first is the entire model 3 subframe, i was going to just weld in mounting points for that entire subframe to bolt in as if it's in a model 3

no idea if it's going to collide with the stock c3 frame though, but it being narrower helps in that case
 
Why make a new subframe? the image i posted first is the entire model 3 subframe, i was going to just weld in mounting points for that entire subframe to bolt in as if it's in a model 3

no idea if it's going to collide with the stock c3 frame though, but it being narrower helps in that case

If thats the full sub frame I would look to see how much of it can replace the vette frame hopefully making the car lighter and reattach the body mounts to the new frame.
 
If thats the full sub frame I would look to see how much of it can replace the vette frame hopefully making the car lighter and reattach the body mounts to the new frame.

oh! like completely chop the stock rear frame and weld this guy in its place? Hmm, an interesting thought.....

although, those subframe bushings are probably there for a reason, if i hard weld all that in place, might cause some badness.
i guess it all depends on how things line up when they're in the car
 
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oh! like completely chop the stock rear frame and weld this guy in its place? Hmm, an interesting thought.....

That is what I meant to say. [Didn't do a very good job of it.]:eek:

I was suggesting; create a frame "section" that mates to all the Tesla bits, and then weld it to the C3 frame.
I did a pretty radical frame-ectomy of the rear section on my C3. I "think" it made the mods I did easier. [Inboard brakes, raised diff, complete setup of control arms - eliminated the trailing arm set up.]

Look forward to following this build.

Cheers - Jim
 
you asked my opinion....

I think you would be far better adapting the entire sub-section from the Tesla into the Corvette. The first problem with 'just' replacing the center section is the driveshaft on a C3 is the upper control arm - because that unit is so much wider, shortening the driveshafts would give you a lot of camber gain through the suspension and make it feel like you're driving on ice... shifting ice.

nice part about it being a subsection is the handling has been worked out and design compromises (short upper arms) I'm sure have been addressed - though now you make me want to run a Tesla down a dirt road and see what happens (not much travel)....

and still.... cool concept, the devil will be in the details - and the other detail, the short travel suspension could make you need to change or limit the front suspension .... I'd be interested to see its design as well...
 
by driveshaft do you mean the half shafts? there is no driveshaft with this tesla motor setup, the entire motor and inverter and gearbox is that big silver thing, half shafts come out the side to the wheels

although i think you're agreeing with the notion of taking the entire subframe and bolting it to the c3 ladder frame? I'm definitely going to be doing that now instead of my previous plan
 
by driveshaft do you mean the half shafts? there is no driveshaft with this tesla motor setup, the entire motor and inverter and gearbox is that big silver thing, half shafts come out the side to the wheels

although i think you're agreeing with the notion of taking the entire subframe and bolting it to the c3 ladder frame? I'm definitely going to be doing that now instead of my previous plan

Yes he did but, he was referring to them on the c3 suspension and the complications that would ensue if you tried to graft the C3 and Tesla suspension together. Where as the new plan will simplify it.
 
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