e30tech.com Forums


Go Back   e30tech.com Forums > Technical > All-Wheel-Drive iX
Register FAQ Members List Sponsors Advertise Shop Search Today's Posts Mark Forums Read







Limited Group Buy: E30 Rear Subframe Camber & Toe Correction Kits - $69 Shipped

Reply
 
Thread Tools Display Modes
Old 12-26-2006, 05:17 PM   #11
chris325ix
Senior Member
 
E30: '91 325ix
Location: bellingham, wa
Join Date: Nov 2005
Posts: 15,574
chris325ix has a reputation beyond reputechris325ix has a reputation beyond reputechris325ix has a reputation beyond reputechris325ix has a reputation beyond reputechris325ix has a reputation beyond reputechris325ix has a reputation beyond reputechris325ix has a reputation beyond reputechris325ix has a reputation beyond reputechris325ix has a reputation beyond reputechris325ix has a reputation beyond reputechris325ix has a reputation beyond repute
Default

I drove 300 miles with a completely stripped front driveshaft (was on a camping trip when it went).

jixer is correct, as long as there is no speed differential between the front and rear wheels, the VC doesn't "see" anything and doesn't do any work. think about it.. if the front and rear wheels are moving at the same speed, the driveshaft splines will be moving at the same speed as well; even if they are completely stripped out and not toucing each other.

now when I took off hard with my car that way, yes the VC would do work (I could tell from the awful noise coming from my front driveshaft). but once you get to cruising speed, it doesn't make any difference wether you have a front driveshaft connected or not.
chris325ix is offline   Reply With Quote
Old 12-26-2006, 05:30 PM   #12
Curtis325is
Senior Member
 
E30: 87-325is 89-325ix(sold)
Location: Canada
Join Date: Jun 2005
Posts: 949
Curtis325is is on a distinguished road
Default

Interesting. I don't see how the transfer case could tell the difference between the front wheels both spinning (so the the front drive shaft has very little resistance) on ice and the front driveshaft removed (no resistance). Maybe because the wheels spinning on ice still provide some resistance and a removed driveshaft provides zero resistance? Logic would tell me that a disconnected front driveshaft would spin very fast because it has no resistance, which would cause the VC to lock. I know that a RWD car with an open diff and one wheel off the ground won't move, the wheel off the ground will get all the power and just spin...but youre telling me the car should still drive with only 1 wheel on the ground.

Still doesn't make sense to me, but I have never tried it. I've see this debate before, and neither side would admit they were incorrect.
__________________
Curtis325is is offline   Reply With Quote
Old 12-26-2006, 06:04 PM   #13
JiXer
Senior Member
 
E30: 1988 325iX Rally, 1989 325iX, 1991 318iS
Location: North San Diego
Join Date: Oct 2006
Posts: 1,176
JiXer has a little shameless behaviour in the past
Default

I think the part you are missing is that a properly functioning VC is looking for a difference (differential) between the front and rear drive shaft speeds. If there is no force or resistance applied to the front output shaft, the VC has no differnces to balance out. The front will do whatever the rear is doing and they spin at the same speed. When you apply force or resistance to the front in a different amount than to the rear, this cause a difference in the speed on one end vs. the other creating shear forces between the discs inside the VC creating the lock up which transfers power away from the faster spinning side.

If you have an open dif situation created by a failed VC, then the result you described (a RWD open dif car with one rear wheel in the air going nowhere) would occur and the car would not move.

Now, I know that makes it sound like the functioning VC is "working" in the first scenario and in fact it is. It is allowing torque to be applied to the rear wheels. BUT, it is not working against itself internally other than slightly during a hard take off or abrupt down shift. However, that is all well within the designed limits of the VC and would not cause premature wear.

So if you see this debated from the other viewpoint, it is safe to assume it is someone who has no experience with this sort of thing and is just trying to sound smart on a message board.

Thats no why I am here. I am here because I love these rare gems and I want to see as many of them stay on the road or in my driveway as possible.

J.
__________________
That's me kickin up all that dirt.

http://www.bigfishmotorsports.com
JiXer is offline   Reply With Quote
Old 12-26-2006, 06:09 PM   #14
Thing-90ix
Contributing Member
 
Thing-90ix's Avatar
 
E30: 325iX
Location: EU
Join Date: Mar 2004
Posts: 1,707
Thing-90ix is an unknown quantity at this point
Default

Ok lets start from the top guys.

