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Old 08-04-2007, 03:46 PM   #51
keaniegenie
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Quote:
Originally Posted by Crazykev View Post
That is how my Suretrac is. Steps the rear right out The cusco center diff helps too.
Whoa Kev, haven't seen you here for a while!

I'm also in the market for a center diff.

I've heard from other transmission specialists that a 20kg center will induce UNDERSTEER, which seems to be the opposite to what Unabomber says on the FAQ's. I got this info from Dave_Clark, the tranny guru who helped bring RA's to the US before we had any other gear option.

I now have a cusco 1-way front and a 1.5 way cusco rear. I want a better center diff that will work better than stock and still work good for daily driving in all climate conditions. DCCD, right? Has to be a 5mt diff though. The JDM ones are expensive, hard to find, and would be a pain to replace if it went bad. The Cusco one is nice but not ideal for all climate conditions.

I'm leaning towards a helical center. What do you guys think?
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Old 08-06-2007, 01:04 PM   #52
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I'd think that with LSDs front and rear, the tarmac would be pretty cool. I like the larger torque distrobution to the rear, but then again, I come from the world of mostly RWD european cars, so I guess it's all relative.
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Old 08-06-2007, 08:18 PM   #53
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Quote:
Originally Posted by jhargis View Post
I'd think that with LSDs front and rear, the tarmac would be pretty cool. I like the larger torque distrobution to the rear, but then again, I come from the world of mostly RWD european cars, so I guess it's all relative.
I do too. From what Crazykev was saying, the key to the 65/35 split tarmac is a good rear diff since it's mostly a RWD car.

Once in a while, I'll get somebody who tells me their DCCD defaulted to 65/35 is a horrible setup and that you can spin the car out. I'll believe them for 2 seconds before I remember I've driven RWD cars, and spinning out a 65/35 car means the person isn't used to driving RWD cars!

Maybe I should do more research and become the NASIOC LSD guru.
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Old 08-06-2007, 08:18 PM   #54
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If I did it all over again, I would go with the helical center diff. It didn't exist when I swapped in the Tarmac diff. I missed it by a couple months

Haven't been around for a while. Built a new house and had my third little girl, so I've been sooo dang busy.

Just swapped back to an ACT organic clutch last weekend. That Spec Kevlar sucked!!! Lasted 15K

By the way guys, you don't have to pull any suspension stuff apart to get the trans out. Slide it past the studs at the bottom and you can pull the CV axles right out. I hate bustin' out ball joints or messing with the strut bolts.
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Old 08-06-2007, 08:25 PM   #55
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Quote:
Originally Posted by keaniegenie View Post
I do too. From what Crazykev was saying, the key to the 65/35 split tarmac is a good rear diff since it's mostly a RWD car.

Once in a while, I'll get somebody who tells me their DCCD defaulted to 65/35 is a horrible setup and that you can spin the car out. I'll believe them for 2 seconds before I remember I've driven RWD cars, and spinning out a 65/35 car means the person isn't used to driving RWD cars!

Maybe I should do more research and become the NASIOC LSD guru.
I love the rear bias! Stinks in the snow and sometimes in the rain, but it's fun The car never feels like it's going to spin out though I'm with you Keaniegenie, I came from RWD myself.

I also change my rear diff fluid every 10K now being that it's under so much strain. Someday I'll swap to an R-180.
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Old 08-25-2007, 08:23 PM   #56
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Regarding the STI R180. Is the plug with the temp sensor in it also where I would fill it?
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Old 08-25-2007, 08:29 PM   #57
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Have any of you guys driven on a helical center diff? How does it compare to stock or DCCD in an STi.
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Old 02-05-2008, 12:00 AM   #58
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I had a question. what happens to the differential in a WRX (NOT STI) when the e-brake is applied? i no STI's are capable of pulling the e-brake (parking brake) because of their different differential design. But, what happens with the viscus center or rear diff when the e-brake is pulled while moving to put the car into a slide for quick turn around?
Thanks
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Old 02-05-2008, 01:18 AM   #59
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you can always just step on the clutch when you yank the ebrake, and give it gas to keep the rpm up, downshift to a gear that corresponds to your speed, then step off the clutch on exit, and gas it. thats one of the things i do for a power slide. For your quick turn around: step on the clutch. I know this doesnt answer your question but i hope this helps somehow; cheers
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Old 02-05-2008, 09:17 AM   #60
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Pulling the hand brake in a wrx = BAD. It gives the front and rears a big difference in rotational speed while the center diff is trying to keep them equal, this can end up overheating and frying your viscous center diff.

