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Does the shaft turn when in FWD only? From a Press release:
System Layout
The Ridgeline AWD system is a fulltime system that requires no driver interaction or monitoring, thanks to a torque-transfer unit that is bolted directly to the front-mounted transaxle. The torque-transfer unit receives torque from a helical gear that is attached to the front differential's ring gear, and a short horizontal shaft and hypoid gear set within the torque-transfer unit's case send power to the rear propeller shaft, which in turn transfers power to the rear drive unit that has a 20-percent greater torque capacity.
Or does the shaft turn when the truck moves?
 

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Would be cool if there was a clutch designed to disengage the shaft and turn it into full time FWD however this is not the case and the shaft does turn when the vehicle moves. Fiat/Ram figured this out on the new Jeep Renegade 4x4 which does in fact disengage the rear axle to improve fuel economy.
 

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Would be cool if there was a clutch designed to disengage the shaft and turn it into full time FWD however this is not the case and the shaft does turn when the vehicle moves. Fiat/Ram figured this out on the new Jeep Renegade 4x4 which does in fact disengage the rear axle to improve fuel economy.
Having just come from a 2014 Cherokee Trailhawk to the RL, the system you describe is utilized on all FWD-biased 4X4 systems that Jeep/Fiat uses... Cherokee, Renegade and the redesigned Compass. The Grand Cherokee is a full-time AWD system.
 

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The shaft to the rear wheels turns whenever the vehicle is moving.

The rear drive shaft turns a ring gear in the rear unit, but there is no "differential" in it.

Drive to either rear wheel, or both rear wheels is done through a multi-disc clutch on each side of the ring gear. The stepper motors for each clutch control engagement pressure and therefore the amount of slippage, from some to none, independently on either or both sides, depending on orders from the powertrain computer.

In normal cruising, only the front wheels are driven. Wheelspin, hard acceleration or hard cornering will cause the rear unit to send power to either or both rear wheels as determined by the computer.

The control logic does not wait for wheelspin to drive the rear wheels on hard acceleration.
 
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If I understood his comment correctly, Joe has expressed concern about how those dual rear clutches will hold up over the long term because they will actually be in full slip mode for most of the time and miles the vehicle is moving. If there is a design weakness in the i-VTM4/SH-AWD(II) system, I would think it would show up first in 2016 MDXs and Pilots.
 

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If I understood his comment correctly, Joe has expressed concern about how those dual rear clutches will hold up over the long term because they will actually be in full slip mode for most of the time and miles the vehicle is moving. If there is a design weakness in the i-VTM4/SH-AWD(II) system, I would think it would show up first in 2016 MDXs and Pilots.
Yeah, I would not be concerned with the clutch life. They are actually fully disengaged for all but a very small fraction of driving conditions. The basic system design is over ten years old. The clutches themselves have been very robust. The very few problems reported with these systems seem to be in the actuators and electronic controls/wiring and a rare, occasional fluid leak.
 

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Yeah, I would not be concerned with the clutch life. They are actually fully disengaged for all but a very small fraction of driving conditions. The basic system design is over ten years old. The clutches themselves have been very robust. The very few problems reported with these systems seem to be in the actuators and electronic controls/wiring and a rare, occasional fluid leak.
The same design is in the Ford Focus RS, a performance car, or hot hatch. The 2.3L Turbocharged inline 4 in that car makes 350HP. GKN makes that system for Ford, and I know from Joe's posted supplier jpeg, that GKN makes the rear shafts for the Ridgeline. It's a similar system. If it is good enough for a performance hatch it should be good enough for this truck.
 

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I drained the 2G rear diff at 2500 miles, to see if the fluid was getting trashed due to new car break-in. This happened to all S2000s, at 2500 miles the S2000 dif oil looked like black paint. After the initial service, the dif could go 35k miles and fluid drained clean. Leaving this trashed fluid in the dif until the Honda recommended interval caused a lot of early dif problems.

