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Howdy everyone,

It's 2 months or so and counting until i get my 08 WRX. I'm a noob so any feedback is welcome about this and any topic. My question is this:

Does the 08 WRX come with limited slip differentials or not? Also, if it doesn't, where would be a good place to get some? Is the VCD considered a limited slip as well?

-Z-
 

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Re: VCD and Limited Slip?

No LCD this year and yes the VCD is considerd a type of traction control along with a y-x axis control. Some like it others dont.
i've been told we have LCD's in front and rear. and it seems like we do cuz in snow conditions i have never exp. 2 wheels on pavement and the other 2 on snow and the wheels on snow spinning like crazy which i see alot of 4wd trucks doing because they are not limited slip
 

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Re: VCD and Limited Slip?

with the traction control (VDC?) off all 4 of my wheels spin....

but the VDC being on ... if you floor it on dry pavement around a roundabout for example... the resulting accurate directional control is AMAZING.

I leave the VDC on unless I'm trying to go fast or trying to purposely get sideways (dirt/snow/gravel).

I think it's alien technology from Japan.
 

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the VDC works extremely well on the track too. Just turn your steering wheel, and see your car turn for you.
 

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it's really amazingly simple... it uses the same concept as army tanks for turning (it puts more power to the wheels opposite of the direction you're turning to "rotate" the car... or "cuts power" to the other wheels depending on how you look at it ... glass is half empty half full kind of thing)
 

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Yup. So in a traction scenario, like the one stated above, LSD = the tire with the friction gets the torque, VCD = Tire without the friction gets the brake. VCD is a Systems Scientists wet dream in action.
 

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well...

less of a "gets the brake" and more of a "gets no power / goes neutral"

brake would make the problem worse...

TCS cuts power.

braking is what the ABS system does.
 

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well...

less of a "gets the brake" and more of a "gets no power / goes neutral"

brake would make the problem worse...

TCS cuts power.

braking is what the ABS system does.
Kind of. "ESC uses a hydraulic modulator to assure that each wheel receives the correct brake force. A similar modulator is used in ABS. ABS needs to reduce pressure during braking, only. ESC additionally needs to increase pressure in certain situations."

"The controller computes the needed brake or acceleration force for each wheel and directs via the driver circuits the valves of the hydraulic modulator."

So the VCD system uses this hydraulic modulator, similar to the one used in the ABS system, to apply breaking force to individual wheels. What I'm trying to get at is that LSD uses torque to make the car more stable and VCD uses breaking force at individual wheels to make the car more stable. It can indirectly use torque but only by increasing the engine output and "sending" it to the wheels that need it by breaking the ones that don't.

edit: "What I'm trying to get at is that LSD uses torque to make the car more stable and VCD uses breaking force at individual wheels to make the car more stable." I'm still having trouble saying what I mean haha. LSD can directly manipulate torque. VCD manipulates toque by using the braking system.
 

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yeah but what I was saying it's more of a neutralizing power (think "slowing down" braking you do when coming to a stop sign) than a slamming on the brakes really fast like ABS does.
 

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The new WRX only has a viscous locking center differential. I believe the previous-generation WRX had that in addition to a rear Limited-Slip Differential.

ABS pulsates the brakes when the system senses any of the wheels locking up (typically the rears).

Traction control temporarily cuts off engine power and can (and will) individually apply braking power to the necessary wheels in order to maintain the driver's intended course.
 

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This is was my response to a similar question in the 'General Aftermarket Talk & Technical Questions \ Subaru Impreza Technology Forum':

OK so it is my understanding that the 08 WRX doesn't have a Limited Slip Differential but it does have stability control and traction control.
So my question is with the little VDC TC button turned off what stops all of the power going to any one wheel. There obviously is some other type of differential but does it control slippage.
Also what are the pros and cons for having only VDC TC over a LSD and didn't the 07 have both?
All AWD Subarus have a limited slip diff (of some sort) in the center. Non-STI manual transmission cars have a traditional center differential that has a viscous locking component to transfer power once slip occurs. This viscous unit is only ever called upon when there is a significant difference in speed between the front and rear axles.. such as when one end loses traction. When there isn't any slip.. the differential acts normally and distributes the torque 50/50 (f/r). Since it's very hard for a Subaru to spin wheels on pavement with this configuration.. the viscous portion of the center LSD does nothing 99% of the time. Off-pavement and in extremely slippery conditions, the viscous LSD keeps the front and rear axles turning at roughly the same speed whenever possible. So.. even with the VDC turned off.. the center LSD is still working to make sure you have power going to at least two wheels. ;)

Most Subarus have had open front and rear diffs... yet, they're still notorious for being unstoppable snow machines. In the US, the Legacy 2.5GT, some Legacy Outback models, 00-01 2.5RS, 02-07 WRX and STI have all had a limited slip rear differential. Except for the STI, this rear diff used a similar setup to the manual transmission's center LSD.. with a viscous slip-limiting unit working in conjunction with a traditional differential. Just like the center viscous unit, the rear LSD doesn't do anything when there's decent traction. Under power, the rear axle has more traction as weight transfers to the rear.. as such, a Subaru is more likely to lose traction on a front wheel in higher grip situations rendering the rear LSD useless for most performance applications. The rear LSD does make the rear of the car easier to 'kick out' on loose surfaces... but, as a side effect it can also make the car more twitchy on snow and ice.

As for the pros & cons of having only VDC over an LSD... well, as I mentioned, the rear LSD can make the rear of the car twitchy which doesn't usually sit well with something designed to make the car more stable. In addition, the TC can do a better job of taming a slipping rear wheel than a viscous LSD can.. and it can still transfer torque by braking the slipping wheel.

No, the '07 Impreza did not have VDC or TC of any sort. This is a first for the Impreza.

FYI: The STI still has mechanical limited slip front, rear and center diffs that are more predictable, progressive and smooth than the viscous LSDs.. so they probably work better alongside the VDC.
 
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