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Old 11-05-2017, 11:01 PM   #1
Mrlordcameron
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Question Center diff replacement - questions for the experts pls

Well, add me to the list of people with the circlip / snap ring failure. Drained my trans oil yesterday and metal chunks, lots of pretty sparkles in the oil . Borescope in the drain hole doesn't see any broken gear teeth however.

From searching the forum, it looks like I need to replace the diff with the updated 38913AA102 which uses a c-clip and maybe tack weld that in place.

My questions for those in the know:

1. Is there likely to be damage elsewhere in the transmission eg bearings, due to metal shavings & tiny metal particles in the oil?

2. Is the replacement diff a straight drop-in replacement, or does it need to be fitted eg shimmed?

Transmissions are a black art to me tho am comfortable with most other mechanicals suspension & engine work.

TIA to the forum

2009 Impreza 2.5i, 5MT
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Old 11-05-2017, 11:08 PM   #2
Blktrax
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The center diff fails for 1 of 3 reasons.

1. Mismatched tires or drivetrain components
2. Improperly towed on 2 wheels
3. Abuse

Why did it fail, and that will determine the repair route.
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Old 11-05-2017, 11:35 PM   #3
Mrlordcameron
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Thanks for the response. I am the third owner, bought it last April and unfortunately there was zero maintenance records and very limited info from previous owner.. obviously not a car guy, I was surprised he could even drive stick. Car had matching wheels and tires sizes FWIW.

However, i did participate in a couple of autocrosses in Aug and Sep, there was some enthusiastic cornering and maybe a wee bit of drifting involved... does that constitute "abuse"?

Forgive my ignorance but how does the failure cause relate to the repair route?

I should add that although there were metal chunks which looked like others pics posted that were from the circlip, I don't think the diff has actually failed... yet. Seems to be performing ok on the icy roads we got this week in Calgary Canada, though I am taking it pretty easy on the drivetrain in light of this new discovery.
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Old 11-05-2017, 11:44 PM   #4
Blktrax
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How long is was driven damaged plays a big part.

When the Silicone fluid exits the center diff and mixes with the trans oils , bearings and the Gears are not properly lubricated.

If the damage occurred recently and hasn't been driven on much. Replace the Center diff , drive 300-500 miles change the fuild again, and again after that, to flush out that silicone.

Center diff replacement does require proper shimming clearance.

If it's been that way for a while, or has any odd or loud noises , or bearing scars (contamination) when torn down. Shop for a used trans.
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Old 11-06-2017, 12:31 AM   #5
Mrlordcameron
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Thanks for the info, wish I knew how long ago this started. Would the the silicone stuff in the viscous coupling get released when the circlip was damaged, or could it still be hanging in there, waiting to leak out later on?

I did replace the oil with 75W90, GL5 (not cheap ) so in the (unlikely) best case scenario maybe the timing was such that this just happened and I got rid of the silicone with the oil change. If so maybe I dodged a bullet on other damage but sounds like there's no way to tell until I pull the trans and open it up.

I have no choice but to drive it this week but will order the new diff so it's ready for next weekend. If the damage looks more extensive as you describe, I will then track down a used transmission too, and do the multiple oil flushes... hope not.

Is the shimming a difficult DIY / special tools required? I'll do some searching on the forum but if you can point me to any useful threads that would be very appreciated. I do have the FSM I downloaded from Subaru and maybe it will fill in the blanks, we'll see.

Thanks again for your insights and greatly appreciate your quick responses!
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Old 11-06-2017, 06:55 AM   #6
Blktrax
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Usually the fluid turns a a dark gray/black when the silicone mixes, from the times I've seen it happen in a manual.

Really the only special tool needed is a depth gauge. Subaru wants you to pull the trans , place it bellhousing down to take the measurement. The extension housing gasket replacement is required as it is part of the measurement for clearance. I've done it in the car, but you have to have a lift and 3 arms.

Besides the extension housing gasket, replace the shift rail seal, and output shaft seal.

PM me your email address

Last edited by Blktrax; 11-06-2017 at 07:19 AM.
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Old 11-06-2017, 06:14 PM   #7
Mrlordcameron
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PM sent
Thx again
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Old 11-06-2017, 06:21 PM   #8
Blktrax
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didnt get PM
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Old 11-09-2017, 12:22 PM   #9
Ghoster
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Hey Mrlordcameron -

