JDM viscous diff swap
 

Is the JDM viscous rear diff a "plug-n-play" swap with the US open diff. I know the JDM diff is 3.7 ratio and not 3.545 like the US. Just curious or does this require an entire JDM tranny/front diff as well?

Re: JDM viscous diff swap
 

all SVX's have an LSD rear diff.

Re: JDM viscous diff swap
 

But didn't the JDM SVX only get the viscous LSD? I thought the LSD we got was non-viscous?

Re: JDM viscous diff swap
 

If our LSD is not viscous, what type do you think it would be?

I've not heard of too many other LSD's that aren't viscous in some way.

(I don't mean to be condescending with this post, I'm interested in this idea).

Now the type of coupling in the transmission on the other hand - that's a different story.

Re: JDM viscous diff swap
 

The US and JDM VLSD diffs are identical, except for gear ratios. If your front diff is 3.545, use the US rear diff. If you install a fwd 3.70 front diff, use the JDM rear diff,,, :)

Re: JDM viscous diff swap
 

Your XTs have a mechanical LSD rear diff.
I believe the automatics were 3.70, but the diff is not compatible with SVX axles.

Re: JDM viscous diff swap
 

There are viscous LSDs, friction clutch LSDs, and helical-gear torque biasing LSDs. Torsen is an example of the helical gear type. 2007-2009 Legacy Spec.B uses a torsen with 3.9:1 final drive, where the 2005-2009 Legacy GT have viscous LSD rear differentials, and a 4.11 final drive. My 99 miata has one, as well.

I believe the Spec Bs with the 6MT gearbox use a 1.1:1 step-down, with a 3.9 rear diff, and a 3.54 front diff (same as SVX front and rear, with no step-down), and the Spec B rear differential can be pieced together with the SVX diff carrier system, and can be used in an SVX, with the corresponding 6-speed manual conversion. But don't treat that as an iron-clad guarantee... I am not 1000% positive it works exactly that way.

The Spec.B driveline is basically the same as the later model WRX STI drivetrain, except without the driver-override center differential DCCD system, it is basically set to permanent "auto" on the center differential control, and the Spec B didn't get WRX STI's Brembos nor 5x114.3 wheel hubs, and retained the Legacy GT's power level and turbo configuration, rather than the STI's hotter turbocharger, and requisite intake and intercooler setup.

Personally, my ideal SVX would have a tuned-up and freshened EG33 engine, somewhere around 300 naturally aspirated horsepower, or a bit better, backed by the Legacy Spec.B drivetrain... both the 6MT manual transaxle, and torsen rear differential, and the rearward standard torque distribution, with Variable Torque Distribution center differential. My ideal new Subaru would merely transplant the EG33 with a new EZ-series, tuned and equipped similarly.

Otherwise, in general, there are newer systems that couple differentials with electronically controlled clutch packs that actively manage the output of differentials, which is basically the same as the VTD center differential Subaru system I just mentioned, also like the rear diff in Acura RL's SH-AWD, and such. I believe that other torque-vectoring electronically managed differentials, like Ferrari, and now Audi, and others are starting to use, are similar systems, with varying degrees of sophistication.

Re: JDM viscous diff swap
 

My LS has a Torsen as well :D

Re: JDM viscous diff swap
 

If its a 3.9 Torsen, one could assume it would be useful in any 3.9 equipped car - say a legacy/imprezza 5spd, not just the 6speed from the leggy.

Correct?

This could be a option worth looking at, perhaps for the aftermarket options of a 3.9... assuming the axles fit the leggy rear end.

That is to say, rather than an R180, those of us with a slightly older imprezza tranny could have a pretty beefy rear end, without having to do the STi/WRX tranny for alot more!

Re: JDM viscous diff swap
 

The Spec B Legacy has a 3.545 R180 rear diff with Torsen center, same ratio as 2007+ STI, if I have the changeover year correct. You will need STI axles to use in the SVX. :D

Re: JDM viscous diff swap
 

Don't mean to be picky... but I looked up the Spec B's final drive ratio before I posted the above information, and it is 3.9:1, down from Legacy GT 5MT's 4.11:1 There is a bias-gear in the transaxle that creates a 65% standard rear torque bias, and I am under the impression that the front and rear differentials do not have the same final drive ratio, due to that bias, that the rear is 3.9 and the front is 3.545...