1) DO NOT POST BS, if you don't understand how something works then DON'T POST

2) the iX transfer box and how diffs work in general

The e30 325iX is a real 4wd setup. It has a center diff. NOT to be confused with VC, clutch or other methods to drive wheels on cars that are also marketed as "4wd".

The gearing in the center diff sends 37% of torque input to the front drive and 63% to the rear drive, UNDER ALL CONDITIONS, stripped splines or not.

When there is a speed difference between the front and rear drive the VC acts as a brake between the two outputs and heats up as a result (heating power = braking torque provided * rotational speed difference).

Driving a iX without the front or rear driveshaft connected means that the gearing is trying to spin the disconnected output like mad (since the torque resistance there is 0). The only forward propulsion is provided by the VC that will then start braking the spinning shaft and providing more then 0 torque to the other shaft.
DRIVING THE CAR LIKE THIS WILL OVERHEAT THE VC AND MOST LIKELY DESTROY THE REST OF THE TRANSFER CASE ALSO.


"Some people" seem to think that the iX is not a real 4wd setup and hence that only the VC provides the torque to the front wheels. This is not the case. The center diff provides torque to the front and rear, the VC only acts as a diff lock.


The "awful noise" described by chris325ix is caused by the torque transmission capability of the partly destroyed splines jumping over each other. In this case the front output shaft in the transfer box rotates faster then the rear output shaft so the VC will start to brake the speed difference and send more torque to the rear.
While cruising the torque output would be low enough for the splines to still transfer all the required torque (37% of whats put into the transferbox), as noticed by the absence of the "awful noise", to the front and hence the VC will not heat up.


Curtis325is:
Don't let yourself be confused. You have it right.
The transfer box in the iX is a open diff with a VC lock (as is the rear diff).
Lifting one of the outputs off the ground renders it unable to move unless the VC is working (and the VC will heat up incredibly if used like this).
chris325iX and JiXer just don't accept that the iX has a center diff and keep confusing it with other cars that are not real 4wd since they don't understand the difference.
Thing-90ix is offline   Reply With Quote
Old 12-26-2006, 06:55 PM   #15
JiXer
Senior Member
 
E30: 1988 325iX Rally, 1989 325iX, 1991 318iS
Location: North San Diego
Join Date: Oct 2006
Posts: 1,176
JiXer has a little shameless behaviour in the past
Default

OK. First off. Much better. Providing us an idea of how you understand things is a much better approach than Saying we don't understand how things work. You still have a few things wrong.
Quote:
Originally Posted by Thing-90ix
1) DO NOT POST BS, if you don't understand how something works then DON'T POST
First, What I am posting is not BS and it is totally unecesary for you to say things like that and I actually do understand how a differential works, so I will ask you again, to stop insulting me.
Quote:
Originally Posted by Thing-90ix
The gearing in the center diff sends 37% of torque input to the front drive and 63% to the rear drive, UNDER ALL CONDITIONS, stripped splines or not.
True.
Quote:
Originally Posted by Thing-90ix
When there is a speed difference between the front and rear drive the VC acts as a brake between the two outputs and heats up as a result (heating power = braking torque provided * rotational speed difference).
heat has absolutely nothing to do with how the VC works in an iX. The VC works on shear forces provided by a special silicone compound that gets more viscous when it is put in to motion between the plates inside the VC. It is the motion of the fluid that makes its viscosity change, not heat. Which is why the VC will work when it is dead cold just as well as when it heats up.
Quote:
Originally Posted by Thing-90ix
Driving a iX without the front or rear driveshaft connected means that the gearing is trying to spin the disconnected output like mad (since the torque resistance there is 0). The only forward propulsion is provided by the VC that will then start braking the spinning shaft and providing more then 0 torque to the other shaft.
This is only partly true. The condition you describe would only exist under a hard take off and only for a brief second because once everything is spinning together, there are no longer any differential forces going on inside the VC. Everything is now spinning in harmony. No friction, no heat, no problem. Now, if you were to tow the car on two wheels with BOTH DS's in place, you would be forcing one end of the system to be spinning while the other would be standing still. And THAT for certain would cause an intense heating situation inside the VC causing it to literally come apart at the seams and leak out all of the silicone goo in to the ATF. I still believe the is this cause of MANY if not mostly all of the VC failures in iXs.
Quote:
Originally Posted by Thing-90ix
DRIVING THE CAR LIKE THIS WILL OVERHEAT THE VC AND MOST LIKELY DESTROY THE REST OF THE TRANSFER CASE ALSO.
Simply not true. It will not harm a thing as has been proven many times over. You have no background of any testimonials for anyone that can honestly state that they had a working VC prior to removing the front DS and a failed one after re-installing b/c it simply doesn't happen.
Quote:
Originally Posted by Thing-90ix
JiXer just don't accept that the iX has a center diff and keep confusing it with other cars that are not real 4wd since they don't understand the difference.
Again, you are making an ass out of yourself by trying to tell other people what I understand and what I don't.
I am now going to end my involvement in this debate as I have stated the facts as clearly as I can. If anyone has any other specific questions, feel free to contact me:
j@dirtye30.com

