Subaru WRX Center Diff Bearing Replacement and Viscous Coupling Rebuild

Center differential work done on my newly acquired ‘04 WRX. Bearings were shot in the transmission tail housing and needed replaced. I also rebuilt the viscous coupling, although I am not sure that it needed done. There is scattered info on the web on how to rebuild one, and I by no means claim to be an expert on the matter. So far, the car has driven fine and the rear wheels engage when the front begins to slip, giving me reason to believe my repair is not a failure yet.

[@thesetruths1404]

Hey man thanks. I bought my teen son a 2004 Impreza Outback 5-speed, 156,000 miles. AWD of course. We didn't notice a whine noise, but it just started clicking or tapping around curves and acceleration. I can feel the tapping in the gear shift handle. And it seems it sometimes loses AWD grip when it taps. So I think the center diff is binding the output shafts sometimes. I don't think mine will be rebuildable due to heat. I found new ones with 2 year warranty for $185. Or OEM Subaru ones for $600ish. Any preference or experience? Thanks!

[@stvnswld]

I think that would be fine! I wouldn’t hesitate to use a less expensive alternative, especially on a car with a few more miles. Best of luck with your repair!

[@thesetruths1404]

@stvnswld the reason why I don't think it's the transmission gears themselves is because it makes the noise in all gears while in curves or quickly accelerating. It will do it while coasting in all gears as well, but not as much, and only when not going straight.

[@brianpeterson5332]

This is crazy man.i just got a Subaru outback and was gonna call you about this. It's got a a crazy clunking to it. I'm assuming that this is what's wrong anyway. Don't be too surprised if I get a hold of you today.

[@coko091]

I got my 09 Forester with 110k having symptoms of a bad center diff/ viscous coupler...first started binding on turns after warm up now whines after 20mph...please let us know if that repair was successful and how it’s handling, would like to tackle the repair myself if it’s worth it...checked viscous coupler running around $400-500 new, pricey

[@stvnswld]

Yes, pricey! So far I haven’t had any troubles, but I haven’t driven the car very much since the repair due to other things that need repaired. I figured by trying to rebuild it I was only out the cost of the silicone fluid, plus the cost of fresh transmission oil instead of the viscous coupling unit. I use www.subarupartwholesale.com for Parts that need to be OEM. Best of luck!

[@tannerdruce2186]

Id like to know how long this holds up. Im gonna try the same thing with my wrx i just disassembled my trans for my 03.

[@coko091]

Did you find any other bad parts like front diff bearings or gears? I’m thinking of taking that approach or use borescope to inspect the front diff and just remove the center diff for repair...allot of work to disassemble the whole trans in half

[@tannerdruce2186]

When i took mine apart the input shaft bearing needed replaced too

[@stvnswld]

@@coko091 my gears were fine. The 4 bearings I replaced were all shot though. The snap ring had come off of the viscous coupling so I just figured I would try rebuilding it: not knowing whether it was bad or not.

[@TheCriminal3k]

I need to do this on my car. Did you need to use a puller to replace the 2 bearings in the transfer case???

[@stvnswld]

I used a puller to get the bearings off of the shaft, but the races in the housings I was able to pull out easily with an oring pick. Your case may be different

[@247jeffmarshall]

Hey Steven just wondering if you had the part # for the o-ring that goes on the cap of the center differential coupling?

[@stvnswld]

Sorry, I do not. I did not replace it

[@247jeffmarshall]

@@stvnswld no worries. Also what weight Cs fluid did you use for the clutch disk or what’s recommended? Getting different answers on Google lol

[@stvnswld]

@@247jeffmarshall I used 50 and 100. It still works fine, but I hear heavier is better

[@leonardgriffiths4131]

Great video thanks! Did you use the same shims that came out or did you measure and re-shim with new when re assembling?

[@stvnswld]

Yes, I used the same shims over again.

[@ashleyfigueroa282]

Is there any way you could help me with a part number or way to source the big o ring that keeps everything in the viscous coupling sealed?

[@stvnswld]

Great question. I don’t have any numbers; however, if you take that oring to some kind of implement dealer such as Caterpillar or John Deere, they should have the tools at the parts counter to size one up for you. Perhaps an auto parts store as well. The way they’re measured is a combination of oring thickness and overall diameter.

