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Old 05-10-2003, 01:19 PM   #26
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I've read all that before and more and still have more questions than answers.
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Old 05-10-2003, 01:48 PM   #27
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Quote:
Originally posted by strangerq
I've read all that before and more and still have more questions than answers.
Same here...guess we'll have to wait and see
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Old 05-10-2003, 02:28 PM   #28
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guys, that writeup is just a laymans explanation of how the centre diff affects the handling, technically it is wrong.

The only way to change a torque split ratio in an AWD system is to change the mechanical gearing of the centre diff, the DCCD doesnt do that. Efectively all the DCCD is doing is varying the amount of permisible slip that can ocur in the centre diff. Fully open means you can get into a situation where all power is going to the rear wheels when you get them spinning up, this is how i can do power slides with full oposite lock aplied, that doesnt mean the torque split isnt a natural 65/35 ratio, just in the same way as an open front diff in a FWD car has a 50/50 split left/right yet when you get stuck in mud all the power goes to one wheel.

When you have the diff fully locked, that means no slip is permited front/rear, in a straight line you dont get any wind up with this, but as soon as you start to corner the varying amounts of wheel travel causes the diffs to bind up, then you get judering as the centre diff breaks away from fully locked because it cant clamp that much force and you also get the tyres patering as they try and break traction to eliminate the diff windup.

Stick one of these cars in a 15MPH small circle and gradually increase the centre diff lock ratio, you will feel the car binding up and the diff ratio increases to a point where its like aplying the brakes.

The diff lock goes from 0-100% locked, that isnt altering the centre diff ratio.

The other thing is that description says there are 6 positions, thats not correct either, there are 6 display points on the dash, but the changeover is analogue and completely variable.
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Old 05-10-2003, 04:56 PM   #29
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Whoo hoo I was right.
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Old 05-11-2003, 09:07 PM   #30
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Quote:
Originally posted by amdmaxx
auto mode is best unless your name ends in Earnhart..
...and then you're driving with a Ouija board anyway
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Old 05-11-2003, 10:04 PM   #31
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Thanks John.

I don't know why people argue with ya as you have been using the dam thing for a while now!

Cheers,
Leo
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Old 05-12-2003, 02:25 AM   #32
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Old 05-12-2003, 09:18 AM   #33
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Quote:
Originally posted by johnfelstead
guys, that writeup is just a laymans explanation of how the centre diff affects the handling, technically it is wrong.
So answer me what is the effective torque split with a full lock?
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Old 05-12-2003, 04:56 PM   #34
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and whats a good "position" on the DCCD button to provoke oversteer?


thx
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Old 05-12-2003, 05:29 PM   #35
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Quote:
Originally posted by RafalW

So answer me what is the effective torque split with a full lock?
With equal traction on all 4 wheels the torque split is 64:36 rear/front when fully locked, the ratio isnt changing, it never will. Once you get changes in traction then you will get changes in where the torque is going (just like any other car, open or LSD diffs). The centre diff is just a Limited Slip Diferential, it's doesnt have magical powers.

Just imagine if this car had an active front or rear diff, you wouldnt be discussing the diff changing it's torque split Left/Right would you? So whats so diferent about the centre diff that makes this so hard to understand?

All you are doing is changing the rate of lock of the centre diff, it's just like taking out a 15NM viscous diff and replacing it with a 25NM viscous diff, you wouldnt expect that to have magically changed the torque split, just the locking load making it a tighter diff.

All the DCCD does is stops you from needing to physically change the diff unit to change it's locking rate, it does this by aplying an electromagnetic force to a mechanical diff unit. It's not black magic.

Having the DCCD set to open will enable you to break traction easier and provoke oversteer more easily, you can equally have the car oversteering with the diff fully locked, but it takes more effort, power and more weight transfer to get the car into a slip angle where you are oversteering.
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Old 05-12-2003, 06:31 PM   #36
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Quote:
Originally posted by johnfelstead
With equal traction on all 4 wheels the torque split is 64:36 rear/front when fully locked, the ratio isnt changing, it never will.
Very nice. So if I get a stick with wheels (like a fully locked diff)and apply different torque to both ends I will get 35% on one wheel and 65% on the other? Sorry but I do not know the kind of magic which would allow for this.
Quote:
Once you get changes in traction then you will get changes in where the torque is going (just like any other car, open or LSD diffs). The centre diff is just a Limited Slip Diferential, it's doesnt have magical powers.
What kind of changes do you expect with a fully locked diff? Am I missing something? Magic?
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Old 05-12-2003, 07:00 PM   #37
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Read up on how gearing alters torque distribution is my best advice if you want to understand this properly.