J.
__________________
That's me kickin up all that dirt.

http://www.bigfishmotorsports.com
JiXer is offline   Reply With Quote
Old 12-26-2006, 07:45 PM   #16
Thing-90ix
Contributing Member
 
Thing-90ix's Avatar
 
E30: 325iX
Location: EU
Join Date: Mar 2004
Posts: 1,707
Thing-90ix is an unknown quantity at this point
Default

Quote:
Originally Posted by JiXer
Quote:
Originally Posted by Thing-90ix
1) DO NOT POST BS, if you don't understand how something works then DON'T POST
First, What I am posting is not BS and it is totally unecesary for you to say things like that and I actually do understand how a differential works, so I will ask you again, to stop insulting me.
To me posting something that isn't correct is BS. I'm sorry if you feel otherwise.
I do exaggerate my text somewhat, mostly because strong feelings are not relaid through a forum in other ways.


Quote:
Originally Posted by JiXer
Quote:
Originally Posted by Thing-90ix
When there is a speed difference between the front and rear drive the VC acts as a brake between the two outputs and heats up as a result (heating power = braking torque provided * rotational speed difference).
heat has absolutely nothing to do with how the VC works in an iX. The VC works on shear forces provided by a special silicone compound that gets more viscous when it is put in to motion between the plates inside the VC. It is the motion of the fluid that makes its viscosity change, not heat. Which is why the VC will work when it is dead cold just as well as when it heats up.
Notice the "as a result". The braking provided by the VC produces heat, heating up the VC.
The VC does provide braking at 0 speed difference, but this is quite small compared to the max braking force that it can provide.

Quote:
Originally Posted by JiXer
Quote:
Originally Posted by Thing-90ix
Driving a iX without the front or rear driveshaft connected means that the gearing is trying to spin the disconnected output like mad (since the torque resistance there is 0). The only forward propulsion is provided by the VC that will then start braking the spinning shaft and providing more then 0 torque to the other shaft.
This is only partly true. The condition you describe would only exist under a hard take off and only for a brief second because once everything is spinning together, there are no longer any differential forces going on inside the VC. Everything is now spinning in harmony. No friction, no heat, no problem. Now, if you were to tow the car on two wheels with BOTH DS's in place, you would be forcing one end of the system to be spinning while the other would be standing still. And THAT for certain would cause an intense heating situation inside the VC causing it to literally come apart at the seams and leak out all of the silicone goo in to the ATF. I still believe the is this cause of MANY if not mostly all of the VC failures in iXs.
Quote:
Originally Posted by Thing-90ix
DRIVING THE CAR LIKE THIS WILL OVERHEAT THE VC AND MOST LIKELY DESTROY THE REST OF THE TRANSFER CASE ALSO.
Simply not true. It will not harm a thing as has been proven many times over. You have no background of any testimonials for anyone that can honestly state that they had a working VC prior to removing the front DS and a failed one after re-installing b/c it simply doesn't happen.
The "everything spinning together" effect is caused by the braking action of the VC, producing heat while doing so. If a driveshaft is removed then the open end doesn't know crap about what speed the wheels are spinning at so it doesn't matter how fast you are going.
The effect of running without a driveshaft is exactly the same as forcing the front and rear wheels to turn at different speeds. The speed difference will simply be a function of how much torque is applied to the transferbox. The VC doesn't know or care *why* there is a speed difference.

Continuously heating the VC = dead VC. Very simple.

The only possible way for your claims to have any merit at all would be for the VC braking force at 0 speed difference to be high enough to drive the car as such. And no, it isn't.
Try it for yourself, pull out a front halfshaft from the front diff and park the car in gear on a slight slope. The VC even then allows the car to slowly roll down hill. The force needed to maintain cruising speed is MUCH higher then that.