[@ashleyfigueroa282]

@@stvnswld I will definitely do that! Thank you!

[@procrastinator1842]

Just a few notes on the build of this, I hope you have good luck, but here are a few points that I have learned from building and testing these. The amount of fluid vs air gap is pretty critical. Hopefully you got pretty close. Did you check the gear mesh before and after? There needs to be some clearance. Next time knock out one of the ball bearings in the top plate to relieve pressure. There is a chance the pressure will cause the thrust plate to chew out against the housing. These are finicky little bastards.

[@stvnswld]

Thanks for that info! I did not check the gear mesh, no. Is there info out there on these as far as fluid/air ratio and what to check for? The only real sources I had to go by were a Russian speaking guy and others that simply replaced the complete unit. Thanks again for the comment!

[@procrastinator1842]

@@stvnswld the subaru ones are usually done with weight. 50ml of siloxane @ 0.965g per ml is the correct amount. I use scales to get the correct fill. I think the fill to air percentage is about 87-92%. You could clean it all out and fill it with pure water and work out the volume by mass, but i just replace it with the same amount that the factory used...

[@stvnswld]

@@procrastinator1842 thanks so much!

[@laurentwalmetz7187]

@@stvnswld hello, thank you, you have put the 2 viscosity 50000wt and 100,000 wt

[@laurentwalmetz7187]

@@procrastinator1842 the subaru ones are usually done with weight. 50ml of siloxane @ 0.965g per ml is the correct , hello, in the video weighs 60ml 0.065g?

[@DjOMARi876]

What CST viscosity do you have to use in order to get the 4Kg rating? Is it only 10,000 cSt or a mixture?....

[@stvnswld]

I’m not sure what’s required. I mixed 50,000 and 100,000, so my mixture was 75,000 CST. I went off of several others on KZbin that performed the repair, but information was limited so there was guesswork involved.

[@DjOMARi876]

@@stvnswld thank you very much... and thank you for the video

[@lucid-hopes6217]

how long did it take for your parts too come in?

[@stvnswld]

I believe it was 2-3 days or so. That was before there were shortages of parts.

[@lucid-hopes6217]

@@stvnswld alright cool! I appreciate the response

[@stvnswld]

@@lucid-hopes6217 no problem! Hope your repair is smooth and successful

[@lucid-hopes6217]

@@stvnswld can you tell me how you got the roller bearings off? i managed too get one off, but the other one is far down the shaft (bigger roller bearing)

[@stvnswld]

@@lucid-hopes6217 I used a 2 jaw puller on all of the bearings. They came off alright, but a puller is necessary.

[@PatrickLipsinic]

Where can you get the replacement snap ring?

[@stvnswld]

The Subaru parts page doesn’t show one. I would take it in to a machinery dealership and see if they can get you one similar if yours is non-operational. Perhaps a Caterpillar dealership or John Deere? Any heavy equipment or agricultural dealership should have the resources to find you something. Perhaps even an automotive dealership, I’m not too sure.

[@Mr_BUSINESS_24_7]

Why does the snap ring pop out ? Do you think the snap ring will pop out again ? How did it hold up ?

[@stvnswld]

That is a tremendous question! I’ve got almost 500 miles on since the repair and so far it seems fine. I am not sure how to tell if it pops out again... I didn’t know the snap ring had come out the first time until I took things apart. The real reason for dissemble was the bearings because it was howling and growling so loudly. That noise is DEFINITELY gone, so that part of the repair was effective.

[@Mr_BUSINESS_24_7]

@@stvnswld I'm "thinking" the reason the snap ring pops out is the front diff bearing wears and develops so much play and the rear bearing doesn't develop that same amount of play.. ..so the center diff is able to kinda "cantilever on the rear bearing.. ...which possibly pops the snap ring off ?? That would be my best guess. If thinking the whole reason the center diffs bind, and come apart is because of the front bearing. Another thought I had was that the center diff is taking a beating due to the front tires wearing faster than the rear and people just don't rotate their tires. (I'm guilty of this). Seems you kinda did a pretty good job of "winging it" when you rebuilt it. Meaning... ....yes, you rebuilt it, no doubt. I'm wondering if there is a tutorial out there with more absolute information. Your tutorial is HUGE progress.. ... would love to learn more. I replaced the center diff in my old 5mt with a donor center diff. But then that transmission ended up with internal issues, popping out of gear. And I know how expensive parts are for these transmissions. So I couldn't justify rebuilding that transmission. So I went to the boneyard and bought another transmission. Now this center diff is binding a couple years later. And if course I scrapped my other transmission and didn't tank the low mileage center diff out of it. :/