Happy to report the G2 dif fluid came out like brand new. Not a single spec of contamination. In a comparison of the used fluid to the new, they were identical in pink tint. This shows the G2 diff is doing extremely well as far as wear. And I drive the truck like a sports car.

Drove my truck in the snow the other day, thought I chipped a tooth in the trans or dif. There was a rythmic rapid thumping coming from the drive line. Snow had piled on top of the driveshaft, and a sticker on the shaft was peeling back, beating the snow like a drum. Driveshaft definitely spinning :)

So be aware of rapid driveline thump in snow and don't worry. I pushed the snow out with a wood stick and the noise disappeared.

There is also a separate front gearbox oil. I'll be draining it at 10k miles, along with a valve adjustment to see how things are doing.
 

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The shaft to the rear wheels turns whenever the vehicle is moving.

The rear drive shaft turns a ring gear in the rear unit, but there is no "differential" in it.

Drive to either rear wheel, or both rear wheels is done through a multi-disc clutch on each side of the ring gear. The stepper motors for each clutch control engagement pressure and therefore the amount of slippage, from some to none, independently on either or both sides, depending on orders from the powertrain computer.

In normal cruising, only the front wheels are driven. Wheelspin, hard acceleration or hard cornering will cause the rear unit to send power to either or both rear wheels as determined by the computer.

The control logic does not wait for wheelspin to drive the rear wheels on hard acceleration.

Well, I am wrong about some of this! The iVTM-4 system in the 2nd gen Ridgeline has hydraulically actuated clutches. A single electric motor driven pump supplies hydraulic pressure through a linear solenoid to either or both clutch packs.

The system is 100% front drive nearly all of the time.

The rear gear ratio is 2.7% taller than the front so the rear wheel(s) are overdriven when either or both left and/or right clutches are engaged.

Since a 235/60-18 tire rolls about 716 revolutions per mile, the 2.7% "slippage" is 19 revolutions per mile difference in speed between the driving and driven clutch discs. At 60 mph, that's only 19 rpm.

Because the clutches are not applied in cruising, this "slippage" should not significantly wear the friction material at all.
 

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The system is 100% front drive nearly all of the time.
Some references I've seen refute that statement. I can't remember who posted this very informative link in another thread, but it states that the SH-AWD in the current TLX/MDX (and the Pilot/Ridgeline's i-VTM4) is always sending at least 10% of the power to the rear wheels. There's even a mention in the Acura MDX page that reinforces this statement:
To improve fuel efficiency, up to 90% of the power is sent to the front wheels when cruising in a straight line.
"Up to" meaning that the power sent to the front wheels is <=90% at any given time. It's not ever 100% front wheel drive, unlike the older VTM4 system.

Because the clutches are not applied in cruising, this "slippage" should not significantly wear the friction material at all.
Regarding clutch wear over time, the first link also contains this little nugget:
Why the SH-AWD does not need to worry about the wear and overheating?

To answer this question, we need to remember: the clutch pack in the SH-AWD is NOT mainly responsible for transmitting power, instead it is used to “modulate” the torque transfer relationship between the Ring Gear (input) and Planet Gear Carrier (output), there is much less stress applied on the clutch plates.
 

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Some references I've seen refute that statement. I can't remember who posted this very informative link in another thread, but it states that the SH-AWD in the current TLX/MDX (and the Pilot/Ridgeline's i-VTM4) is always sending at least 10% of the power to the rear wheels. There's even a mention in the Acura MDX page that reinforces this statement:

"Up to" meaning that the power sent to the front wheels is <=90% at any given time. It's not ever 100% front wheel drive, unlike the older VTM4 system.



Regarding clutch wear over time, the first link also contains this little nugget:
I read the link. Assuming the 2017 Ridgeline iVTM-4 system operates the same as the 2016+ Pilot (a reasonable assumption), there is indeed at least 10% of the torque going to the rear wheels all the time. That is a very informative link, thanks!
 
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