Center diff. shimmng

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chrisshara
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Joined: Thu Apr 26, 2012 1:41 pm
Location: Middletown, CT

Center diff. shimmng

Post by chrisshara »

Team,

My center diff started seriously whining on deceleration on my '04 Outback. (I assume the set up and shim measurement procedure will be the same or similar between an '04 Outback 5MT and a First Gen. with 5MT) I found the service bulletin that discusses updating the tailshaft extension case (center diff end cover) on the '99 up Legacy, Outback, Forrester. and that bulletin provides the specific information and all details for the measurement process and equations for choosing appropriate shim sizes in the center diff case. BUT, I am not convinced that I want to drop $220 on this extension case Part #: 32130AA360 and (9) case bolts of a shorter length. This updated case adopted a dish plate to compensate for the shrinking of the center diff case in colder temps that allowed for too much tension on the tapered roller bearings on the driven gear shaft inside the center diff. and thus caused premature bearing failure and un-necessisary whine from the gears, leading to chipped or even completely broken teeth on the center diff drive and driven gears. In my situation, I only have a few chipped teeth on the driven gear. I will be trying to reuse it and see how it sounds.

I am just unsure if it's really worth it to actually go as far as updating the extension housing. Or just slap it back together with the old cover and get probably another 100k out of it before having to replace the bearings again. I feel like, I'd like to slap it back together. But, since I replaced the bearings and will be replacing the center diff, as well, (becuase mine fell apart and the bearing on the center diff was toast), I feel like I should be taking measurements due to replacing the center diff. and all (4) bearings. So to recap:

1) Is it worth it to update the center diff extension housing part # 32130AA360 ??

2) If it's not worth it to update to the newer extension housing, Does anyone know the measurement proccess for selecting shim sizes inside the center diff on '99 up Legacy, Forrester, Outback? Or do I have to join another forum ? Lol .....Thanks everyone ! !

P.S. Does anyone know the differences between the drive and driven gears in the center diff between the '02 WRX and my '04 Outback ? The extension housing, center diff, and the complete transfer casing is all the same between the '02 WRX and the '04 Outback. The reason I ask,is becuase I can get the drive and driven gears from an '02 WRX for a very good price. I'm wondering if they will fit. But I am not seeing a reason wy they would not fit, sincce the center diff and both the transfer case housing and extension housing are all the same.
94 Legacy GT
95 BMW (E36) 325ic
81 BMW (E12) 528i
04 Outback
02 Acura TL Type S
Alphius
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Re: Center diff. shimmng

Post by Alphius »

The drive and driven gears on the WRX center diff incorporate a 1.1:1 ratio, the WRX front diff is a 3.90 and the rear diff is a 3.54. The center diff gearing of 1.1:1 makes the rear diff match the front ratio.

If you ran a 1.1:1 center diff ratio with a 4.11 front diff like the Outback has, you'd need a 3.74 rear diff which doesn't exist.
chrisshara
First Gear
Posts: 164
Joined: Thu Apr 26, 2012 1:41 pm
Location: Middletown, CT

Re: Center diff. shimmng

Post by chrisshara »

Alphius,

Thank you. Yes, that makes perfect sense to me. I just did't know the front and rear diff ratios were not the same on the WRX. Again, thank you.
94 Legacy GT
95 BMW (E36) 325ic
81 BMW (E12) 528i
04 Outback
02 Acura TL Type S
Legacy777
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Re: Center diff. shimmng

Post by Legacy777 »

It seems like you might be able to get a used transmission for almost the cost of doing the extension case. Unfortunately I don't have much else to add.
Josh

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1990 Legacy (AWD, 6MT, & EJ22T Swap)
2020 Outback Limted XT

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chrisshara
First Gear
Posts: 164
Joined: Thu Apr 26, 2012 1:41 pm
Location: Middletown, CT

Re: Center diff. shimmng

Post by chrisshara »

I got the center diff, drive and driven gears for.. ...FREE... ...front a '10 Impreza with less than 100k on it.
94 Legacy GT
95 BMW (E36) 325ic
81 BMW (E12) 528i
04 Outback
02 Acura TL Type S
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