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Old 06-04-2003, 04:28 PM   #1
serious
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Default wrx rear differential in a legacy?

Hi all, i'm wondering if the 02 wrx 3.90 differential will bolt right into my 96 legacy? I think i read somewhere i would need the axles too as there not the same? Would i need the hubs too or just the axles?
Anything else needed to convert?
Thanks
Brent
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Old 06-04-2003, 05:34 PM   #2
Jaxx
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just the axles .. but .. only the WRX wagon/legacy turbo/2000-2001RS axles wil fit as the WRX sedan are longer ....


although stimpy has come up with some findings that may contradict this

the diff from the manual WRX is not 3.9 it is 3.54
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Old 06-04-2003, 05:57 PM   #3
stimpy
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I don't know if it was an accident or what, but the front axles do not list lengths in the FSM; just the rears. Going by that logic, the didn't feel the need to specify the lengths since they would be the same. Diameters etc are still listed since they are different from the RS and the WRX. Seems really weird that the front axles would be the same length between sedan and wagon. One of these days I might call the dealership and have them run a part number check.

The lengths of the rear axles are explicitly mentioned in the FSM though. The rear axles are 5mm different between the sedan and wagon and 10mm different between left and right in the rear. You could actually use left hand rear sedan axle for the right hand rear wagon axle. I don't have the FSM for the RS to know if the axle length is the same between the wagon and the 2000-2001 RS. I would imagine they are the same though due to reports that the control arms are the same and since the crossmember (that the control arms mount to) will bolt right up to the GC chassis.

LSD axles are needed for a rear diff that has an LSD. Open diff axles are needed otherwise. Falling into the nether regions of unknown, this doesn't seem to apply 100% when we start talking about early '90's cars.

The outer spline count, located at the hub, for front and rear is the same throughout the years for fronts and rears individually. Your hubs will be fine, it is only the inner spline count that you should be concerned with. I need to finish up my spline count thread in the transmission forum and get it moved over here and made sticky or something.

[EDIT] And just to contradict Jaxx, the Legacy Turbo LSD uses different axles than that of the WRX/RS. I have no idea what the spline counts on those are.

-Jon

Last edited by stimpy; 06-04-2003 at 06:06 PM.
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Old 06-04-2003, 06:48 PM   #4
ciper
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Here is some more confusion.

Some rear axels are a "female" like the front on the inner join and use a pin to connect.
Others are a "male" connection on the inner joint and are held by a wire circlip

Some of the "female" axels have stubs that are basically bolted to the differential while others also use a wire circlip

Your best bet is to take the WRX differential apart and remove the LSD portion. Then try to install it into your original differential using the old ring. Since the axel stubs connect to the LSD you may have to mix and match parts (if its even possible).
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Old 06-05-2003, 12:29 AM   #5
Kha0S
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WARNING:

The WRX rear differential is NOT a 3.90 ratio. It is a 3.545 ratio, due to the 1.1:1 center transfer ratio! The front diff is 3.90, center diff is 1.1:1, and the rear is 3.545:1.

You will annihilate your center diff if you put in a WRX LSD unit.

/Andrew
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Old 06-05-2003, 12:41 AM   #6
serious
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Good thing i'm putting in a wrx transmission and engine too huh?
B
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Old 06-05-2003, 08:14 AM   #7
Kha0S
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Come now, don't give me the :monkey:.

Your original post stated bolting the 3.90 diff right into your 1996 Legacy. A lot of people make the mistake of that differential being a 3.90, and I don't want to see anybody on here munch their center diff just because Subaru picked a screwy center transfer ratio on the US WRX.

/Andrew
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Old 06-05-2003, 03:49 PM   #8
serious
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Yeah, my bad on the center differential/ rear end ration. It is different. What i meant to say was installing a wrx rear differential and not the 3.90.
What's so bad about the munkey? He's not flipping you off or anything.
Brent
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Old 06-05-2003, 03:52 PM   #9
Kha0S
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Depends on the connotation... some people use the disco monkey as a negative comment.

Unfortunately, I don't have spline counts for the rear diff on those vehicles... I had my 4.111 rear diff modified with a 3.9 ring and pinion from an Outback Sport to do my conversion to the Legacy Turbo transmission... so I can't really help.

Good luck with it!

/Andrew
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