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Old 01-10-2003, 05:41 PM   #1
jasona
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Default lsd ?'s

i have an 02 2.5ts. as you may or may not know, this has an open rear differential. i want a limited slip, and the cheapest way to get one would seem to be swap in one from an rs or wrx. but the rs and wrx have a 4.11 final drive and the ts has a 3.9. now, i like the 3.9, so how would i go about changing an rs/wrx rear diff to the 3.9? and what do i need to swap it into my car, it should just about bolt up right?
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Old 01-10-2003, 05:43 PM   #2
jeffg
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I was pretty sure the WRX had a 3.90, not a 4.11

I could be wrong though.

J
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Old 01-10-2003, 06:14 PM   #3
jasona
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oh really? can anybody confirm that? that would be good.
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Old 01-10-2003, 06:41 PM   #4
RebelINS
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While it is true that the WRX has a final drive of 3.900, it also has a drivetrain reduction ratio of 1.1:1, so the rear diff is actually 3.545:1. To change gearing, you would need a new ring and pinon for it which cost like $350 or something, plus you would have to install it, which might be difficult depending on how good you are at working with gears. There might be other cars that have an LSD 3.900 rear diff though. I am not 100% sure, but I thought that the SVX had a 3.900 final drive, but don't take my word for it. Some WRX type RA's have a 3.900 final drive, and some Impreza Turbo's and GT's have them, but these would all be harder to source.

-Wes
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Old 01-12-2003, 12:42 PM   #5
akoshy
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Quote:
Originally posted by jeffg
I was pretty sure the WRX had a 3.90, not a 4.11

I could be wrong though.

J
The manual WRX has a 3.90 and the Automatic WRX has a 4.111
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Old 01-12-2003, 05:42 PM   #6
jasona
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ah that explains it, cuz i could have sworn i saw 4.11 somewhere. thanks.
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Old 01-13-2003, 06:22 AM   #7
wawazat
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Quote:
Originally posted by RebelINS
There might be other cars that have an LSD 3.900 rear diff though. I am not 100% sure, but I thought that the SVX had a 3.900 final drive, but don't take my word for it.

-Wes
Sorry, but the SVX uses a 3.545:1 front and rear ratio. The Legacy Turbo uses a 3.900:1 LSD rear diff. I have one in my garage. Other USDM Subaru vehicles (certain Outback Sport and Legacy L's) use the 3.900:1 ratio as well, they are not LSD however.

Todd
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Old 01-15-2003, 01:29 PM   #8
1.8L
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Hello,

It doesn't matter if the diff you are looking at is LSD or not. All you need, used, is the housing and the gears. The diff unit itself is interchangeable on all Subarus since the late '80s, I believe. They're all that famous R160 diff. So get the drive ratio you want and move an LSD into that setup.

Joel
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Old 01-15-2003, 01:57 PM   #9
Jaxx
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?
joel will the output shafts work if you do that?
don't you have to know how to shim a dIff to do this?

i was under the impression that
the TS has a 4.11
the RS has a 4.11
the WRX auto has a 4.11
the WRX 5speed has 3.xx (whatever it won't work)
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Old 01-15-2003, 02:08 PM   #10
1.8L
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Hello,

Okay, so I was a tad simplistic. Each type of diff unit uses a different axle input stub. You have two choices. First, and the one I went with, is that although all the various axles for the R160 are different lengths, the amount of difference is so small as to be unimportant (a couple millimeters). I simply switched axles to a set that would work with the diff.

The other choice is what we did on the racecar. We switched diffs and then we took the inner CV apart on the alxes and switched the inner most section. That way, the proper stub matched the diff and the axle length was retained.

Now, it's been a few years, so I'm not sure I remember this all correctly, but all the open diffs use the same axle ends. All the VLSDs from the US use one set of axle ends. The mechanical diffs - ie, some of the Japanese diffs - use a third axle end. Since Mike Shields did a wonderful job convincing KAAZ USA that the WRX has a mechanical, Suretrack rear diff, even though it does not, they do not yet carry a rear KAAZ that works with US Spec Axles. So you have to use the mechanical diff style axles with a KAAZ.

Now, to bring the discussion back, if you have an Impreza that does not have an LSD, and you want to add an LSD, but you can only find rear diff housing units of the wrong ratio, then you can buy that wrong-ratio setup along with the alxes that came with it. You then take off the rear cover of both diffs, pull out both melons, swap the ring gears on both melons, and reinstall your ring gear into your housing, with the LSD melon now in it.

You now have a spare open diff and axles of the "wrong" final drive ratio.

As for shimming, yeah, in theory you would need to shim the diff properly. You might just go pick up some of that goop and test your new setup, but in the half dozen swaps I've done, using a factory melon always makes the setup work right. In fact, we didn't have to adjust the shims on the racecar when we switched the rear to a KAAZ from the stock VLSD. So I wouldn't worry about it too much. Check it to be sure, but then be done.

Joel
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Old 01-15-2003, 02:11 PM   #11
1.8L
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Hello,

Oh yeah, there is one caveat. A diff melon designed for use in the WRX housing will not fit in an Impreza housing as is. If you look at your WRX housing, you'll see two die-grinder looking marks in the housing. The factory did a pretty quick and dirty job here. They ground away about a millimeter of housing to get the diff to fit. You would have to do the same to get a WRX melon into your housing. It sounds scarry, but if you have both in front of you, you'll see that the die grinding is very minimal. If you're afraid, bring it to any metal shop and they'll probably do it for less than $20. Maybe even just for a 6-pack of beers. I know I would make that trade, if you're in the Bay Area.

Joel
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