While spending far too many miles on the highway today in my Subaru, I had an idea:

 

The only thing preventing 4WD from being used on dry pavement is the fact that there's no center differential, and turning tends to bind up the drivetrain. I don't think there's an easy way to add a center differential, but having a driveshaft with a viscous coupling in it would have the same effect.

 

The reason for thinking about this is that my RX-7 has a wheel bearing going bad, I'm planning to autocross the GL wagon (should be interesting...), and 4WD would be incredibly useful for not spinning the tires coming out of a corner.

 

Has anyone else thought about this, or does anyone make one of these magical widgets? I'm thinking the turbo guys would find this useful as well.

 

-=Russ=-

look in the 4wd mags there is a company that makes a bolt on coupler that does just that for the bigger lifted chevy's ect with the full time transfercases

and way more hp than most of us have

so imagine it would not be hard to adapt

Just grab a driveline out of an "AWD" volvo. The AWD systems on them work just like the idea that you have. They have a fulltime 4wd gear box thats always feeding power to the rear output, then they have a viscouse couple just off the rear differential that takes up the slack, er, or lack of it anyways. What year did they start with the X720?(I tink), might be able to find one in a wrecking yard, it's been a little while.

My '89 Honda Civic 4wd wagon has a viscous coupler in the drive shaft.

The 4wd system is called RealTime, and I've seen that name on CRVs, etc. I suspect any Honda with RealTime on it would have one.