05 wrx rear diff in obs?

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kblood477

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I have been reading that the final drives of wrx and my obs are 3.900 is this true . trying to swap in the lsd into my car and want to make sure I don't mess something up big time

 
kblood477 said:
I have been reading that the final drives of wrx and my obs are 3.900 is this true . trying to swap in the lsd into my car and want to make sure I don't mess something up big time
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The WRX tranny is 3.90. but the rear diff is 3.54. There is a reduction in the transmission that allows this in the WRX, so no, you cannot run the WRX rear diff in your OBS, it will not match up.

 
IBratmanI said:
The WRX tranny is 3.90. but the rear diff is 3.54. There is a reduction in the transmission that allows this in the WRX, so no, you cannot run the WRX rear diff in your OBS, it will not match up.
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This is correct 100% the answer. The center diff ratio is different in the wrx stepping the rear down to 3.54. Last time it came up I missed that info in the center diff column of the chart
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Where is that info? What is the reduction? The center diff? The output shaft? I don't understand how a final drive can be 3.90, but its not 3.90.

There are cases on NES of 05 legacy turbo lsd rear diff going into NA 06 legacy. Why would they reduce a 390 to 354 in the Imprezas?

So ya Jason I have heard people mention what you said before but I have never seen any of the actual facts about these claims. I'd like to figure out the specifics of it all. Also wondering if that is model year specific (like 02-04 2.0L only?) or if all I need to do is swap output shafts or center diffs? If I swap center diffs then I'll have to do front diffs.

It just seems like Subaru would make things the same as much as possible to keep costs down, like final drives and rear diff guts.

I have a 2.0LWRX rear diff, and I have a 2.5L NA rear diff. Whats going to be different? The number of teeth on the ring and pinion, right? Guess I'll have to count them one of these days.

 
Bryan linked the transmission chart in post #2. I've seen a couple different charts and they all seem to notate that.

Here's the WRX section of the chart:

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The transmission ratio is notated as being 1.1

Why it's like that, I don't know.

I haven't dealt with wrx boxes and diffs, so I can not verify this information as correct.

 
They probably have a non-1:1 center transfer gears to put less torque on the center diff, or something like that.

But everyone saying 3.54 are correct. Same as the SVX and 5eat... so you can swap those diffs.

 
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