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Discussion Starter #1
I know there are DCCD threads out the yang, but none to specifically answer my question and here it is... Would moving the diff lock up more front biased (say one green triangle from teh rear, rather then full rear) - i realize that from the 90 threads they say that the torque split doesnt change, but would this help reduce strain on the rear shaft/axel? For instance would full rear(65/35) be worse then (60/40) on the rear drive train parts? I know this isnt a torque split thing, Im thinking more in terms ofstrain and wear and what not. I just always launch in one triangle from the full open and it seems to do much better then in full rear... so im just curious **puts on flame suit**.

Robert~
 

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I think, just think, that since in complete open the front and rear driveshafts can spin completely independently of each other, most of the torque going to the front wheels causes them to just spin on launch. If you dial in some lock, and force the axles to a closer rate of speed, the rear wheels will end up getting more torque that the front was just wasting. This would mean more power to the rear wheels, and a faster launch.
I know the torque going to the front wheels is wasted some what on launch because of my experiences doing burnouts in my friend's driveway. In DCCD full open, my front wheels spin enough to cause smoke, while my rear wheels seem to spin little or none at all. As I adjusted the DCCD more towards lock, I get noticeable wheelspin at the rear tires. I believe this answers your question as to why your car seems to launch better with some lock. As for the other question, I don't know. If anything, if my above description is anything close to correct, more lock would mean more power to the rear wheels, causing more stress. :-?
 

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Discussion Starter #3
hmm crap... usually people launch on full rear... and if they had axel problems i guess that means you cant go much further back :( hmmm.. thanks for the info. Anyone else?

Robert~
 

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Snowboarders?

IMO - the more power going to the rear the more likely you are to snap a rear axle. I honestly don't understand why people are snapping rear axles with this car and not with your average RWD sports car - the axles must be significantly weaker, because the axle strain with AWD should be less on the rear axle...... because acceleration is balanced out between both.
 

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set to the rear and launch away!!!! ;-)
 

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Mac OS X/Unix/Linux Folks, 4MLA1FN is takin car of you.

Stepping on the gas would make your car's weigh shift to the rear, because of inertia. As most of the weight is "transferred" to the back axle, your rear wheels have to have more traction if you want to do a good launch.

That's why I guess shifting the DCCD to full rear lock would produce a faster launch.
 

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i know of some people that have their quickest 60' while set in auto...??? i will never get this whole dccd thing... :-?
 

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maxwolfinger said:
I think, just think, that since in complete open the front and rear driveshafts can spin completely independently of each other, most of the torque going to the front wheels causes them to just spin on launch. If you dial in some lock, and force the axles to a closer rate of speed, the rear wheels will end up getting more torque that the front was just wasting. This would mean more power to the rear wheels, and a faster launch.
I know the torque going to the front wheels is wasted some what on launch because of my experiences doing burnouts in my friend's driveway. In DCCD full open, my front wheels spin enough to cause smoke, while my rear wheels seem to spin little or none at all. As I adjusted the DCCD more towards lock, I get noticeable wheelspin at the rear tires. I believe this answers your question as to why your car seems to launch better with some lock. As for the other question, I don't know. If anything, if my above description is anything close to correct, more lock would mean more power to the rear wheels, causing more stress. :-?
this doesnt make sense to me, lock is towards the front. full lock is 50/50, the light at the top. why would your front wheels spin on a launch when the rears have 65% and fronts only 35%?
 

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Torque split on the STi is always 65% rear and 35% front.

You're only varying the amount of differential lock ratio front : rear.

I could be wrong, but this is what I understand. Just trying to rationalize what maxwolfinger explained, which makes sense to me.

The reason why your rear wheels won't slip as the fronts do when having the dccd towards the back is because you rear diff is more "locked" than the front is.

When setting the dccd towards the front (lock), then both differentials front and back have the same degree of "lock". But torque split is still 65 rear / 35 front. Your rear wheels could still slip more than the fronts do when hard launching with the center diff in lock, because the rear wheels are still receiving 65% of the engine power.