The whole basis for the weird views you have seem to be people running cars with partly stripped splines on the front driveshaft. The answer to that is as I posted previously. Running with no driveshaft connected WILL NOT WORK (for very long, say more then 5min), and I have yet to see a single claim of anything like that.
Thing-90ix is offline   Reply With Quote
Old 12-27-2006, 12:15 AM   #17
chris325ix
Senior Member
 
E30: '91 325ix
Location: bellingham, wa
Join Date: Nov 2005
Posts: 15,574
chris325ix has a reputation beyond reputechris325ix has a reputation beyond reputechris325ix has a reputation beyond reputechris325ix has a reputation beyond reputechris325ix has a reputation beyond reputechris325ix has a reputation beyond reputechris325ix has a reputation beyond reputechris325ix has a reputation beyond reputechris325ix has a reputation beyond reputechris325ix has a reputation beyond reputechris325ix has a reputation beyond repute
Default

Quote:
Originally Posted by Thing-90ix
The "awful noise" described by chris325ix is caused by the torque transmission capability of the partly destroyed splines jumping over each other. In this case the front output shaft in the transfer box rotates faster then the rear output shaft so the VC will start to brake the speed difference and send more torque to the rear.
While cruising the torque output would be low enough for the splines to still transfer all the required torque (37% of whats put into the transferbox), as noticed by the absence of the "awful noise", to the front and hence the VC will not heat up.
my front driveshaft was bad enough that it wasn't capable of transfering any torque at all. when I pulled it out the splines were smooth.. but it did have enough there to make a pretty ugly noise if I held the brakes down and stepped on the gas (it's not exactly a smooth bearing surface).

although maybe you're right, maybe the splines had enough in them that the could hold enough torque to keep the VC from slipping once I got up to a constant speed. but the amount of torque we are talking about is trivial, considering by the time I had done a few starts and stops, I could hear the splines slipping when stopped at lights with the engine only at idle. I seriously doubt it's enough to damage the VC (I drove over 300 miles that way at freeway speeds). I had that same VC in my car for 4 years after that and it always worked perfectly.

Quote:
Originally Posted by Thing-90ix
Curtis325is:
Don't let yourself be confused. You have it right.
The transfer box in the iX is a open diff with a VC lock (as is the rear diff).
Lifting one of the outputs off the ground renders it unable to move unless the VC is working (and the VC will heat up incredibly if used like this).
chris325iX and JiXer just don't accept that the iX has a center diff and keep confusing it with other cars that are not real 4wd since they don't understand the difference.
I'm not sure what you are trying to prove here. I know very well the differences between other "awd" setups (including the VC style used by early VWs, and the clutch style used by some japanese cars). I've never said anything in any of my posts about other AWD systems. I'm not trying to prove anything here.

once again you start with personal attacks and insulting my intelligence. maybe I would take your points more seriously if you could communicate without resorting to grade school insults.
chris325ix is offline   Reply With Quote
Old 12-27-2006, 12:36 AM   #18
JiXer
Senior Member
 
E30: 1988 325iX Rally, 1989 325iX, 1991 318iS
Location: North San Diego
Join Date: Oct 2006
Posts: 1,176
JiXer has a little shameless behaviour in the past
Default

Quote:
Originally Posted by chris325ix
although maybe you're right, maybe the splines had enough in them that the could hold enough torque to keep the VC from slipping once I got up to a constant speed. but the amount of torque we are talking about is trivial, considering by the time I had done a few starts and stops, I could hear the splines slipping when stopped at lights with the engine only at idle.
Torque is of no signifigance here. The VC does not differentiate between torque. There is a planetary gear in the TC that splits up the torque. The VC's function is to manage the differentiation of ROTATIONAL SPEEDS between the two output shafts.

J.
__________________
That's me kickin up all that dirt.

http://www.bigfishmotorsports.com
JiXer is offline   Reply With Quote
Old 12-27-2006, 05:05 PM   #19
robbieosterman
Member
 
E30: None
Location: Florida
Join Date: Nov 2006
Posts: 33
robbieosterman can only hope to improve
Default

So, as it seems from what I've read and from my experience of the failure...

Is that once the Viscous Coupler fails either from a disconnected front driveshaft (or stripped out) the viscous coupler fails to heat up and maintain a thick viscousity making the transfer case an open differential.

