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2001, 2.5RS, dark blue
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16 Posts
Discussion Starter #1 (Edited)
So I just picked up a 1997 Impreza outback with an automatic transmission. It needs some work and I’m trying to breath some new life into it. The rear diff is making a lot of noise and I’m looking for a used one but not having much luck. I’ve been finding conflicting information about differentials that are compatible. I’ve read the final drive for this car is 3.9 on some forums and 4.11 in others so I was hoping someone could chime in on what I should be looking for. I’m sorry in advance if this has been covered somewhere obvious. I know someone will tell me to use the search function and I have I just can’t find a concrete answer. I don’t want to buy the wrong thing.
 

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2006, 2.5i Black Wagon
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15 Posts
I believe the differences in the final drive are from if its a manual or automatic.
Manuals I think have the 3.9 and Autos have the 4.11.

Could be wrong though...
 

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2001, 2.5RS, dark blue
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16 Posts
Discussion Starter #3
Yeah that’s what more sources have said. So I went ahead and ordered a 4.11 rear diff. Should have it by Thursday. I’ll confirm on here that it works.
 

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2001 2.5 RS Sedan
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4 Posts
Yeah that’s what more sources have said. So I went ahead and ordered a 4.11 rear diff. Should have it by Thursday. I’ll confirm on here that it works.
Worst case you can just swap the ring gear from your current diff onto the new one, that'll keep your gear ratio the same.
 

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2001, 2.5RS, dark blue
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16 Posts
Discussion Starter #5
Worst case you can just swap the ring gear from your current diff onto the new one, that'll keep your gear ratio the same.[/QUOTE]
I hear you but the ring and pinion are destroyed. The diff had a leak and the last owner drove it till everything completely let go.
 

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2001, 2.5RS, dark blue
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16 Posts
Discussion Starter #6
I got a new diff. It’s a 4.11 out of an 09 legacy. It’s really rusty so I’m trying to find a blasting service to clean it up before I install. It would be the only rusty thing on the car. But once I install it I’ll confirm it works with the 2.2 auto Imprezas
 

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2001, 2.5RS, dark blue
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16 Posts
Discussion Starter #7
Wrong final drive... pretty pissed off. The trans and rear diff are fighting and Is completely undrivable. I guess it’s 3.9 but I really want a solid sourced answer. Can anyone help with this?
 

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2001 SRP 2.5RS/RA/SOHC Monster
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2,795 Posts
No one can give you a solid answer without knowing the trans code.
 

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1995 EZ30 Coupe
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550 Posts
Jack the car up and put it in drive. You've got a 4.111 rear diff, correct? If the rear wheels spin faster than the fronts, your trans is a 4.444 FD. If the rear wheels spin slower, the trans should be a 3.90 FD. The higher the final drive, the slower the wheels will spin at a given engine speed, so you should be able to figure out which direction to go. Good luck!
 

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2001, 2.5RS, dark blue
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16 Posts
Discussion Starter #11
Jack the car up and put it in drive. You've got a 4.111 rear diff, correct? If the rear wheels spin faster than the fronts, your trans is a 4.444 FD. If the rear wheels spin slower, the trans should be a 3.90 FD. The higher the final drive, the slower the wheels will spin at a given engine speed, so you should be able to figure out which direction to go. Good luck!
I’ll try that tonight but I guess I could have been sold the wrong diff off eBay. The seller told me it was a 4.11 out of a 09 Legacy 2.5 no turbo and that it would definitely work with my car.
 

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1995 EZ30 Coupe
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I’ll try that tonight but I guess I could have been sold the wrong diff off eBay. The seller told me it was a 4.11 out of a 09 Legacy 2.5 no turbo and that it would definitely work with my car.
Hmm that could be, and would be very unfortunate. I wouldn't know with anything as new as 09, but back in the 90's and early 00's the base models/L's typically had more economical gears like 3.90's vs the GT's and RS's which had sportier gears like 4.11's. Those are the numbers for the manuals though, autos could be different.

I think you can spin the driveshaft manually and count how many times the rear wheel spins for the ratio? I read something along those lines long ago, might help you determine the rear diff at least.

Edit: oh yeah, have you ruled out torque bind in the trans itself?
 

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2001, 2.5RS, dark blue
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Discussion Starter #13
I’ll try that tonight but I guess I could have been sold the wrong diff off eBay. The seller told me it was a 4.11 out of a 09 Legacy 2.5 no turbo and that it would definitely work with my car.
Hmm that could be, and would be very unfortunate. I wouldn't know with anything as new as 09, but back in the 90's and early 00's the base models/L's typically had more economical gears like 3.90's vs the GT's and RS's which had sportier gears like 4.11's. Those are the numbers for the manuals though, autos could be different.

I think you can spin the driveshaft manually and count how many times the rear wheel spins for the ratio? I read something along those lines long ago, might help you determine the rear diff at least.

Edit: oh yeah, have you ruled out torque bind in the trans itself?
Well I was thinking about that and wondering if my center diff could be damaged from the rear diff blowing up but my experience with center diffs binding only happens when turning. My car is binding going straight too, even just slowly creeping forward or backward
 

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2001, 2.5RS, dark blue
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16 Posts
Discussion Starter #15
Alright so I think this is the right diff. I think the problem I’m having now is the solenoid that controls the awd system. I’ve been using my jumpbox so every time I disconnect it all the memory disappears. I left the jump box on and started the car again and I got the flashing AT temp light. 16 flashes which I remember being a stored DTC in the TCM. I don’t have a way to scan the TCM on this car but I tried putting it in fwd mode with a fuse and it didn’t work which from what I can remember means a short in the transfer clutch solenoid. So I’ll be pulling the tail shaft off this weekend to see what things looks like. I’m just hoping whoever had this car before me didn’t drive it like this too long because there could be some more damage.
 
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