[@stvnswld]

@@Mr_BUSINESS_24_7 you are totally right, I winged it. I figured if the rebuild of the viscous coupling didn’t work I would buy a replacement, but at $500 or whatever it is, I thought it worth the try. Honestly I don’t know how slim the margin for error is in this particular case. Your explanation for failure makes sense. Thank you for the feedback, by the way!

[@Mr_BUSINESS_24_7]

@@stvnswld All good ?? Did you find success ? Where does the 100k CST go vs. the 50k CST ?

[@stvnswld]

@@Mr_BUSINESS_24_7 I actually sold the car to a friend who lives in Wisconsin. He drives the car a lot, and it recently started howling again. He replaced the bearings AGAIN and found the viscous to be intact with the snap ring still in place, so that part was a win. Not sure why the bearings would have failed though, especially so prematurely. What was your question about the cst?

[@procrastinator1842]

Hello. Great video, I'm currently on a similar mission. I have the same centre diff and it has been rebuilt to 12kgf/100rpm (stock is 4kgf/100rpm. It has transformed my Subaru but now my rear differential is the weak link. The next time I will rebuild the centre diff myself. I have done some testing on a lathe with a viscous rear lsd and found that it is also approx 4kgf/100rpm, and have purchased siloxane to see if I can build a high performance lsd. In my rear differential the construction is nearly identical, 13 inner plates, 14 outer plates, 13 rings and a thrust washer. Could you please give me a rough diameter of the outer plates? I'm sure they are identical to the rear differential ones... Thanks!

[@stvnswld]

Thanks for the comment! Good question, I didn’t measure the plates once I had them out. I would estimate roughly 4 inches? Sorry I can’t get more specific.

[@procrastinator1842]

@@billycorgi6342 Billy, I'm pretty disappointed that you don't show any customer confidentiality. This is twice now you have done this to me. The first time, I purchased two diffs, one for a rally car, and although mechanically identical to the original, we decided not to use it as it was a modified part and was possibly outside of the class rules. It's still in a box, unused. You then decided to divulge my details and purchases to another MSCT member, who informed the club scrutineer, who now believes we are 'cheating'. So please, in future, respect your customers privacy.

[@andydos9314]

@@stvnswld ​ please, what is that CST fluid exactly? Cant find that on google or in store, is there some proffesional name for that, is it possible to build that Differential without it?

[@stvnswld]

@@andydos9314 www.ebay.com/itm/183507459103?mkcid=16&mkevt=1&mkrid=711-127632-2357-0&ssspo=nWjvc8TBSMe&sssrc=2349624&ssuid=ccjrpNmcTVq&var=&widget_ver=artemis&media=COPY

[@MotoBlackbird]

@procrastinator1842 Hey. Can You say, what fluid CST should be used 10-12kgf?? 150000cst, 200000cst ????

[@rittermiklos8276]

Hi!Can say someone, whats the name of the used oil (on the transparent tube).Thanks!

[@Billybong12088]

After watching your video I think I'm going to a temp this myself. I was wondering do you know the part number for the snap ring for the top and do you have to do a layer of silicone between each disk or every set? Great video by the way

[@stvnswld]

I don’t have a part number for the snap ring, no. I think the new viscous coupling has an updated snap ring that stays in better, so that’s one downside to rebuilding and reusing the old one. I was tempted to use an adhesive to lock the snap ring back in place, but I didn’t end up doing that. I layered the silicone between disks, just to make sure everything was coated good. If you read some other comments, they recommended removing the balls from the cover/plate to allow excess air to escape. I didn’t do that either. Thanks for the comment!

[@scottpilgrim69]

So if I have a 02 wrx wagon, same part #s?

[@villedocvalle]

Great work!

