Quick question, some say that you can just forget about it and leave it 2wd but if the splines between the transmission and the TC are chewed up, wouldn't that make it 1wd since it won't power up the passenger side wheel either? Unless i am not seeing it the right way?
If the spines shear it'll operate as a front 2WD. This was confirmed by a forum member who test drove two (yes two) used CX9 AWD right off the dealer's lot that were really FWD with broken transfer cases. Both vehicles drove fine except when in snow the front wheels spun and no movement from rear wheels.
Also, another forum member actually bought a used AWD CX-9 and didn't even know the transfer case was broken until the first snowfall and the front wheels spun with no rear wheel movement.
Check out the video link below, it's a great explanation how
crossover AWD works,
crossover AWD are not like true 4WD systems. Like forum member Drogos said it's like an engineer's band-aid to make a AWD out of a base FWD, check the video out: the front differential is exactly the same for both FWD and AWD
except the AWD has a little spline extension add-on that connects to the PTU that drives the rear shaft. If that spline extension shears off, the rear wheels don't get power anymore and the car basically becomes a regular FWD.
It's really a lazy and cheap easy way for car manufacturers to make an AWD out of what is essentially a FWD car. They're just tapping power from the transmission via the PTU (Power Takeoff Unit) and directing it to the rear where the "real controls and brains" are (there's a rear clutch pack unit that is controlled by the car's computer when slippage is detected) but those "brains" are useless if either the transfer case gears or transmission splines are sheared and there's no power coming from the front.
Crossovers aren't meant for off-roading like true 4WD jeeps, they're really just grocery-getters meant for snow when fitted with good quality all season tires or winter tires.
The real problem is that on the CX9,
BOTH the PTU and rear propeller shaft is TURNING ALL THE TIME when driving the car even when there is no snow. The oil is breaking down from all that unnecessary wear and tear. The oil eventually turns to sludge around the 30k to 40k mark, it'll still run on the sludge but you can bet transfer case oil leaking around 60k mark and then full blown seizure+failure most definitely and guaranteed around 90k mark.
This is not just speculation, it's been proven time and time again from pictures posted by members who did the oil swap, the oil coming out @30K is a blackish gray thick sludge. New OEM transfer case color is a translucent yellow amber color similar to the rear differential oil.
And to add more insult, there's only half a quart of oil in the transfer case. And get this, some dealers of used AWD CX9's may not even know it's broken and it's really a FWD until it snows and their customers complain of spinning front wheels.
Based on info from this forum once the transfer case is decoupled the car drives like a FWD. The decoupling location is random, if gears sheared inside transfer case then just need to replace transfer case $650 + labor, if decoupling point at transmission spines, looking at $3000 transmission + $650 transfer case + labor.
In Russia, the problem is so well known they offer services to fix the transmission spines for $250 instead of replacing the whole $3000 transmission.
Just change the transfer case oil to prevent seizing and you have no worries. It's really not a big deal, it's like changing the engine oil.