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Rear subframe conversion ruminations

5108 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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Check out this 300ZX build: 300ZX conversion for sale

Uses a LEAF transaxle inside the subframe. This is how I would do just about any RWD car. You can do the same with a Tesla DU.

Electrical wiring Automotive lighting Motor vehicle Gas Automotive tire
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I was going to link that one... thanks for catching it first.

This is the thread for the build: 300ZX Electric Conversion
The rear suspension is from the S platform, presumably the S13, so if the Leaf unit fits in this 300ZX it will also fit in the subframe (but perhaps requiring body modification) of the same-generation 240SX (for example), and a subframe from any of these models could also work for a Leaf drive unit in another vehicle.

Like most suspensions, the shock extends well above the top of the subframe, and mounts to the vehicle structure rather than the subframe. That's certainly a feature to consider in the potential use of any subframe in any vehicle. Fortunately, it's just a shock-mounted spring, not a MacPherson strut, so it doesn't serve a lateral locating function and takes only vertical force.
you can do it with many car's rear subframe. I'm guessing it would even fit in a Miata's subframe. The point is not to use a 300ZX subframe on a Miata lol.

Most Tesla drive units place the motor(s) behind the axle line, not ahead of it like the Leaf unit - that will certainly affect fit and required subframe modifications. The rear unit of the Model 3 and Model Y is the notable exception, with the motor ahead of the axle line.
Obviously it depends on how it's done and most does not mean all.
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Tremelune and others:

I'd like to learn more about these various suspension options, and how well they work with options like the Leaf motors, and the Tesla small motor. There are so many old rwd vehicles that could benefit from an upgrade, without having to go crazy on power. Personally, I don't know how to quantify what you could do with either of those options, trying to use OEM parts, and keeping it reliable and simple.

I don't think I've seen any posts about how reliable a Tesla small motor is, or comments about how you would repair the inverter if it fried. With Toyotas, Lexus, Nissan, Volt, etc there are plenty of options, but does that apply to Tesla?

I've seen posts where people talk about horsepower factors, sizing batteries, etc, but still have no way to judge what the overall experience would be like "in the real world" where most people rarely use much of the power that a typical ICE motor can provide. Is there a rule of thumb to determine if a Leaf (for example) could adequately power a Camaro, or a '51 Stude? I'm too old to be interested in little cars, so I'm much more interested in things I can actually get in and drive, load up some tools for a project, or just go cruising.
Just about all of the pony cars had hairdresser versions with anemic slant-6 engines or other boat anchors. You absolutely could put an undersized electric motor into a big car and cruise around. My truck weighs 5300lbs and my 80kw LEAF motor accelerates it the same as the stock 212hp gas engine.
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These are all helpful comments.

Remy/Duncan/Electric Land Cruiser: thanks for those comments. They help to frame some thoughts. I've got enough BMW modules sitting here on the shelf to reach that level, assuming a conversion weight around 3500# all in. Those modules are pretty heavy for their capacity, so I've been thinking more along the lines of using them in a project where the whole I3 battery would fit in the vehicle as is, with a 2011 Leaf setup. Heating and cooling that battery might be an issue, although it would be strictly for around town errands, no hills, range not a big deal.

I've been reading up on the Open Inverter forums to get a handle on the latest with the small Tesla (front) motor, and the gs450h for a pony car. Both of those are available to me right now, within driving distance. I watch Damiens videos for updates, and it appears that parts are starting to become available again, and various people are working out bugs. The gs450h would by far be the easiest, and it is actually smaller than my existing automatic. So the decision is which project to do. I don't have time to tackle 2. The Leaf project would be more work than the pony car, and in the end, would be worth squat. But fun, and usable, and I have most of the stuff now. The pony car, especially with a GS450h, would look stock except when you lift the hood. Lots of room in that engine compartment for batteries and inverters. The pony car would not be driven in winter.

A quick comment on the Tesla sdu...putting it in a rear IRS cradle would allow me to do that work outside the pony car, test it, and make minimal changes to the car. It would weigh more than the existing live axle, but would actually match or exceed the original V8 power. It would get rid of the drum brakes, but likely extend up into the trunk area. I like what I read this past week about splitting the inverter off that unit, and mounting it separately.

Fun stuff!
This is like the coolest car ever if you want some inspiration: The Story of Kevin Erickson’s 1972 Plymouth “Electrolite”, a Tesla Swap Done Right
Panhard rods are sometimes used with leaf springs, normally for higher lateral stiffness, and only when suspension travel is relatively short. This is the sort of thing usually found on race-prepared production cars from decades ago (such as the early 1970's Datsun a friend of mine had, which was race-prepared around 1980), not anything in street use and not anything recent at all.
That's not true. My Land Cruiser has a panhard bar and it has tons of suspension travel. A brand new 2023 Land Cruiser also has them. Most all 4x4s with solid axles have them from the factory.

Also Camaros and Mustangs from the 2000s. Crown Vic. Etc. Tons of cars have them and modern cars too.
There are no modern cars with beam axles and leaf springs. There are many trucks (light and medium duty) with basic beam axle and leaf spring suspensions, but they don't have Panhard/track rods or Watts linkages... just look at any pickup truck or van (such as the Tacoma).
Tacoma, 4Runner, Sequoia, etc all had panhard bars at least until 2016. Ford Bronco, Chevys, Ram. Practically every truck has them.
Those vehicles have coil springs and control arms, not leaf springs, except the Tacoma (which doesn't have a Panhard rod). Here's your 80-series, with visible rear coil springs, no leaf springs... and yes, a Panhard rod. Did you just not notice that we're talking specifically about the use of a Panhard rod with leaf springs?

That includes GM full-size SUVs with beam axles (Yukon, Tahoe, etc) and even Ram light-duty pickups. "Practically every truck" would be only Ram trucks and the 2023 Tundra, because they're the only ones with coil springs. While a Tahoe had (until it went IRS) a rear beam axle with coil springs and links including a Panhard rod, but the Silverado of the same platform series has leaf springs... and no Panhard rod.

Of course a lateral location function (Panhard/track rod, or Watts linkage, or angled upper arms, or upper A-arm) is required with coil springs.
Actually, you wrote a couple run-on sentences that could be interpreted in a few different ways. I'll let you have the win because I'm busy. I'm on another adventure with my DIY Electric Car. Much more fun than talking on the internet!
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