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Discussion Starter #1
I have a good basic understanding of how the mechanical "on-demand" CRV awd system works, and it's operation seems very straightforward and it's simplicity provides reliability. I have always wondered however, that there must be some amount of "overlap" available to the rear wheels before the drive disengages to prevent it from "hunting" on slippery surfaces. For example, in snow or on ice if the front wheels slip the difference in speed between front and back causes the rear differential pump to engage the clutch pack providing torque to the rear wheels. As the rear drive kicks in, providing they have sufficient traction, the vehicle begins moving and the difference in speed between front and rear decreases and the clutch pack disengages. If the clutch pump were to disengage quickly the vehicle may still be in position to be slipping at the front end, causing the cycle to repeat continuously until front traction is sufficient to eliminate wheel spin. It seems like this would result in the rear end constantly kicking in and out, but I've never noticed that occur. So, there must be some kind of pressure regulator that allows the rear drive to kick in quickly when needed, but release more slowly in order to "test the waters" as it were and keep things from rapid cycling.

Is that fairly accurate?

Also, I've been perfectly content with this system and it's never let me down, so need to bash it in comparison to other "better" methods.
 

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Everything in Moderation
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Yes, there is a engagement lag, I can feel it on one hilly traffic light in wet weather. I always get a little front wheelspin before the rear kicks in. (That's what I get for trying to beat the opposing traffic on the left turn) :)

Realize that the system will never 'kick in and out' as you describe, because the engagement is much more slow acting than what you envision. In fact on the newest CR-Vs an electric clutch engages the rear wheels from a stop, to speed up the traction process a bit.

Apparently, the pumps create a bit of heat, so there is a relief valve that dis-engages the rear diff after a long period of engagement.


So, stop showing off with all those donuts, OK?
 

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Discussion Starter #3
Sounds like I had the right concept, just the other way around in that the engagement is slower than disengagement. Which makes sense in hindsight. Thx.
 
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