A working V.C would be found if you had either the front of rear wheels lifted off the ground. If the car moves forward without much loss of torque, then your V.C is okay.

However, a failing V.C would show symptoms of less and less torque being split to the wheels with traction...

And a completely failed V.C would have power sent to the wheels with least resistance (in many examples, a stripped front driveshaft) then you would lose all forward motion.

I believe the cause of failure of the viscous coupler on my car was driving on a flat tire for a while, and with the rolling diameters different, the V.C was trying to send power around, and with 146,000 miles on the unit, it just couldn't handle the stress and failed. I still don't understand WHY the front shaft stripped out but it was what caused the complete loss of power.

Once I remove the case from the car, I'll make sure to pull it apart and take some high resolution pictures for the community to see.

Lesson to be learned - if you have a high mileage car, make sure your splines are in check, and if you can, check the condition of your viscious coupler. If ya don't, you might end up on the side of the road waiting for a tow like me!
robbieosterman is offline   Reply With Quote
Guest Message
Tire Rack - Pure Control
Old 12-27-2006, 05:30 PM   #20
JiXer
Senior Member
 
E30: 1988 325iX Rally, 1989 325iX, 1991 318iS
Location: North San Diego
Join Date: Oct 2006
Posts: 1,176
JiXer has a little shameless behaviour in the past
Default

Hey Robbie!
You should give it another read. You got a few things, but missed a few others.
Quote:
Originally Posted by robbieosterman
Is that once the Viscous Coupler fails either from a disconnected front driveshaft (or stripped out)
This will not cause the VC to fail
Quote:
Originally Posted by robbieosterman
the viscous coupler fails to heat up and maintain a thick viscousity making the transfer case an open differential.
The VC does not rely on heat in any way shape or form. The goo inside the VC thickens from the shear forces created in between the thin disks encased in the VC. If anything, it would work better when cold as the goo would be more viscous at lower temps.

Once a VC fails, the TC does become an open center diff.
Quote:
Originally Posted by robbieosterman
A working V.C would be found if you had either the front of rear wheels lifted off the ground. If the car moves forward without much loss of torque, then your V.C is okay.

However, a failing V.C would show symptoms of less and less torque being split to the wheels with traction...
Couldn't really follow you there. If you do a "jack test" (if you don't know how to do this safely, search the forum) with the rear wheels off the ground, a functioning VC will begiin to pull the car forward as soon as the clutch plate begins to engage. A VC can fail gradually meaning that you may have to half the clutch half or fully engaged to see the car begin to move. If the clutch is let all the way out and the car still isn't moving, the VC is completely shot. I believe that once the failure is onset, it comes on very quickly. At least that was the case with mine. The goo can break down over time, but the VC will usually not fail until there is sufficient heat
built up to burst the case and leak the fluid out. Also, the disks inside the VC have tiny barbs on them that help to drag the fluid along. From what I understand, these can wear down over time (I assume form making contact with the adjacent disks) which can also lead to a degraded performance from the VC.
Quote:
Originally Posted by robbieosterman
And a completely failed V.C would have power sent to the wheels with least resistance (in many examples, a stripped front driveshaft) then you would lose all forward motion.
Yes. A car with the front drive shaft removed and a toasted VC will not move.
Quote:
Originally Posted by robbieosterman
I believe the cause of failure of the viscous coupler on my car was driving on a flat tire for a while, and with the rolling diameters different, the V.C was trying to send power around, and with 146,000 miles on the unit, it just couldn't handle the stress and failed. I still don't understand WHY the front shaft stripped out but it was what caused the complete loss of power.
It may have helped push it over the edge, but age and lots of loose traction driving are far more likely culprits depending on how far you drove. Despite popular belief, these VC's are pretty tough. You could even tow an iX on a dolly a few miles at low speed without causing any damage, but I would NEVER reccomend doing so.

Quote:
Originally Posted by robbieosterman
Once I remove the case from the car, I'll make sure to pull it apart and take some high resolution pictures for the community to see.
Hope this helped.

J.
__________________
That's me kickin up all that dirt.

http://www.bigfishmotorsports.com
JiXer is offline   Reply With Quote
Reply


Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump


All times are GMT -4. The time now is 11:09 PM.






Powered by vBulletin® Version 3.6.8
Copyright ©2000 - 2017, Jelsoft Enterprises Ltd.