The rear differential casing design is of the R180 type, with a 3.9 ring gear, and a torsen limited slip unit. The ring and pinion gear are usually separate parts from the differential mechanism inside, the ring gear bolting to the differential/limited slip unit. The torsen differential in it should be compatible with any R180-specification differential, and any of the available R180-compatible ring and pinion sets should bolt to it, and work inside that differential case. It likely does require the inner axle stubs to be the same specification as an STI or Legacy GT Spec B in order to work, if they are different than R160 or other rear differential specifcations.

I am not sure, but I think that most Subarus aside from the Spec B and STI, including the non-Spec.B Legacys, and the SVX use an R160 type rear differential in stock configuration. Other higher powered RWD japanese cars, like Nissan Z cars, I believe used an R200 or higher specification rear differential... likely from a common supplier and a modular scaleable design, but that doesn't mean that parts can necessarily swap, as they are likely different sizes. It would be like trying to fit Ford 8.8 hardware into a 9-inch differential, or GM 10-bolt hardware into a 12-bolt case, or Dana 44 hardware into a Dana 60... and so on...

In the Spec.B's case, I am pretty darn sure that the torsen differential is in the rear diff, and the center differential is an electronically controlled clutch-pack arrangement, that can vector torque forward or rearward, and is the same unit as a WRX STI's center diff, minus the driver-control switch bit, as if an STI was permanently set to the Auto setting, and is also a similar system to the Variable Torque Distribution center diff in the 5EAT transaxle. There may be a torsen/helical gear differential as the mechanical "guts" of the VTD center differential, but there are also torque vectoring clutches involved to make it a "Variable Torque Distribution" system.

But I will stand corrected if the documentation shows otherwise... But this has been a topic of my research and many a discussion regarding the differences between the Legacy GT 5-speed (which I have one of), and the Spec.B 6-speed, when it came out in 2007, and since.

Re: JDM viscous diff swap
 

I looked it up too :) I have a Spec B rear R180 Torsen diff :cool:
I pulled the cover a long time ago, it is 3.545, and the center is clearly Torsen. The Legacy diff covers have long studs like the SVX, the STI diffs have the short studs. STI diffs have temp sensors, Spec B does not.

I believe that all Subaru factory-equipped R-180 Torsens have 3.545 gears. To my knowledge, all non-Tribeca Subaru rear diffs are R160, said because, I am not familiar with the Tribeca diffs. I'm not sure about 3.272 Legacy GT either,

I believe you have your facts backwards, the front diff is 3.90, the rear diff is 3.545

The Torsen center WILL NOT bolt onto any R180 ring gear, only those manufactured after about 1986. The Torsen center should bolt into any Subaru installed R-180 rear diff. I built a R180 4.444 Torsen for example :D.

Pre '86 diffs, R160 included, had smaller diameter ring bolts.

Post '86 R-180 centers require larger diameter axles than R-160s.

Re: JDM viscous diff swap
 

I'll take an informed word for it, and thanks for the info. I do actually like to get more credible information than I already have. Thanks.

I still want a Spec.B drivetrain in a A-1 shape SVX... :D Too bad the Legacy's interior features (love the EL gauges...) or front end bodywork can't be incorporated as easily into an SVX as driveline hardware.

Otherwise... I wish Spec Bs were painted other than gray tones... I like garnet red and regal blue pearl, and would pay to trade for World Rally Blue, if it had ever been offered on this side of the pacific ocean.
but I sometimes do wish I had the additional features that the 2007-2009 Spec B has, and the 2006 Spec B's red leather seats... over my 2005.

Re: JDM viscous diff swap
 

No offense taken, I am learning more about the mechanical aspect of our cars, thus why I asked.

I was the VTD tranny that the JDM market got(duh this is what I was thinking about in the original post)

However,

Need for Speed- you say the US fwd svxi got the 3.7 front diff? So If I sourced one of these and a JDM rear diff the swap is do-able?

Just trying to figure this out. Thanks for all the info guys! Wow that is some serious homework!

Re: JDM viscous diff swap
 

Swapping front diffs is very do-able, probably a thread here about how to set it up properly. We swapped a 4.11 diff onto an eSVX trans, and many have found it necessary to swap another 3.545 diff for a broken diff. Do a search, should be helpful. Why not replace a broken 3.545 front diff with a fwd 3.70 diff, since you have the right rear diff?