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Old 11-29-2006, 05:39 PM   #26
kingsubi
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Quote:
Originally Posted by Unabomber View Post
Differential FAQ
So what should I upgrade my car with?

RS/WRX center: JDM STi 20kg center viscous unit. This increases the break away torque from the stock 4kg unit to hold rear traction longer.
Just to add here that the 20Kg/mm center is not a very street friendly at all and that STi offers a 12 Kg/mm center diff (rallispec can get them) that provides a great alternative to dccd for beefing up the AWD system.
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Old 11-29-2006, 08:35 PM   #27
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What advantages would one see going from a vicous unit in the rear (WRX) to a Torsen type?

Is there a readily available rear Torsen/helical unit for the WRX?

TIA
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Old 11-29-2006, 09:05 PM   #28
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Yes there is. www.gearboxtech.com sells a Torsen type PPG rear differential. Someone else may make one as well, but that's all I know off the top of my head. As to the advantages...that's a toughy as you have some issues:

viscous vs torsen theory
viscous vs torsen practical application

The theory is that the torsen will be a more stable upgrade in terms of reliability and torque transfer.
The practical application is that the torsen will give you more rear grip.

Both of these are relative offerings based on what I've heard though as like suspension components, you have a quality/known part that is designed to do XXX and there's always a bunch of jackasses that post that it does YYY.
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Old 11-29-2006, 09:18 PM   #29
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^ thanks. I need to start w/ the front- that much I do know
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Old 01-31-2007, 04:36 AM   #30
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Default 2 Way Center Diff

What will a 2 way center diff do in an all wheel drive? Specially with a 1.5 front and rear (not main concern but answer if you like or know, the more knowledge i get the better) Thanks.
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Old 02-01-2007, 03:56 PM   #31
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Great post! Thanks.
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Old 03-02-2007, 11:51 AM   #32
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What lock % is the stock WRX Rear diff capable of?
Where can I find the STi 20Kg center diff?
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Old 03-02-2007, 11:54 AM   #33
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Sti 20kg center can be found at www.rallispec.com
I believe its 978
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Old 03-02-2007, 12:10 PM   #34
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what about the 12kg one? is that special order?
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Old 03-02-2007, 05:21 PM   #35
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12kg is damn hard to find and wont bolt up to our new RS/WRX trannies, hence it's not mentioned.
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Old 03-13-2007, 05:26 PM   #36
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Quote:
Originally Posted by bWRX View Post
I am not finding this FAQ to clear up a lot of my confusion regarding the various diffs that have been supplied stock in the USDM STi.

The 2007 apparently have a Torsen in the rear, as a new thing. I've noted a few posts talking about this like its a really significantly great improvement for some reason. But according to your FAQ, 2007 is the third model year for the USDM STi to have torsens in both front and rear - the 2004s had a suretrac unit in front.

As near as I can tell, it went like this:

2004 - Suretrac front, "mechanical" rear
2005 - "Helical" front, "mechanical" rear
2006 - "Helical" front, "mechanical" rear
2007 - "Helical" front, "Torsen" rear

Now, if really, for all intents and purposes, Torsen = helical = mechanical, I'd like to hear you explain why that is, but me and a lot of guys like me are still standing around out here wondering what the tiny little differences between these various units are, or where we can go to research it ourselves. There is a lot less general info about diffs out there than there is, say, suspension or forced induction concepts.

Thanks!
Here are the part numbers for each of the diffs (front, rear, and center)

Rear Diff

38410AA080 - 2004 Rear Diff Unit
38410AA080 - 2005 Rear Diff Unit
38410AA120 - 2006 Rear Diff Unit
38410AA140 - 2007 Rear Diff Unit

NOTES: 04 and 05 are the same. I have taken an 04 Diff apart, and rest assured it is clutch pack based. 2006 had a new rear diff, as did 2007.


Front Diff

38410AA060 - 2004 Front Diff Unit
38410AA100 - 2005, 2006, 2007 Front Diff Unit

NOTES: Sure enough, the 04 US 6MT had a Suretrac front diff, as the 060 part number is also used in the Version 8 JDM 6 Speed ( C, D ). 05, 06, and 07 all have the same front diff.


Center Diff (DCCD)
38913AA160 - 2004, 2005 Center Diff Unit
38913AA190 - 2006, 2006 Center Diff Unit


NOTES: 04 and 05 has the same center DCCD unit, which was upgraded in 06. The center diff used in all cases (160 and 190) are the same as used in the JDM 6 speed of the same years. AA160 was used in C,D, and E JDM 6 speeds, and AA190 was used in F and G.
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Old 03-13-2007, 10:01 PM   #37
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Bump, i would really like to knnow about this
Quote:
Originally Posted by Skoobie View Post
What will a 2 way center diff do in an all wheel drive? Specially with a 1.5 front and rear.
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Old 03-14-2007, 02:13 AM   #38
sponaugle
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Here is a quick look at all three diffs in the US cars.



JDM and EU coming.

