2wd ICE to 4wd Hybrid conversion question

This is something I'm considering myself.

After much pondering, I think the easiest approach, both legally* and in terms of engineering, would be start with a 4WD vehicle, or one that comes in both a 2WD and a 4WD version (Toyota Hilux, Rav 4, or one of the mini SUV / crossovers).

Starting from a 4WD: disconnect the ICE from the rear wheels, now it's front wheel drive. Then connect your electric motor to the rear diff.

Same in principle if you're starting with a 2WD version. A FWD ICE would be easiest to convert - find a driven rear axle to suit, preferably from the 4WD model of the same car, attach e-motor to diff.

If your donor is a front engine RWD, your engineering is going to be a bit more complex: you'll either have to e-drive the steerable front wheels, or find a front wheel drive rig to bolt up to the existing ICE, drop the main driveshaft, electrify the rear as above.

Overall I think starting from a vehicle that's already 4WD is going to be the simplest approach.

Dropping the drive shaft/s and transfer case/s between the front and rear axles will gain you a little weight to use for batteries, e-motor, etc.

What you want is doable, for a price. Is it practical, viable, or the best approach? Well, that, I'm still pondering myself, so I can't say, but there's no reason you shouldn't investigate it further.

For example, I'm looking at converting a 4.5 ton truck** to all-wheel drive as an expedition vehicle. That's gonna be expensive whatever approach I take, so I'm not ruling out electric drive at this stage.

Good luck.


[* Where I live, the laws on modified vehicles are pretty strict. YMMV.]
[** Daihatsu Delta, a badge clone of the Toyota Dyna. A cab-forward heavy pickup, front engine rear wheel drive]

Yes, you can be pulled over and defected, if you're unlucky - and then you'll be off the road until you can make it legal.

The major effect of any illegal mods is that you won't be covered by insurance (which is a compulsory annual purchase) if you get into an accident. So if you slam into a Rolls Royce you'll end up paying for all their repairs out of pocket - even if they're at fault. And your own repairs, and then you'll have to make it fully compliant anyway ($$$) before you can get it on the road again.

So the standard procedure here is to talk to a licensed engineer from the beginning of the project. They have to inspect and sign off on all work and provide documentation to the state authority anyway, and if you DIY and mess it up, you'll end up paying them twice to fix it. And there's only about a dozen workshops in my state licensed for that level of work.

There are some mods you can DIY without an engineer, but they're mostly fairly minor ones. Converting a 2WD to 4WD would count as a major mod.