No rear wheel drive

A_Kinky_SHO

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Hey guys, recently had my 2010 sho on a 2 post lift, replacing other things, but looking for the source of some vibration.
Car was on and put in gear (no throttle) on the lift to check driveshafts, engine mounts, etc.
We noticed the rear wheels and rear driveshaft didnt spin, and the "Check AWD" message came on the dash.
Its worth noting that my advancetrak is not working (light on the dash).

Is my ptu possibly damaged? Any insight would be greatly appreciated.
 

toms89

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Power to the rear wheels is engaged / disengaged at the rear differential. The PTU always sends power to the rear, the driveshaft to the rear should be spinning, so it sounds like the ptu may be broken. At least that's my understanding on how this haldex system works.
 
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toms89

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Were both front wheels spinning? I guess it's possible that if the front right wheel is not spinning that power is not getting through the differential and/or ptu. Basically then it's sending all the power to the front left wheel. Path of least resistance?!
 
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A_Kinky_SHO

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Both front wheels were spinning.
The front-right wheel was spinning much faster than the left.
 

toms89

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When you say rear driveshaft you do mean rear driveshaft, not axles or half shafts, correct? Because you could have the rear driveshaft spinning but not the rear axles. The RDU controls when power is sent to the rear axles so the driveshaft may be spinning but not the rear axles if the rdu is not demanding it.
 

A_Kinky_SHO

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When you say rear driveshaft you do mean rear driveshaft, not axles or half shafts, correct? Because you could have the rear driveshaft spinning but not the rear axles. The RDU controls when power is sent to the rear axles so the driveshaft may be spinning but not the rear axles if the rdu is not demanding it.
The shaft connecting the ptu to the rear differential is not spinning and can me moved freely by hand, even in gear or park
 

Bluezone

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The shaft connecting the ptu to the rear differential is not spinning and can me moved freely by hand, even in gear or park
If you can spin your drive shaft by hand with it in park, then the PTU is shot. It means that the either the ring gear/pinion gear or one of the other gears in the PTU or both are stripped of teeth.
The PTU is geared directly off the front differential via a PTO shaft. There's no way you should be able to turn the drive shaft by hand with the car in park. It will always rotate with the front wheels if everything is working correctly.
 
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SeanDev

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If you can spin your drive shaft by hand with it in park, then the PTU is shot. It means that the either the ring gear/pinion gear or one of the other gears in the PTU or both are stripped of teeth.
The PTU is geared directly off the front differential via a PTO shaft. There's no way you should be able to turn the drive shaft by hand with the car in park. It will always rotate with the front wheels if everything is working correctly.
Car was designed to always send 10% power to rear at all times. And he is 100% correct, car in park, no way should the driveshaft move. If you change the PTU, clean splines and have them look at carrier bearing on driveshaft. Lucky that PTU didn't explode and just broke. If non PP I recommend modifying and putting in a drain plug, a magnetic one.
 

802SHO

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Speaking from experience I’ve had my car on a lift and at home on jack stands 2 years apart, each time it was put in gear all 4 wheels spin. First time was in 2018 doing my first trans drain and fill on a lift, put the car in gear to cycle through the gears. Second time was in 2020 at home to try to find a noise, and all 4 wheels spin with no throttle and with throttle. As long as that driveshaft is turning your rear wheels will turn, unless your RDU is toast. I also found that while doing my Traction Concepts RDU lsd install, I couldn’t turn the gears at all by hand, I was only able to get them to turn by putting the RDU vertical on the driveshaft end, and rotate the housing by simulating the driveshaft turning. Thus revealing its mechanically operated with an electric aid….but isn’t electrically driven….if that makes sense. The magnet and viscous coupler send “more” power to the rear, but with the driveshaft turning from the front diff to PTU…it’s mechanically going to turn no matter what. Also to add, after a few min of driving off the ground, service advance trac chimed and the car didn’t seem to like this at all…..but once turned off, put back on the ground and then started later, all was back to normal and the car was happy again.
 

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