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Rear subframe conversion ruminations

5111 Views 83 Replies 10 Participants Last post by  Duncan
Cars with live rear axles make for frustrating conversions, mainly because you have to keep a manual transmission up front. Adapter is a grand or two, and the 2:1 TorqueBox is $4k (plus custom driveshaft). If you ditch the axle, you have to reengineer the suspension, which involves much more than cutting and welding.

Enter the rear subframe swap. Many conversions will take a Tesla subframe and stuff it in the rear. The difficulty here is that Teslas are wide, and many of the cars I'd like to convert are narrow. It also makes using different wheels tricky.

Has anyone successfully gotten an electric motor and gearbox into something like a Miata rear subframe? E30? What are some other rear subframes that are narrow with pickup points that a Leaf/Tesla motor could bolt into without moving the suspension pickup points?

What are the implications of changing the rear suspension geometry and travel while keeping the front stock? For a sportscar it would make me nervous, but for a daily driver or cruiser...not so much—just get over these bumps!

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A remarkably spacious RX7 rear subframe:



Sure seems like you could just bolt this thing into a reinforced rear and roll along...

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E30 has another spacious trailing arm setup...Track width is 56" (though I think I really want the hub face to hub face measurement):

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How would that be superior to a Leaf with a TorqueBox?
Welding up shock mounts to the frame or subframe seems straightforward as long as the angle is reasonably close to stock and there is no interference through travel. Probably involves cutting into a trunk, but that seems like a given for the rear-subframe approach.

Doesn't the Tesla inverter bolt off, or does that let the fluid out? It wouldn't be hard to rig up some wires for a "remote" inverter.
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"Track width" does seem to be an ambiguous term, and the real measurement we would want (to avoid wheel offsets) would be hub face to hub face.

Many of the cars I've thought about converting are old RWD cars with solid axles, and this decision comes up every time...Right now, I'm thinking mostly about a 1951 Studebaker Champion, which is body-on-frame.
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It's not clear to me how you can keep suspension points on the solid axle when moving to a dedion setup...Cut the axle inward of the spring mounts, and weld the dedion bit? I think the axles would hit the tube at certain angles if the motor wasn't bolted to the dedion tube...I guess it depends on how much clearance there is inside the part of the axle...
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It just seems harder than getting a subframe in.
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I think we've gone a bit too far into the weeds here—the point of this thread is specifically to avoid re-engineering suspensions. Let's stay focused on subframes that would be advantageous for EV swaps into narrow RWD cars.
On our Mazda RX-8 rear subframe conversion, we didn't modify the chassis at all, but we did modify the heck out of the subframe.
Do you happen to have any before/after shots? I'd love to know what was really involved. Hopefully you didn't have to change the suspension connection points.
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