Or better still, go and drive the thing and learn what it does/doesnt do.
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Old 05-12-2003, 07:09 PM   #38
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Quote:
Originally posted by RafalW

Very nice. So if I get a stick with wheels (like a fully locked diff)and apply different torque to both ends I will get 35% on one wheel and 65% on the other? Sorry but I do not know the kind of magic which would allow for this.

If you have a stick with 2 wheels each end you have a 50/50 split, thats basically what you would have with a WRX gearbox if the centre diff was locked/welded.

The gearbox in the DCCD doesnt match that analogy, as the DCCD gearbox has 2 sticks with a gear in the middle of it to give you the torque split change.
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Old 05-12-2003, 07:15 PM   #39
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Quote:
Originally posted by johnfelstead
Read up on how gearing alters torque distribution is my best advice if you want to understand this properly.

Or better still, go and drive the thing and learn what it does/doesnt do.
One of the difficulties with these discussions is the way in which terminology is used and allows discussants to talk past one another. A question is asked about the effective torque distribution, which varies: altering the distrubution of torque is the whole point of a torsen sensing lsd.......the answer is given about the torque split set in the gearing, which by definition is fixed and does not vary.

It's also funny that you think driving the car will explain how it functions....given that the information in the parent post that you are correcting comes from someone who IS driving the car.
I do admire your attempts to explain though....and look forward to further explanation.
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Old 05-12-2003, 07:19 PM   #40
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Quote:
Originally posted by johnfelstead

The gearbox in the DCCD doesnt match that analogy, as the DCCD gearbox has 2 sticks with a gear in the middle of it to give you the torque split change.
What change? Do you see why your explanation is confusing everyone? You just spent a great amount of time explaining how the toque split NEVER changes.
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Old 05-12-2003, 07:34 PM   #41
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Quote:
Originally posted by strangerq


What change? Do you see why your explanation is confusing everyone? You just spent a great amount of time explaining how the toque split NEVER changes.
That is a FIXED gearing change that gives you the 64:36 torque split. That gearing never changes.

The WRX has a direct 50/50 torque split, put a variable lock LSD in a WRX and you still have 50/50 torque split. The DCCD setup gives you that 64:36 split irespective of how locked the diff happens to be. Weld the thing solid and you have 64:36, take the Electromagnet away and you still have 64:36. The DCCD is just an LSD, it's not a variable gear kit.

As to driving the car, no disrespect but i have been driving DCCD equiped cars for years, i know what i am talking about.

Top tip, look at what car i drive every single day (1999 WRX STi5 TypeRA)
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Old 05-12-2003, 07:38 PM   #42
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Quote:
Originally posted by johnfelstead
If you have a stick with 2 wheels each end you have a 50/50 split, thats basically what you would have with a WRX gearbox if the centre diff was locked/welded.

The gearbox in the DCCD doesnt match that analogy, as the DCCD gearbox has 2 sticks with a gear in the middle of it to give you the torque split change.
I think you are trying to desperately prove something not logical trying to use an argument that you have a car with DCCD (and it's a older version as well).
Try to think about my analogy not as a point to beat.
Tell me how locked diff can vary torque between front and back?
I am sorry but you just refuse to get it.
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Old 05-12-2003, 07:43 PM   #43
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he said the wrx differential is locked not the sti's. The sti has a variable center diff but it only varies slip in the wheels not torque. The 64-36 split come from the gearing of the 2 driveshafts in the diff and it does not vary.
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Old 05-12-2003, 07:45 PM   #44
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Quote:
Originally posted by RafalW


Tell me how locked diff can vary torque between front and back?
I am sorry but you just refuse to get it.
My point is entirely that, it doesnt matter if the diff is open or locked, the torque split stays the same 64:36.

