Subaru center differential rebuild (viscous coupler)

2 fluid oz of 200,000 cst silicon fluid (59ml 200k cst)
Available from Amazon/eBay/RC car hobby shops.
Full rebuild video. Driving with this rebuilt part daily. Works better than before! This is also a follow up to a previous rebuild video where 45ml 100k fluid was used. It began to wear down after 50,707 miles. Deleting old videos so that this better video is found.
Symptoms: binding/pulses of resistance/thuds during turns at low speed only. And only when transmission is hot. Symptoms do not present themselves with a cold/cool transmission.
I am not a mechanic. Translate and repair at your own risk

[@cloudwalker3650]

Thank you for what I believe is the MOST THOROUGH, TECHNICAL center differential/viscous coupling repair video available as of December 2023!!!! This will help A LOT!! 👍

[@ovalwingnut]

Damn. Good job and outstanding post production efforts. Cheers from Long Beach, CA

[@orion7741]

hey, thanks for the updated video on this. I really appreciated your first 3 videos that you made, and also the additional updated info that you put in this one. I do have some criticism for you though. You seem very "rushed" and impatient in the video and you tend to skip forward in the video. I understand that you might not feel the need to show every thing because you have done this procedure a couple times now, but one thing to keep in mind is that there are people watching that have not, and might not even be close to having the knowledge and experience that you do. Leaving the original footage as complete as possible would be very helpful to people watching. Take your time, If that means splitting up the full video into multiple parts, then do that instead of kind of rushing through everything. Personally I think your original 3 videos were much much better than this updated one because they covered quite a lot more of the process and did not skip over steps like you do in this video. I would encourage you to redo the video again, and maybe put together a loose script for yourself to follow so that you dont sound kind of "lost" and frantic at times. It would also be very valuable for people if you did a video (series?) covering the job from the very start to the finish, I mean the entire job from the very beginning (jacking up the car, drive shaft removal, transfer case removal), all the way to the very end (putting everything back together and cleaning up). yeah I know, it would be a ton of work, but it would be worth it. it would be super helpful to people and would be something that you would never have to come back and redo or think about it again. anyways, thank you for your efforts with the videos. This video is nice as an update, but feels unfinished and imcomplete when compared to your original videos, I personally think those were more detailed and did a much better job at explaining what you were doing and why you were doing it.

[@jonmark2688]

Hello. Thanks for the tips. I did this in one take, the first take and skipped nothing except repetition. If this fails again within 50,000 miles again I might produce a rebuild based off your ideas.

[@ali-zc2it]

thanks this makes me feel confident enough to do it myself. very helpful bro

[@gorandanilovic5827]

Informative video thanks paaal! You just saved me $650

[@stvnswld]

Great video! I have a video of rebuilding a WRX center diff, but it is a bit more crude than yours. I don’t have the car anymore but I know the next guy has had pretty good fortune with it. I used a combo of 50 and 100k cst, but it looks like I should have beefed that up a bit. Nice work!

[@dukeofnyd1]

I appreciate the info! I have 2 100k cst bottles to rehome now 🤣🤣🤣

[@nick_sta]

Hi mate i'm just about to have a go doing this. Thanks for the video. As you started on an 'Outer' plate and ended on an 'Outer' Plate, this would suggest 25 plates and 12 wires, not 24 plates as said. 13 Outer plates, 12 inner plates and 12 wires.

[@miketaylor7487]

On that top plate you removed the plug for the hole or ball bearing. Then you staked in the plug. Great video!

[@TheWizechatmgr]

Next time try putting it in a vac. chamber overnight before you try putting the top on - you likely have tons of air bubbles between the plates, etc. This will make it a real b**ch to close.

[@chriskucia8348]

Interesting video. Thanks for putting it together. So it looks like there aren't any seals keeping that fluid inside the plate chamber? I guess the fluid is thick enough that it can't get out through the gaps? Also curious what keeps oil from getting in although maybe having it filled with fluid keeps the oil out. Pretty fascinating.

[@MaurizioSelatti]

hello and thanks for the video really useful ...so what seems to be the right oil or closer to OEM? the 100k or the 200k ? And what does it change between the two when used?

[@marcelocuadrado6955]

Good video, can you tell me the specifications or what type of high density fluid you use to lubricate the inside of the core?

[@NPF_TV]

What year is this out of? Sti? Wrx? Great video!

[@thesetruths1404]

When you initially rebuit the coupling did you replace hardware or only clean and lube it? Mine started clicking about 100 miles ago. My manual transmission oil was 1.75 qt low, so i refilled it but the clicking still clicks.

[@thesetruths1404]

What probably happens if the center diff is clicking and bad, but it's still driven? Does it stop putting power to the rear wheels eventually? Or the front wheels?

