325iX without front driveshaft - no power to rear wheels

[H-M]

Hello,

My relative has 325iX (as do I) and he removed the front driveshaft because the front diff has some play and he intends to fix it. But the weird (?) thing is that when he removed the front driveshaft from the transfer case no power is transferred to rear either. I (and he as well) thought that the power should still be transferred to rear and the car could be driven as a RWD (at least theoretically). But the car does not move at all. When he reinstalled the front driveshaft the power was sent back to rear and as he says also to front (as he can spin the rear wheels and he feels that the car behaves like 4wd not RWD). Is this normal behaviour or what are we missing here? Would this be normal behaviour if the VC is shot?

Thanks in advance!

[nando]

your VC is shot, that's why.

the VC acts as a limited slip device. it doesn't directly transfer torque to any of the wheels. so when it's bad, the transfercase acts like an open diff. if traction is equal to all 4 wheels, the front & rear get torque split to them via the planetary gear set (approximately 1/3 - 2/3). But if traction is less at one end (effectively 0 without the front driveshaft) no torque will be transmitted to the rear and the car doesn't move. the same thing would happen if you removed the rear driveshaft.

having a functioning VC doesn't determine whether the car is 2WD or not. the ix is always 4wd, because it's the planetary gears that determine the torque split.

if the VC was good, it would lock under acceleration with the front shaft disconnected and the car would move. It would also work the same way if you disconnected the rear shaft, and left the front connected.

[H-M]

Thanks nando. Yes that indeed does make sense. I have to tell him to look for another transfer case then. Some are available, but unfortunately you can never be sure how they have been maintained. Is the VC unit available as a standalone - I guess not? The TC chain would of course be a good thing to exchange as well, but they are not either available as such it seems.. Maybe the whole TC is an only option then..

[nando]

yes you can get a new VC. the cost is around $600 last I looked.

The TC chain isn't NLA but the cost is astronomical. It makes more sense to buy a whole new transfercase!

[325ixa]

But if traction is less at one end (effectively 0 without the front driveshaft) no torque will be transmitted to the rear and the car doesn't move.

i am not sure if i understanded(understood?) this, but i am driving my ix atm without front drive shaft. acceleration is same, top speed same, cornering is not the same, much different than rwd e30. somehow unpredictable.

[flyboyx]

i am not sure if i understanded(understood?) this, but i am driving my ix atm without front drive shaft. acceleration is same, top speed same, cornering is not the same, much different than rwd e30. somehow unpredictable.

no. it really isn't unpredictable at all. the vc in your xfer case is still doing its job. this is the reason your car will move forward under its own power. btw, it is a HORRIBLE idea to drive your car around without its front shaft. you are causing undue stress on your vc and adding to its eventual early demise.

as to the issue of cornering, park your ix next to a rwd car one day with both hoods open. take a look at the difference in the front strut towers. the steering geometry is completely different between the cars. this is one of the main reasons ix's handle differently.

[nando]

i am not sure if i understanded(understood?) this, but i am driving my ix atm without front drive shaft. acceleration is same, top speed same, cornering is not the same, much different than rwd e30. somehow unpredictable.

your VC is good, that's why it works.

it's unpredictable because you don't have your front driveline hooked up.

I don't think you will find agreement that driving with it disconnected is bad or good. The only time it will really stress the VC is under acceleration, but it really shouldn't stress it much - it can only rotate so fast before it will lock, and then it really doesn't matter. at cruising speed, the difference between the front and rear wheels is the same regardless, so I would expect the VC to be doing very little, which is why it seems to work just fine for many people without the front shaft over a long period of time.

[flyboyx]

i am going to have to disagree with you chris. i don't think it makes any difference if the front wheels are spinning at the same rate as the rears if the ds isn't hooked up. i really don't think the tc ever actually locks. it just slips with more difficulty the faster the outputs are spun against each other creating heat. if the front shaft isn't hooked up, the torque will follow the path of least resistance which is the front output. the only thing drawing along the rears is the silicone in the viscous coupling. on acceleration(or at any time the driveline is producing torque), that front will by the laws of physics spin faster than the rear.

[The Dark Side of Will]

cornering is not the same, much different than rwd e30. somehow unpredictable.

If you're really pushing it hard, then you'll notice that the iX has very poor feedback about how close the front tires are to breaking away. A change in pavement conditions may make it transition from cornering to plowing understeer and back to cornering again with almost no steering wheel feedback. This may be why you feel it is unpredictable. This happens because iX's have almost zero caster--about 0.5 degrees.