TRX wrote:
I never found any combination of reasonably-available transfer case bits that would work.
That is very true.
Most simple primitive off road transfer cases either lock the front and rear tail shafts together (solid), or have some type of centre differential that splits torque evenly front/rear 50/50.
There are also now available a vast number of ingenious schemes using viscous couplings, clutches, even active computer control. But they mostly all have characteristics sending most of the torque to the wrong end for a rear mid engined 4Wd road car.
My own preference is for an epicyclic torque splitter that is biased towards the rear, maybe 32/68 F/R.
This system is used by BMW, Jaguar, Hummer, and (in Australia) by GMH.
The transfer case I am using is the New Process 124 which is gear drive 32/68 split, without a low range.
This is ideal for a front mid engined car, but would not work with a rear mid engined car.
The only way I can think of doing a rear mid engined car, would be to use one of the primitive fully locked up transfer cases, and fitting a clutch between the front driveshaft and the front diff.
The rear diff of the very common Honda CRV already has such a clutch fitted within the diff housing.
And there are other very similar systems used on less common vehicles.
http://www.awdwiki.com/en/honda/ I have not really looked into this idea in any real depth, as my own mid engine 4Wd project has the engine at the front, which is a lot easier to do.
I am just thinking and mumbling out loud here, but the above 4WD link is full of ideas and some really interesting hardware.
Click on the topics listed at the left hand side of the above 4WD Wiki link, there is some really interesting hardware around if you are prepared to search it out.