[@user-vp3ub9mo4v]

Greetings! Tell me, how does a viscous coupling behave with 200 thousand oil?

[@grantmacdonald4838]

Did you have any bearing noise when you did the initial rebuild? I have a transmission which is giving quite a bit of noise and is just now starting to show binding.

[@gabigabriel9738]

Hey. Excellent video. I also did this operation a few years ago but I think I made a mistake somewhere... it worked well for me for about 25,000 miles then it failed. The liquid I used was 50,000 cst. I think I made a mistake at arranging the discs. My question is if 200000cst is not too thick and will not heat up faster than 50000cst?

[@jonmark2688]

It seems to me, combined with your stats, that the 200k reduces the number of rotations. With the 50 or 100k the front half of the drivetrain 'drags' the rear half, engaging before the brakes and engine. So every start and stop engages this coupler, whereas the 200k allows the brakes and engine to not cause this excess rotation of the coupler... i.e. less heat, not more

[@vihreelinja4743]

Sure it will slip less with thicker liquid. Good video but i would put the sealant in to the groove before putting the lock ring back. Thought i need to buy a new one when this fails but seems simple enough to just change the silicone.@@jonmark2688

[@timtiminy]

What would you say the 200000cst fluid puts the locking force of the coupler at? I heard stock 4kg is 100000cst fluid. I would think 200000cst being 2x would yield 8kg?

[@thesetruths1404]

Hey there i have a 5-speed manual 2004 Impreza Outback N/A that i bought for my son as a first car. Test drove it for 500 miles and it seemed fine. Tagged it for legal driving and 200 miles later i have some kind of binding click noise that happens randomly, but more often when the tires are operating on muddy snow terrain. I can feel the clicking in the stick shift handle. The tranny gear oil was about 1.75 qts low. I filled it and sound is a little less present but still present. Is the center differential lubed by the same gear oil reservoir as the manual transmission? What do you suggest to do? Thanks!

[@jonmark2688]

Yes the center differential is lubricated by the gear oil. Even though the manual calls for 75-90 every version of that grade contains LSA (limited slip additive) which the Subaru manual transmission cannot operate with because it is a combination of a transmission and a differential, known as a transaxle. If you have been using 7590 gear oil with LSA added, I would drain out all the fluid and instead use 80 90 gear oil. In the united states, 8090 does not have the LSA which can cause problems in your Subaru transaxle. If that doesn't resolve your problem, then you'll have to open the transmission to see what's going on inside

[@thesetruths1404]

@jonmark2688 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. I will refill with 75-140 when I flush it.

[@lucullustechnic9271]

Can you elaborate what you meant with "delay" when describing the symptoms after the first rebuild? In which road conditions did this occur? I am asking this because it somehow makes no sense in regard to the mechanical working principle of this center differential. Under normal driving conditions (high traction, no wheel slip) the viscous LSD doesn't play any role in transmitting torque to the wheels. It is all done by the mechanical parts of the differential (the bevel gears). In this state there should not be any delay even if there was no fluid at all in the viscous unit. It would still be permanent 4 wheel drive, only without any limited slip capability. If the weight of the fluid is too low, this should only be noticable when there are big traction differences between front and rear wheels (ice patches under one axle). This would cause speed differences between the inner and outer disks in the viscous unit and by that, the shearing forces in the fluid would start to force the non rotating parts to rotate which would result in torque transmitting to the slower axle. Another thing to keep in mind is that there should actually be a certain amount of air in the viscous unit to allow the silicone fluid to expand when it gets hot. This is also mentioned in Subarus technical reference manual: "The viscous coupling consists of a number of alternately arranged inner and outer plates and air and- silicone oil mixture filled into a sealed space that is formed by the center differential case and the rear side gear of the differential gear set. The inner plates have their inner perimeters splined to the side gear and the outer plates have their outer perimeters splined to the center differential case. The outer plates are held apart by spacer rings. There are no spacer rings between the inner rings, so the inner rings are movable slightly in axial directions. X-section rings are used to prevent leakage of silicone oil, which would otherwise occur if the oil is pressurized due to large difference in front and rear axle speeds."

[@jonmark2688]

Delay... at a red light turning green, I would press the gas and move forward, but then there would be a fluid like 'thud' which I presume was the rear half engaging via the coupler. The same diff rebuilt in this very video is running flawlessly about 9k since

[@dougthueneman]

2017 forester 6spd manual failing at 52k miles....

[@rubenbojorquez4614]

hey great video @jonmark2688, how did it work with 200,000 CST? I am about to do the whole thing.

[@jonmark2688]

still working amazing. at least 6k since the change. I drive a lot

[@NickSchuetze]

@jonmark2688 @rubenbojorquez4614 I'm going to be installing a 300k CST fluid sample in my center diff in the next few months. I'll post my experience once I have it.