Jeff Sponaugle
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Old 04-25-2007, 12:34 PM   #39
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Quote:
Originally Posted by kingsubi View Post
Just to add here that the 20Kg/mm center is not a very street friendly at all
How does it drive on the Street? I guess you mean by wheel hop on turns or binding?
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Old 04-26-2007, 01:56 AM   #40
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Default Subaru Center Diff

Dear friends
I am writing from Greece, so please forgive me for my poor English. I need your help, i see you know many details about diffs!
I am rallying in Greece (Gravel Rallies) using a Prodrive Impreza N8 2002. Recently my center diff has been broken. It is an " Early Grey 2001" one, named by Prodrive. I have searched to find a rerpair kit, there is no availability worldwide. So i decided to buy a brand new "Golden'' (named by Prodrive) one, Part No 38913AA190. Alternatively i can find a 38913AA160 too. The problem is that a Subaru Technician-friend of mine- told me that this new C.D will blow up if i will use it with my curent ECU ,which is The Pectel-Prodrive one. And he told me also that it may work properly connecting (interfering) on the C.D. leads a resistance (resistor).
Is this correct? Do somebody Knows something about? Please help me,replying here or by Email at x-platis@otenet.gr.
Many thanks in advance
Platis.

Last edited by Platis; 04-26-2007 at 07:15 AM.
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Old 04-26-2007, 06:49 PM   #41
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I am a scooby newbie. So i cannot send by Email my questions to Unabomber. Please could somebody do this for me?
Thank you
Platis
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Old 06-10-2007, 01:21 PM   #42
Menik
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Quote:
Originally Posted by Platis View Post
Dear friends
I am writing from Greece, so please forgive me for my poor English. I need your help, i see you know many details about diffs!
I am rallying in Greece (Gravel Rallies) using a Prodrive Impreza N8 2002. Recently my center diff has been broken. It is an " Early Grey 2001" one, named by Prodrive. I have searched to find a rerpair kit, there is no availability worldwide. So i decided to buy a brand new "Golden'' (named by Prodrive) one, Part No 38913AA190. Alternatively i can find a 38913AA160 too. The problem is that a Subaru Technician-friend of mine- told me that this new C.D will blow up if i will use it with my curent ECU ,which is The Pectel-Prodrive one. And he told me also that it may work properly connecting (interfering) on the C.D. leads a resistance (resistor).
Is this correct? Do somebody Knows something about? Please help me,replying here or by Email at x-platis@otenet.gr.
Many thanks in advance
Platis.
I would ask prodrive directly, they're surprisingly helpful: enquiries@prodrive.com
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Old 08-01-2007, 07:13 PM   #43
impreza_GC8
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Very informative writup, thanks! Just one thing I noticed that wasnt addressed however (and the reason why I was searching this thread in the first place).
I read an article on Differentials that stated that Viscous-type Diffs begin to lose their LSD coupling ability after 60,000 miles or so due to degradation of the viscous fluid. If this is true, my RS has 83,000 miles on it, so my rear LSD is acting more like an open diff than it was when it rolled off the dealer showroom in 2000. This is worrysome to me, so is it worth replacing to a gear-type LSD that wont wear out after 60,000 miles? Thanks.
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Old 08-01-2007, 07:49 PM   #44
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Sounds bogus to me. The visous fluid is silicone and silicone does not wear out. I could be wrong, but I don't think so.
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Old 08-02-2007, 01:43 AM   #45
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EVERYTHING wears out eventually, but I have no clue what the operational life of a vlsd unit would be. Well... when I tried hand-turning rear wheels with my 90k mile vlsd diff... the wheels spun in opposite directions and felt exactly like an open diff, but who knows? I have a clutch-type now... Love it love it, but it is really clunky when making sharper turns and has enough bite to sometimes chirp a tire during tight parking lot turns. And all this even using actual subaru LSD oil (even came in a blue can with all kinds of japanese characters on it and almost no english).
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Old 08-02-2007, 09:23 AM   #46
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As I understand the VLSD, you in fact "should" be able to turn the wheels by hand. the limited slip coupling doesn't kick in until the fluid heats up enough to lock the sides. I don't think turning by hand applies enough force to heat up the fluid. Or am I way off here?
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Old 08-02-2007, 11:49 AM   #47
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From how I understand the principle, your theory is correct. I mentally imagine it as wizards and elves, but smart people say silcone fluid heats up and fills grooves, then *insert magic event here* and your LSD is a real LSD.
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Old 08-02-2007, 02:14 PM   #48
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That is why a VLSD sucks! You have to have a wheel spin (not just slip) for it to even start to work.
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Old 08-02-2007, 02:22 PM   #49
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You'd think there would be enough preload/friction/drag/etc. there to at least get the other wheel to turn in the same direction though... I guess not.

However vlsd works, it was slow to react and when/if it did it wasn't particularly noticable. I could never get the tail out with my vlsd, even in the wet, and never wanted to risk hitting the e-brake and stressing the center diff... With the clutch type, it's just a matter of some streering wheel rotation + some added throttle, and whoa I'm going sideways! Absolute day and night difference.

Last edited by jhargis; 08-02-2007 at 02:29 PM.
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Old 08-02-2007, 02:49 PM   #50
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That is how my Suretrac is. Steps the rear right out The cusco center diff helps too.
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