Subaru R180 CLSD rebuild | The Z Club of Great Britain
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Subaru R180 CLSD rebuild

Discussion in 'Drivetrain' started by 240L31, Dec 3, 2020.

  1. 240L31

    Z Club Member

    Hey guys,

    I just bought a set of new friction plates for my Subaru R180 3.9 LSD (Black Friday sale). My diff features a lot of backlash (around 0.19 which is exactly at the upper spec), therefore I wanted to open it up anyways. While I am at it it's not too much work to replace the clutch plates. Just for the peace of mind.

    Is here someone who ever
    A) changed friction plates
    B) modified ring/pinion backlash?

    I am looking for advice, maybe there's something I haven't researched yet. I.e. some talk about factory recommendations regarding the total friction plate stack height, I couldn't find this anywhere. The OE manual basically says "opening of the diff carrier is not allowed" (just replace the unit).

    Last edited by a moderator: Dec 14, 2020
  2. Albrecht

    Albrecht Well-Known Forum User

    Setting up a clutch LSD assembly is quite complicated if you are aiming for a particular breakaway figure. You would need to make a fixture that allows you to hold the complete assembly steady whilst you turn one output against the other, and 'measure' the breakaway torque figure.

    There are usually formulas for the friction plate and spacer stack combinations which put you in the ballpark for certain breakaway figures. I have followed them for the OEM Nissan and NISMO CLSDs which I have taken apart and rebuilt (R180, R192 and R200) and there will - for sure - be similar data for the Subaru-specific Fuji Heavy Industries diffs, so I'd seek them out if I were you.

    You won't want to go for too high a breakaway on a regularly street driven car.

    Rebuilding the rest of an R180 and getting the ring & pinion settings back to factory specs is another matter altogether. Setting the pinion height in particular is really hard work, requiring all sorts of special tools and the purchase of the correct shims and new crush collar. It is much harder than on the R200, and - honestly - I would rather give it to a diff specialist than do another one myself.
  3. 240L31

    Z Club Member

    I agree with all your points, especially that it might be wise to consult a professional rebuild shop. However, I really like to learn new things like a diff refresh. I've been disappointed many times by "professionals", so I lost quite a bit of trust.
    My plan so far is to exchange the OE friction disks + plates 1:1 for the racingdiffs plates. I won't touch the pinion height but will try to reduce backlash by moving the ring gear towards the pinion.
    No, I didn't find anything like this. The OE manual only describes how to swap the complete diff unit, not the individual clutch plates.

    Re crush collar: There is none in the Subaru R180, only a height adjustment shim which is only dependend on the diff case+pinion.
    Last edited: Dec 4, 2020
  4. Albrecht

    Albrecht Well-Known Forum User

    I'll have a look around myself to see if I can come up with anything that might be useful reference.
    jonbills and 240L31 like this.
  5. Fosworth

    Z Club Member

    Very sound advice.
    Before I retired I was a self employed transmission engineer and quite a bit of my work was trying to repair the work of well meaning enthusiasts. Without the correct tools and knowledge it is a minefield. Once you have done it a few dozen times it seems quite simple but it is getting there that is a very frustrating and very expensive journey. An important point is that no matter how many books/manuals you read you will end up in deep water. Sorry to sound negative but my only intention is to try and stop anyone backing themselves into a corner. Finally, yes LSD's are a seperate issue altogether.
    atomman likes this.
  6. 240L31

    Z Club Member

    So, finally an update. I worked myself quite deeply into the topic of diff rebuilds and how LSDs work. I agree that changing the backlash is not a good idea for everyone, however: Rebuilding the clutch pack is doable and actually not really difficult. No special tools required.

    I did the refresh this winter and returned the diff back to factory spec. For those that are interested I did some renderings and explanations:

    1. The Subaru R180 consists of 2x 5 friction disks/plates + beleville washer.

    2. From factory, some of them have "inactive" sides, so they never wear a bit (as they can't move). This is super nice for a mild rebuild as you can flip an rearrange the plates in a smart way, having new friction surfaces after. This is what influences the "locking" factor. The second parameter, LSD preload, is adjusted by the internal clearance of the housing (NISMO spec: housing height - stack height = clearance 0.06-0.24mm)

    Stock disk arrangement:

    (1) Beleville washer (preloads the stack)
    (2) added by me, more on this shim later
    (3) Friction plate: Note the green line above and under (3). What I mean by this: Both top and bottom are never being used, so essentially brand new
    (4) Friction plate - top new
    (5) Friction disk
    (6) Friction plate
    (7) Friction disk - bottom new


    What I did: exchange (3) by (6), flip (4) upside down, exchange (7) by (5). Voila, 4 brand new friction surfaces!

    Next thing that needs to be adressed is the wear of the clutch plates. As they wear down, internal housing clearance increases and preload decreases. That is why I had a shim laser cut ((2) in above diagram) and placed under the beleville washer.

    I did quite sophisticated measurements to figure out the internal clearance (depth micrometer and micrometer). I shimmed it down to a final clearance of 0.12mm.
    I'd say this type of measuremt isn't really required as the LSD pack is set up extremely loose from factory.


    I highly recommend this sort of refresh as it is cheap (compared to a 400€+ rebuild kit) and fun. Backlash etc. isn't changed at all, so you don't have to worry about messing something up.

    If someone needs a spacer shim too send me a PM (I can do some more).
    Last edited: Feb 5, 2021
    Huw, Woody928, mick280 and 6 others like this.
  7. jonbills

    ZClub Administrator

  8. Woody928

    Z Club Member
    Staff Member Moderator

    I bow down to your knowledge and some other very smart people on here, this is truly awesome work!

    I've got exactly the same diff and its certainly showing signs of wear these days with the use and abuse its been given. I'd love to get my head around it however I'm having enough of a time doing that with the engine right now. Perhaps one for the pro's in the future....
  9. Dave J

    Dave J
    Z Club Member

    You can ring me if you wish, I rebuild them, Matt (Racer) will give you my number.
    Woody928 likes this.
  10. Woody928

    Z Club Member
    Staff Member Moderator

    Well that's good to know, I'll keep it in mind and get your contact details when the time comes in that case. An engine and gearbox to sort in the meantime!

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