Please correct me if I am wrong, I still believe I am ignorant about the DCCD thing.

:wink:
 

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Discussion Starter #12
hmmm sounds very informative. Thanks everyone, if anyone else comes apon anything let me know! thanks!

Robert~
 

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What the 50/50 means is IDEALLY, with no slip at either end of the car, half the torque would go to each end of the car. But, as our car is not a true variable torque split but basically an adjustable limited slip unit as I understand it, the 50/50 means the front and rear driveshaft speeds would be identical. If your car had absolutely no traction at the front wheels, only a small amount of torque would be needed to accelerate the wheels, while most of the torque would be going to the rears, assuming they have traction. I still am not 100% on the DCCD thing, but thats my 2 cents.
 

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STi_Thunder said:
Torque split on the STi is always 65% rear and 35% front.
No. It's 65/35 in "open" mode. As soon as you lock the CD, you transfer more to the front. In full lock, it's approximately 50/50 as long as neither the front nor rear wheels are spinning.

You're only varying the amount of differential lock ratio front : rear.
Think of the CD as a drive shaft going to the front and rear, but split at the CD. In open mode, the torque from the engine is split via a planetary gearset so that 65% goes to the rear and 35% to the front. Now imagine that there's an electromagnetic clutch between the two shafts. The more juice is supplied to the clutch, the more "joined" the two ends of the shaft are. While the shafts are joined and the clutch isn't slipping, the torque split is 50/50.

The reason why your rear wheels won't slip as the fronts do when having the dccd towards the back is because you rear diff is more "locked" than the front is.
No, you're confusing the front and rear diffs with the center diff.

When setting the dccd towards the front (lock), then both differentials front and back have the same degree of "lock". But torque split is still 65 rear / 35 front. Your rear wheels could still slip more than the fronts do when hard launching with the center diff in lock, because the rear wheels are still receiving 65% of the engine power.
No, same problem. The lock that the DCCD creates is between the front and rear.
 

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bitabur said:
Hence, more torque at the rear axle, and more potential to snap the rear axle.....
if you do not get the tires to spin, at least 1 rev, then there is more stress on the drivetrain. when the tires spin the strain on axles is reduced.

ted
 

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No. It's 65/35 in "open" mode. As soon as you lock the CD, you transfer more to the front. In full lock, it's approximately 50/50 as long as neither the front nor rear wheels are spinning.
Interesting ... I stand corrected ... :)

When you say "you transfer more", you obviously mean torque. So is the center diff indeed splitting up more torque towards the front the more you move the DCCD towards the LOCK position?
 

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Discussion Starter #17
wow im getting more and more confused as when i try to read the actual DCCD threads.

Robert~
 

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STi_Thunder said:
When you say "you transfer more", you obviously mean torque. So is the center diff indeed splitting up more torque towards the front the more you move the DCCD towards the LOCK position?
Yes, up to ~50/50 at full lock.
 

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Discussion Starter #19
so anotherwords one triangle up from full rear will cause less stress then full rear?

Robert~
 

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staticx313 said:
wow im getting more and more confused as when i try to read the actual DCCD threads.
It's really pretty simple...once you can get your head wrapped around it. My advice is to skip the threads...there are too many people talking about the DCCD who don't understand how it works. Instead, head right to part 1 of the DCC FAQ:

http://wallace.as.arizona.edu/~cgroppi/DCCD_FAQ/DCCD_FAQ.html

(Parts 2 & 3 haven't been written yet.)

I'll warn you: it's not an easy read. I suggest you read it once and try to follow it. If you get stuck, think about it a minute...back up a couple paragraphs, and try again. You'll pick up a lot on the first reading, but probably not everything. Try going through it again every couple weeks until it clicks.

I think I might try my hand at a "DCCD for dummies"-type doc...
 
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