T-Case Question for you all

[iXguido]

Okay guys this question has been nagging me for quite sometime. If the fluid in the VC leaks out complete, ur awd is toast, but you still have RWD, I know that, what I want to know is, does the VC fluid act as a lubing agent as well as a locking agent? Would my VC be toast if ran with little to no fluid? In other words, if it was ran with little to no fluid for a long time and a person could somehow recharge it, would my AWD be restored to full working order?

Thanks
Willy

[spdracrm3]

the fluid in the VC doesnt leak out completely if the seals fail(there is no pressure inside the VC,and its only filled at about 75% anyway) usually the ATF that leaks in is the problem that contaminates the VC fluid so it no longer locks up properly .and even with a failed VC you still have awd in that the sun gears still provide the 63/37% split as long as all four wheels have traction you just lose the lockup capability when one or more wheel starts to slip. the VC is just a locking device the power/torque split is done by the sun gears.normal driving on the street does not affect the VC as all parts are turing at the same speed
as far as the condition of the VC it depends on how long it has been run in a slipping condition which is what causes the plates inside to move (ie towing on two wheels ) which with/without the fluid/or contaminated fluid can overheat the plates and burn them to the point of warping /discoloring at which point they are useless (under normal conditions there is no heat generated as the lock is an affect of the fliud that is used,many people have the misconception that heat is generated causing the lockup to occur if this were the case the lockup would be very unpredictable at different temperatures and that would not satisfy BMW engineers so the fluid lockup has to be consistant at all temps), i have one cut apart right now that the plates are discolored but not warped so it is prolly ok to rebuild if i can just find a source for the silicone fluid . so basicaly you dont know till you cut it apart

[iXguido]

Wow that was mouthful! Thanks for the information. The reason I am asking though, is not because of a toasted VC, it is more out of curiosity as to if there is a way to make these cars part-time awd instead of full time. Every once in a while it is fun to be able to spin just the back wheels, if you know what I'm saying

[spdracrm3]

Unfortunately there is no safe way to make part time awd or rwd,you could remove the front driveshaft but i would not attest to the longevity of the T-case components if your consistantly spinning the rear tires. the VC fluid is slippery silicone but as stated will overheat and burn eventually as its not made to be constantly shearing during slip/lockup events it meant to lock until traction is regained at which point the shear affect stops and all comonents spin at the same speed and the VC stops working.

[iXguido]

I was under the impression that if there was no VC fluid, the front and rear wheels could spin separate of each other. Having understood it that way, I was going to try and rig a system with a high pressure pump that would enable me to pump the VC fluid in and out of the VC on demand, thus making the car 2wd when I wanted to have fun, and awd if I was feeling responsible :)

[spdracrm3]

well you will need to figure out a way to eliminate the sun gear drive system then also because as long as it is in there the power/torque will be split 37/63 ,the VC is just a locking device "if" the two driveshafts spin at different speeds.
as far as rigging a pump to add/remove fluid from the VC you really need to see one apart and see the fluid (it is basically a paste that doesnt like to move,which is why it works to lock up and makes it very difficult to fill the VC ) to understand what you wish to do is impossible ,especially with the VC spinning at 3000rpm

it is very hard to understand the concept of how this system works it took me a while (taking one apart really helps) and i have read all the discussions on various bmw web sites of people trying to describe and figure it out and there is a lot of misinformation unfortunately which makes it even harder . knowing how sun gear systems work and realising the VC is just a lock-up device between the two outputs of the sun gear system will get you a long way to understanding it (the VC cannot and does not change the power/torque distribution which is controlled by the sun gears)

[iXguido]

okay that is starting to make sense. well maybe figuring out how to disconnect the sun gear is my solution instead of trying to pump solids out of the VC, lol. does that sound a little more feasible to you? maybe I just need to take the VC off my auto tranny and take it apart. I'd have to do it anyway I guess. I know there's a way to do what I want, it's just a matter of how, and how much money :P but I'm ambitious

[spdracrm3]

well you could just weld the sun gears together (similar to welding a diff ,but very permanent/destructive) and then remove the front driveshaft when you want 2wd .that would be much easier that completely redesigning the T-case . in awd mode it would act like a completely locked system which of course would affect handling which is why bmw designed with the VC to eliminate that affect.

personally i think your best bet would be to figure out how to adapt a shiftable production TC out of another vehicle to attempt what your doing. or just buy a cheap E30 rwd for drifting

[iXguido]

I understand where you're coming from. But there would be a cool factor involved in this you know, well using the ix t-case that is. I will look into the options of getting a part time t-case from another vehicle, but I really want to, especially for the learning experience, to try this with the ix 'case. I might just buy a rwd e30 for drifting anyway, we'll see.

[spdracrm3]

yup understand what you mean too ,its just why mess with a fantastic design when there are plenty of poor designs out there(not to mention ungodly expensive).

if you want to see sun gear systems taken to the extreme read up on the Toyota Prius transmission the engineer that design that was brilliant as that is a piece of art (amazingly seemless infinite power combinations from two power sources)