Just think about this, how would you build a system that gave you 10% torque to the front and 90% torque to the rear. Or for simplicity, 10% torque at one end of a shaft and 90% torque at the other. Simple, you cant do it with a solid shaft, you have to have step off gearing to give you that change in torque and two shafts. Thats all the gearbox in the DCCD cars have in adition to a variable diff.
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Old 05-12-2003, 07:57 PM   #45
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Quote:
Originally posted by johnfelstead
My point is entirely that, it doesnt matter if the diff is open or locked, the torque split stays the same 64:36.
And I can not agree with this point.
Quote:
Just think about this, how would you build a system that gave you 10% torque to the front and 90% torque to the rear. Or for simplicity, 10% torque at one end of a shaft and 90% torque at the other. Simple, you cant do it with a solid shaft,

BINGO!
Quote:
you have to have step off gearing to give you that change in torque and two shafts. Thats all the gearbox in the DCCD cars have in adition to a variable diff.
And this torque bias is only valid in "opened" state. Any amount of extra "lock" transfers some of the torque up to full lock when you get 50:50. Where in your opinion there is an error?
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Old 05-12-2003, 08:17 PM   #46
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torque does not change while the tires have traction the limited slip diff only comes into play when some tires have no traction the diff adjust the speed of the tire to regain traction, but when you are driving down the road with the diff at full lock there is still 64% rear and 36% front torque split.
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Old 05-12-2003, 08:56 PM   #47
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Quote:
Originally posted by afpdl
torque does not change while the tires have traction the limited slip diff only comes into play when some tires have no traction the diff adjust the speed of the tire to regain traction, but when you are driving down the road with the diff at full lock there is still 64% rear and 36% front torque split.
`

Again, appreciate the effort at explanation, but it is still unsatisfactory. Beginning with the fact that the initial torque split is 35% 65%, not 36% 64%. Adding the fact, that we can not tell or determine exactly when or exactly to what degree the differential is redistributing torque. Certainly it is incorrect to state that it responds only to "NO TRACTION", a situation that seldom exists. I have never heard of any LSD that literally functioned that way. I also know that the point is often made that torsen differentials do NOT respond to wheel sleep per se, they don't know anything about wheel-slip per se, they respond to differences in torque. That is a sticking point of many explanations of torsen diffs. Now add to that that DCCD-A supposidly responds to throttle position, g-force, etc.
Hence, still more questions than answers.

John: We understand that you have a similar car, but that does not help us understand your explanation. After all you are adamently contradicting even Subaru's own explanation of how DCCD works. If you wish to dispute statements to the effect that DCCD alters the effective torque distribution, then it would seem that you must start by getting Subaru to stop saying that it does.
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Old 05-12-2003, 10:04 PM   #48
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Quote:
Originally posted by afpdl
torque does not change while the tires have traction the limited slip diff only comes into play when some tires have no traction the diff adjust the speed of the tire to regain traction, but when you are driving down the road with the diff at full lock there is still 64% rear and 36% front torque split.
Your post is in contradiction to a practical advice which started this whole thread. If the dial changes an amount of LSD's lock it means it's lock by this amount all the time regardless of traction (this is resulting in weird noises in turns when it's near full lock) and at the same time through this lock it transfers part of this 65% to fronts up to 50:50 at the full lock.
This is what Subaru says and it has some logic behind it. John's logic is lacking and I do not care if he owns DCCD or not.
Let him improve his logic and I might agree with him but only if it makes some sense.
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Old 05-12-2003, 10:20 PM   #49
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here is the subaru manual for the dccd it mentions nothing about adjusting torque distribution. http://www.scoobynet.co.uk/bbs/threa...hreadID=143750

better explanation of everything and how the diff is not torque sensing
http://forums.nasioc.com/forums/show...hreadid=226610

And THE dccd disscusion thread http://forums.nasioc.com/forums/show...highlight=dccd
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Old 05-12-2003, 10:42 PM   #50
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Quote:
Originally posted by afpdl
here is the subaru manual for the dccd it mentions nothing about adjusting torque distribution. http://www.scoobynet.co.uk/bbs/threa...hreadID=143750
Good links, thanx. Will note though it does mention indeed that locking the diff effectively alters torque distribution so it's not consistent with what you are saying...also I think the 36:64 is a slightly different ratio than the USDM:

"DIFF FREE: No front and rear LSD (Front to rear power distribution=36:64)
DIFF LOCK: The front and rear have an almost direct connection. (Front to rear power distribution=front/rear load distribution)"
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