I don't think stepping on the clutch while pulling the hand brake will do anything. The viscous center diff will still be keep the front and rears connected and trying to turn them at the same speed. Correct me if I'm wrong.
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Old 02-05-2008, 09:45 AM   #61
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true, the center will try and keep the power split 50:50, but the way i see it (which i could be wrong) its a lot better to clutch it tha have it engaged, with all that power running throught the drivetrain trying to turn the wheels, making the center work really hard. Think of the car on a lift, and spinning the tires on neutral you can spin the wheels either way, compared to having it on gear which is trying to go one way. I think i took a step to the left on the main topic here
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Old 02-05-2008, 06:56 PM   #62
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bump for more info im interested
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Old 02-07-2008, 09:01 PM   #63
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bump for anything?
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Old 02-07-2008, 09:52 PM   #64
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like anything, the harder you use it, the faster it will go out, sorry but im not exactly familiar with the mechanical break down of it while its in work. Hopefully someone thats more knowledgeable on this topic can help you out. Have you tried the all mighty google for answers?
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Old 02-08-2008, 11:56 AM   #65
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Its already been answered...handbrake use on a WRX is bad. It can explode the center diff due to too much force and heating up of the fluid. Once or thrice may be fine for some fun, but repeatedly doing it...not so good.
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Old 02-11-2008, 08:00 PM   #66
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This is for Unabomber or anyone qualified to answer the question. But how would one tell if they had blown there center diff. I have several threads about this problem out right now, but over the summer I pulled my e-brake (parking break) once while playing in the rain. When I pulled the brake there was a violent thumping/ hopping feeling as I slid to a stop. I drove home fine but when turning into a drive way the first symptom of binding viscous couple occurred (binding/ hopping of the car). After a few circles, it unbound itself and seemed to drive fine until aggressive cornering again, (a slide in snow or on pavement, NO full cranking of the wheel right or left). The car drives fine in normal daily driving turning and going straight. But recently when the front and rear diff fluids were changed to check for metal shavings I found the fluid to be very dark. Ever since being changed all I can smell is burning diff fluid, even after 111miles. Are there any other ways that might suggest I have in fact blown my center diff before I tear my diff apart?
Thanks
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Old 02-11-2008, 08:55 PM   #67
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I too have a quick question... Is there any way to put the sti's DCCD in a WRX tranny?
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Old 02-18-2008, 08:01 PM   #68
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Got a simple one for you guys..

where is the center diff in a regular Impreza (2008 2.5I)...

I'm about to buy that car and was just wondering where it was... I've read that it's enclosed in the gear box... but...

where :


If it's in there, the only place I can think of : the output shaft is hollow inside ... Am I right?

I've tagged the gears and input output shaft..

Something like :

Because I'm really good at drawing :
Red : Hollow Output shaft and center diff
Blue : inside shaft for read and front...
Yellow & Green : viscous disks...
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Old 02-18-2008, 08:20 PM   #69
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Quote:
Originally Posted by llavalle View Post
Got a simple one for you guys..

where is the center diff in a regular Impreza (2008 2.5I)...

I'm about to buy that car and was just wondering where it was... I've read that it's enclosed in the gear box... but...
The transfer case attaches to the rear of the tranny left side of your picture

This is what it looks like...29 is the center dif

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Old 02-18-2008, 09:12 PM   #70
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Thanks

I was looking for an exploded view just like this one!
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Old 02-18-2008, 09:46 PM   #71
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Alright, here's another one...

Possibility 1) In that case, that wouldn't be call "Symmetrical AWD"..
If the viscous coupling unit is "plugged" at the rear of the transmission like it appears to be in your image(between the transmission and the driving shaft), that means the following :

1-Front wheel are ALWAYS turning at the same speed as the driven shaft
2-Rear wheel are connected to the driven shaft by a viscous coupling
Driven shaft = lower shaft in the picture I posted.

That means that, if I floor it when I'm on ice(4 wheels on ice),
1-The front wheel start to spin
2-Since the transmission side of the coupling is turning faster than the driving shaft side, the viscous coupler reacts and start turning the the rear wheels
3-All 4 wheels spins



Possibility 2) More plausible, that is a 50/50 symmetrical drive

More something like : (the drawing is right, it's the colors I'm unsure about)

Mauve Color : Input from engine, travels by the gears to the green shaft
Green : Hollow shaft connected from the gears to the central diff
Blue : pinion shaft connecting the front side of the diff to the front wheels
Red : Gears(probably a reduction of the outout speed to lower the driving shaft vibrations) and shaft connecting the rear side of the diff to the rear wheels.

Is that right.. I'm unsure about the hollow shaft with the pinion shaft going through... Can anyone confirm this...

1-Hollow shaft is always spinning at the same speed as the diff casing
2-Front wheels are connected to one side of the diff
3-Read wheel are connected to the other side

That means that, if I floor it when I'm on ice(4 wheels on ice),
1-All 4 wheels spin... if traction is equal on the 4 wheels.. and if you don't take into account the inertia of the driving shafts, joins, etc etc.


Which one is right?? I'd go with #2.. am I right?
I'm talking about a regular Impreza... manual transmission( I know the automatic isn't using a viscous coupler... but it should look almost the same)

Last edited by llavalle; 02-18-2008 at 11:11 PM.
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Old 06-04-2008, 01:08 PM   #72
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Quote:
Originally Posted by sponaugle View Post
Here is a quick look at all three diffs in the US cars.



JDM and EU coming.

Jeff Sponaugle
Does 41:59 imply something about the differential ratio?
If not, what is the diff. ratio of the '07 STI Torsen rear diff?
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Old 06-04-2008, 02:06 PM   #73
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looks like the adj available for forward/rearward bias of the center diff
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Old 06-04-2008, 05:06 PM   #74
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You know, I didn't even notice that it was under the center diff. column, my mistake. But I bet you're right.

I think I've determined that the '07 STI will have a 3.90 rear diff ratio, still not 100%.
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Old 08-13-2008, 01:06 PM   #75
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So what info is available for the helical center diff? So far I've only heard of limited options for the 6-speed center.

<-- has a non-dccd JDM transmission with the suretrac front diff.

Since I autox and track I was planning on the cusco rs 1-way front and 1.5-way rear, but was thinking of leaving the center alone for now. But if there's an option I'd like to research it!
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