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Old 07-25-2019, 08:00 PM
jokeitch jokeitch is offline
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Default Fabrication and suspension challenge: how would you mount this "big diff"?

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)









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





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) [Only registered and activated users can see links. Click Here To Register...]

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
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Old 07-25-2019, 08:01 PM
jokeitch jokeitch is offline
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more info: the shock and spring placement at the rear is a little funky, here's what i could find



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Old 07-26-2019, 01:40 PM
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Old 07-26-2019, 04:25 PM
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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.

Last edited by rtj; 07-26-2019 at 04:32 PM..
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Old 07-26-2019, 07:20 PM
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phantomjock phantomjock is offline
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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."

Cheers - Jim
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Old 07-26-2019, 07:52 PM
jokeitch jokeitch is offline
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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
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Old 07-26-2019, 07:54 PM
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Quote:
Originally Posted by jokeitch View Post
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.
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Old 07-26-2019, 08:41 PM
jokeitch jokeitch is offline
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Quote:
Originally Posted by Kacyc3 View Post

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

Last edited by jokeitch; 07-26-2019 at 09:26 PM..
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Old 07-26-2019, 09:51 PM
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Quote:
Originally Posted by jokeitch View Post

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.]

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
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Old 07-27-2019, 08:31 PM
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Looks like a pretty well packaged unit. Are you doing the AWD?

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