Worn out T-case chain

[nando]

agreed

I don't think it will work if the seal pops and fluid comes out, it might retain some torque but the car wouldn't move very quickly and it would probably cause a cycle of more heat/more leakage.

[The Dark Side of Will]

no, it probably won't destroy it. it just puts a load on it. the biggest load would be during acceleration, at a cruise it would be small.

I know several people who've done it before for years without issue.

Like I mentioned to SPDACRM3, I would never have thought that the VC could take that kind of waste heat output for long. Educated.

It probably depends on how hard it's driven, as the amount of waste heat it develops is proportional to the product of RPM drop and transmitted torque, both of which depend on applied torque.
Apply more torque, develop more waste heat... get the temp up high enough that the internal pressure pops a seal and it's done.

However, even with a seal popped it's going to retain a small amount of fluid... I don't know if that would be enough to have significant torque transmission or not.

[duffyboby]

no, it probably won't destroy it. it just puts a load on it. the biggest load would be during acceleration, at a cruise it would be small.

I know several people who've done it before for years without issue.

So that settles it, thanks.

[nando]

no, it probably won't destroy it. it just puts a load on it. the biggest load would be during acceleration, at a cruise it would be small.

I know several people who've done it before for years without issue.

[duffyboby]

so running the car without a front driveshaft will destroy the VC and eventually the car will not move any more, I got awfully confused about this with the argumentation going on, I thought you could run an iX without front driveshaft, with a good VC, without any problems, except for the danger of the splines rusting out, obviously. Ive seen many go without problems.

[nando]

with the front driveshaft disconnected, yes.

[duffyboby]

I might be completely off, but wouldn't a burnt VC act as an open diff, thus sending all the power to the front and resulting to the car not moving?

[The Dark Side of Will]

No, I'm not going to go destroy my VC to demonstrate anything.

So every example that you've "followed" passed the jack test afterward? Links/Citations?
How many of those later had the T-case torn down to investigate the VC?

*IF* the VC survived, then that would show that it can take a pretty hefty continuous heat load. Impressive. I'd have to do some calcs on exactly how much, but it's a lot.

Even if that's the case, your understanding of the T-case is still flawed. :p

[spdracrm3]

Irrelevant. (Difficult to diagnose; most people aren't abusive enough to just pull the driveshaft and go on their merry way).

Tell me why I'm wrong.

so you have no proof ?

as stated ,every single IX i have followed a write-up on that pulled the front shaft due to stripped/noisy front splines and driven thousands of miles until it could be repaired had had Zero issue with AWD functionality once repaired (one was driven 3 years as a 2wd). so explain away or prove otherwise.....

[The Dark Side of Will]

Irrelevant. (Difficult to diagnose; most people aren't abusive enough to just pull the driveshaft and go on their merry way).

Tell me why I'm wrong.

[spdracrm3]

just show me ONE IX that killed its VC by removing the front driveshaft.......

[The Dark Side of Will]

just tired of the mis-information being spread about how this T-case works

Then stop spreading it ;-)

wrong the output shafts will be turning at different speeds on ice if one set of wheels is slipping ,without a front shaft the outputs will spin at the same speed (other wise the jack T-case test wouldnt work)

Here's the data point that demonstrates why it doesn't work the way you think it does:

Viscous coupling torque:
0 RPM: 0 fltbs
150 RPM: 50 fltbs.

That's it.

A conventional clutch pack LSD has a spring and frictional preload such that at 0 RPM it has 65 ftlbs of preload. You seem to think that a viscous coupling works like that. It doesn't. A viscous coupling does not have any preload torque.

So here's how things actually work in the T-case (using some convenient numbers for example only):

150 ftlbs at 1000 RPM at the T-case input
Planetary gearset wants to send 50 to the front and 100 to the rear.

With the driveshaft and 3.91 diff gears, this turns into 195 ftlbs at the front axle and 391 ftlbs at the rear axle and the car moves forward.

WithOUT the driveshaft, the front output will start to speed up. At 0 RPM, the VC exerts 0 torque, so the VC can NOT keep the front output from turning while the rear is stationary.

As the front output accelerates, the VC will develop increasing torque until it hits your data point of 50 ftlbs at 150 RPM. At that point, the VC is redirecting all 50 ftlbs of the front driveshaft's torque to the rear driveshaft and the car moves. The front output is turning 1075 RPM and the rear is turning 925 RPM with all 150 ftlbs showing up at the T-case input.

Obviously, the viscous coupling is dropping 150 RPM and 50 ftlbs... So we calculate 50 * 150/5252 = 1.43 horsepower. That's 1.43 horsepower or 1,065 Watts of waste heat developing in the viscous coupling. It dies quickly.

[spdracrm3]

" I don't feel like wearing out my keyboard educating you."

likewise!

just tired of the mis-information being spread about how this T-case works

"The viscous coupling transfers torque based on the speed difference. Not having a front driveshaft is just like having the front tires on ice."

wrong the output shafts will be turning at different speeds on ice if one set of wheels is slipping ,without a front shaft the outputs will spin at the same speed (other wise the jack T-case test wouldnt work)

[The Dark Side of Will]

nope not at all

what kills VC is output shafts spinning at different speed (ie 2 wheel towing) if you remove the front drive shaft the VC will have the two outputs locked together (front output socket has no load so will freely spin at the exact same speed as the rear output due to locking provided by VC) ...therefore no difference in speed between the two shafts = no damage to VC .

Go research how the center diff inside the VC works, then come back and tell us all about it.

This has been covered dozens of times before and I don't feel like wearing out my keyboard educating you.

EDIT: I guess I can be a nicer guy than that...

WITHOUT the VC, but with the driveshaft, the car moves by routing 2/3 of transmission output torque to the rear and 1/3 to the front. This is accomplished by a planetary gearset. Both driveshafts turn the same RPM.
If the front tires are on ice, then all the torque goes to the front driveshaft and the rear gets none. This is how an open diff works.

WITH the VC, as the front tires slip on the ice and accelerate, an RPM difference develops between the front and rear driveshafts. This RPM differences causes the viscous coupling to exert a torque on the slower shaft. It's been posted* (by YOU!) that this torque is 50 ftlbs at 150 RPM. I think it's proportional to the square of RPM, so the torque transfer goes up very quickly with speed difference.

The viscous coupling transfers torque based on the speed difference. Not having a front driveshaft is just like having the front tires on ice. The speed difference between the front and rear outputs is what causes the VC to send torque to the rear.

With a good VC, the car will drive without the front (or rear for that matter) driveshaft, BUT that will be at the expense of continuous slip across the VC with the VC transmitting ALL of the drive torque. This grossly overloads the VC, causes it to develop a lot of heat and can blow the seals out and spill the silicone all over the inside of the T-case, killing the VC.

* http://www.r3vlimited.com/board/showthread.php?t=337266

[spdracrm3]

Umm... please tell me this is sarcasm.

nope not at all

what kills VC is output shafts spinning at different speed (ie 2 wheel towing) if you remove the front drive shaft the VC will have the two outputs locked together (front output socket has no load so will freely spin at the exact same speed as the rear output due to locking provided by VC) ...therefore no difference in speed between the two shafts = no damage to VC .