AWD maintenance

You forgot to mention the most important detail. What transmission? The manual transmissions have a viscous coupled center differential. Maintenance would be changing the transmission fluid.

The auto trannies mostly use a transfer case with an electronically controlled clutch. I don't know if there's any particular maintenance you can really do for it other than tire rotations to keep the tires at the same circumference; the clutch can supposedly wear out early if the system senses a difference in wheel speeds all the time. The fluid in the front diff could be serviced though.

fluid changes in diffs couldnt hurt

If a difference in wheel speed due to tire sizes or other reason causes a problem then the car should be called a 4WD not an AWD.

If the systems 'interprets' slippage under conditions where no slippage can occur. It will 'switch' to (essentially) 4WD but be subjected to stress (torque bind) which COULD lead to failure of one or more driveline parts. The trick is to prevent conditions which 'trick' the system into engaging when it shouldn't. Running odd sized tires on dry/normal/hard road surfaces - particulary at high speeds for great distances - will likely stress the system. It MAY be possible to - say - put on one new tire with 3 older ones and run lower air pressure to compensate. But there would be safety issues with that I suppose.

Carl

I was always under the assumption that 4WD implied a 50/50 power split. Subaru AWD (automatics) have supposedly been anywhere from 90/10 to 60/40.

I have experience with 4WD but none with AWD. My personal criterion for 4WD is that the front and rear are hard-coupled, whether the front and rear differentials are locked or not. 4WD is the way to go in rough, demanding terrain but is a terror on slippery streets, since at least one wheel must give up traction to allow the vehicle to turn. In town I drive my 4WD work truck in 2WD even when the roads are icy because it gets squirrelly in 4WD (as I learned the hard way!) If the road gets really slippery and I have to get up a hill I'll change to 4WD, but chaining up is the proper way to go at that point..

Mike

well im not sure its official anywhere but usually the difference betweel full time 4wd and AWD is that AWD can handle different tires turning at different revolutions which happens during turning. 4WD does not account for/handle this.

The California Dept of Transportation seems to call any four- wheeled vehicle where are four wheels are driven "four wheel drive" for exceptions to chain requirements.

Certainly there's 4wd drive where the differentials can be locked in tough driving situations. However - most of these vehicles are driven in situations where there's power to all four wheels on pavement.

here's one explanation;

Carl