Unfortunately I've just had the pleasure of working on this exact situation. My center diff was definitely blown and I had started to hear the whine/moan noise from my car as it was being driven. It also had the "clunk" when backing up while turning. I've got 115k miles and was sure I diagnosed the problem correctly. I ordered the diff, the output shaft oil seal and the shift arm oil seal. I located all the torque specs, raised the car on stands and started.
Although I was totally frustrated by several attempts to get the cat portion of the exhaust system out of the way, I finally made it to the transfer case housing. It just wouldn't come off! Although I was tempted, I headed advice and didn't use a pry bar to separate the halves. It took a lot of hammering (several hours of fighting with it) with a block of wood before it came off.
And then I found out why - the snap ring on the diff had failed and there were pieces stuck everywhere. Some of the smaller pieces had taken out several teeth on the input and output shafts. It was a nasty mess. I didn't think there was enough damage to justify replacing the driven shafts. So I cleaned everything and re-lubed the bearings and put it all back together.
Unfortunately, I should have replaced all the bearings while I had the chance. It is still moaning. The good news is the oil looks clean so I'm not grinding off any more bits in the transmission or transfer case. Bad news is I get to take it all apart again and have a local shop press new bearings for me.

For the record, I've been using Amsoil and Royal Purple 75w-90 oil for my changes. The last change (about a year ago) was the first time I'd seen any signs of wear. That's a lot of damange that occurred in a short period of time. I'd personally like to thank Subaru for using a part that could come off in the transfer case and break up into pieces that could be chewed up in the gears. Hopefully, their newer design will not come flying off. Regardless, the car goes back up on jacks today.

For reference, I used The Dutch Garage guy as a reference for most of the work:

Good luck!
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Old 11-10-2017, 12:22 AM   #10
Mrlordcameron
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Yeah, saw that youtube video amongst others. I will be replacing diff & 3 bearings this weekend if parts arrive on Friday. Hoping the shaft gears aren't too messed up by the busted up bits of snap ring. FWIW all the metal bits looked like snap ring not gear teeth, based on the thickness and shape, so have my fingers crossed.

Did you use a gasket, or a sealant eg RTV or similar, when you reinstalled your housing?
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Old 11-10-2017, 10:44 PM   #11
Mrlordcameron
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Never mind, I see in the factory service manual that you use liquid gasket (threebond 1215 or equivalent).

Diff and bearings arrived today. Also decided to get new output shaft seal just for gits and shiggles. Will have to figure out how to extract the old bearings and press the new ones in, that will be fun.
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Old 11-29-2017, 10:00 PM   #12
Greaser007
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2002 Impreza WRX

Default Center Diff issues

Well, guys, I am in a similar dilemma with my '02 WRX Transmission.

My problems began originally 4-years back when I had to put the small diameter spare on the front, and had to limp 20-miles slowly with the transmission / transaxle made a Terrible Klunking sound.

Now, my powertrain ( sounds like transaxle ) begins grumbling after being driven at least 15-miles, so everything gets warmed-up nice.
And the grumble changes pitch with vehicle speed.

So, I removed the Center Diff and ordered the Factory OEM Transfer case output shaft bearings, ( had the Subaru dealer remove the bearing for me next to the helical gear, and I pressed off the small bearing.
Note - the new bearings are different than the originals with More rollers !

End play checked, and dry assembled to make sure of no binding, then lubed everything and re-assembled.

My Center Diff looked good and the bearings on the input and output were smooth and tight.

This did not cure the Grumbling, so I am convinced that the noise is coming from the transaxle assembly, and I have some reason to believe that my pinion bearing is the culprit.

I have not yet pulled the transmission due to scheduling of domestic expectations and responsibilities.

Is there a weak link in the front differential portion of the transaxle assembly which is prone to failure to make the Grumbling noises ?
My transmission shifts normal and smooth.

Now, ......... at the age of 66, and having grown-up with Jeeps my entire life, my experience tells me that when you have Grumbles in the drivetrain, then you have either of tw0 things going-on.
1- Pinion bearings are going south
2- Carrier bearings have gone south

Any thoughts from you guys ?

I have an idea for the perfect Subaru WRX factory package !

I will call it the Subaru WRX-RT ( for Rough Terrain )

It would basically have a scaled-down running gear from your Dodge Power Wagon ! ....... the nice thing about this option is it has a manual locking center differential and both front and rear diffs have electric Lockers.

I have 18-years experience running the Rubicon Trail near Lake Tahoe, California, and believe me you see everything under the sun on that Jeep Trail, and you see lots of equipment failures, and what Works !

Does any of you know if the World Rally Subaru's run Welded Center Diffs

Hope you enjoyed ............

Len
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Old 11-12-2019, 11:08 PM   #13
notamechanic
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Len, how did you end up repairing it? (2 years later, I know). Was it the centre differential or something else?
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Old 11-26-2019, 08:32 PM   #14
Newfieguy9
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I watched the same video as posted above, I have a 4eat with what i suspect to be centre diff issues, is the repair procces going to be generally the same?
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