[@bullnukeoldman3794]

Steven - I just watched this because my center diff is likely failing and am wondering how long/if your rebuild lasted. I find it interesting how simple the component really is and if rebuilding with cleaning/new fluid/resealing is an effective process. Because of the simplicity of the component I wonder why Subaru considers it a non-repairable piece. It almost appears to be a cash grab to require replacement of a $500 component. By the way, I saw the Russian guy's video also and he was pretty good. I really need to learn that language. LOL! Thanks, man, for the great video.

[@stvnswld]

Thanks for the comment bro! I actually sold the car to buy a Baja, so I don’t have it anymore! However, the guy who bought it and I became friends and communicate fairly regularly. He’s having no issues with the diff, so I’m calling it a win for the money saved. Whether it was by the book 100% or not, it’s holding. It’s not a race car either, so it doesn’t need to withstand the most extreme conditions.

[@bullnukeoldman3794]

@@stvnswld I rather wonder why no one has a cottage industry of some sort to open, clean, refill, and reseal these couplings with new fluid (assuming no gear/internal bearing damage) as an additional option to buying a $450 to $500 new center diff. If nothing is truly broken or damaged beyond bad fill silicon fluid then why not? I believe that I'll give it a try soon. If nothing else and my attempt fails I'll already have all the fasteners broken loose to replace it again. LOL!

[@stvnswld]

@@bullnukeoldman3794 you’re exactly right, I figured it was worth saving the money to give it a shot!

[@RayHogarth]

Why don't Subaru use a water Mellon it would give a better 50-50 torque than the six jam tarts that is used.

[@stephenhunt6253]

That's impressive! Subaru thinks these things aren't servicable. You clearly proved that wrong.

[@06wrxRAR]

how much does this cost to replace and rebuild these things? just curious what a ballpark figure should be

[@stvnswld]

My guess now is a few hundred. Should be less than $500.

[@20VA]

are there 4 bearings in every wrx ??? ... I have a 2020 Limited and my viscous coupler appears to be FUCKED ... sounds like the driveline is playing mutha fuckin JUMP ROPE double dutch addition up under the car whenever I turn at low speeds ( like pulling into a parking lot / spot ) ... this only occurs after driving for 2 and a half years however ... through EXTENSIVE research I have learned that viscous coupler is the issue because I KNEW it wasn't the drive shaft or axles or tie rods or struts or anything to do with the steering or suspension itself ... but I figure if I have to disect this bitch ... might as well replace ALL the bearings just to be on the safe side if I need to replace the viscous coupler

[@stvnswld]

Dude your comment cracked me upso much. Jump rope double Dutch! 😂 I honestly don’t know how they changed the wrx center diff through the ages. This video was on an ‘04 model. Here’s a link to the parts page for the 2020 model. www.subarupartwholesale.com/a/Subaru_2020_WRX-20L-6MT-Limited/_80160_6464378/MT--TRANSFER--EXTENSION/V10-121-03.html

[@20VA]

@@stvnswld ... lol ... that's my swag G ... I have to make everything funny

[@Turbo20l]

Hi Steven, thanks for posting your video. My WRX has a whining noise coming from front or center of the car. I've had the wheel bearings checked and they're good. I also have brand new tires. I'm thinking it might be the 6spd transmission or center diff. Did your noise sound something like this? kzbin.info/www/bejne/bHXZh3murs-WaJo&ab_channel=Turbo20l The noise starts to get noticeable around 30-40mph, and really loud above 70mph.

[@stvnswld]

More than likely, yes! Mine got louder as I sped up, but I could still hear it as I idled down. It definitely was coming from the center by the gear shift though.

[@stvnswld]

Here is a video of what I experienced: kzbin.info/www/bejne/fpmzkouCnKhnsNk

[@sanders2strong]

replace that viscous with a torsen xD

[@herrtomkat92]

I’ve discovered that it’s easier to simply replace the transmission, costs about the same, for a base model rs at least, not sure about wrx. Good video otherwise

[@orion7741]

LOL.... what fantasy land are you living in??? there is no way at all that you could replace the transmission for the same price. you must be high. jeez, even out of a junkyard, you wont find a transmission for less than $500. and those are totally untested and you have no idea about what condition everything is in. For a reliable transmission, you are looking at $1,000 at the very minimum. Doing this repair like in the video will only cost about $200-300. and that is only if you replace all the bearings and seals. I have done this exact same repair a couple times now and I have only spent $75 on each job, that includes everything you would need for the job.