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Old 05-30-2015, 05:16 AM   #1
mrsaturn7085
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Default Rebuilding the R180

Due to a failing side bearing, I decided to rebuild my R180 rear diff. on my 2006 STI. Not wanting to make the effort for only OEM performance, I snagged an STI rebuild kit and a set of STI 60 deg diff ramps (one of the last sets - these are now discontinued).



I'm not going to go into the whole walkthrough, as there are plenty of pictorial guides out there, such as:

R160 - http://www.scoobymods.com/showthread...14270.html?amp

and

R180 - www4.pf-x.net/~specc/work/work-specc/work_page6/work_page6.html

Disassembled:



Swapping gears to new 60 deg pinion:




Old 45 deg ramp:



Old plate stack:



Figuring out plate sizing:






In the bottom-right quarter of the above image, 86.64 mm is the internal case depth, measured as instructed. Subtract 65.99 mm (the assembled pinion/ramp thickness) to get 20.65 mm left for spring plates (2), friction disks (4), and friction plates (6). New spring plates are one size - 1.85mm (much thicker than OEM), and new friction disks are 1.70mm (same as OEM), leaving me with 10.15 mm to fit 6 friction plates with 0.06-0.24 mm remaining.

Friction disks come in 3 sizes - 1.60, 1.70, and 1.80 mm. All sizes were accurate within 0.01 mm. The only combination that fulfills the requirement is two 1.60 mm plates and four 1.70 mm plates. As I noticed when I disassembled the OEM assembly, thicker plates were placed on the outside.

One thing that the 60 deg diff ramp kit modifies in the instructions (not shown) is the order of plates and disks. The OEM and rebuilt kit order places a friction disk directly against a ramp and has two friction plates against each other. This causes the diff ramp to wear, and you likely achieve a marginally lower initial torque as you are basically getting 3.5 points of frictional contact rather than the full 4 (per side).

The new order used is as follows:

Spring Plate | 1.70 Plate | Disc | 1.70 Plate | Disc | 1.60 Plate | Center | 1.60 Plate | Disc | 1.70 Plate | Disc | 1.70 Plate | Spring Plate

Don't lose the thrust washers (re-use them) and don't forget to lubricate ALL plates and discs with 90wt oil!
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Last edited by mrsaturn7085; 07-06-2017 at 07:32 PM.
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Old 05-30-2015, 05:17 AM   #2
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Sealing the assembly up:



Don't forget the match marks!



Bolts secured with Loctite 243 in accordance with the FSM. (Three-Bond Red = Loctite Blue!)

Double-check to ensure you didn't lose the axle retention clips:



Bearings were replaced by a local shop... good luck if you try this at home! The races are EASY... but the bearings themselves are a nightmare.

Re-shimmed each diff carrier side plate with new shims but retained the sizing that it had initially. Checked my preload with a trigger-pull gauge (not perfect but it works, and preload was right in the sweet spot in the middle of the range).

Checking tooth contact:




Not "perfect" but well within the acceptable range (see the first example pattern image in https://www.ringpinion.com/Content/B...h-Patterns.pdf)

Everything from this point is straightforward according to the FSM, with the addition of some LSD burnishing to be completed by doing ~30 minutes of figure 8's followed by a diff oil change (yep, you need 2 L of 90wt for a new LSD, plus another 1 L around 500-3000 miles if you wanna play it extra safe).

Last edited by mrsaturn7085; 07-06-2017 at 07:33 PM.
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Old 05-30-2015, 08:05 PM   #3
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Nice and thorough. Good job!

Jay
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Old 05-31-2015, 12:28 AM   #4
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Just got back from the 30 minutes of figure 8's... think I'll wait for the headache to stop before changing the oil.

The 60 degree ramps are a significantly different feeling when you corner sharply and the rebuild kit definitely makes the plates more audible. All in all, well worth the trouble!
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Old 05-31-2015, 01:05 AM   #5
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Good work!

I bought a plated diff off the yahoo Japan auctions recently and was wondering how I test it to make sure the plates aren't worn before I install it. Is this the trigger gauge you speak of?

How does the 60 degree ramp affect it? Does the diff lock quicker/earlier or something?
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Old 05-31-2015, 01:34 PM   #6
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Trigger pull gauge is a tool for firearms to test trigger pull force. It worked to test preload as well since it tops out around the upper limit for the diff. spec (~12 lbs).

60 degree ramps reduce the force needed to overcome the ramp angle; in short, the diff. becomes more throttle sensitive.

Do you know the OEM part no. of the diff. you bought? If so, I would rebuild it before installing it. I wouldn't reuse a used differential from an STI... the bellevelle washers are prone to wearing out (fairly quickly) so it's not the plates that are going to be worn, it's the clamping force of the washer.
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Old 06-09-2015, 04:00 PM   #7
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I forgot to mention, my final plate stack up gave 0.15 mm clearance which is DEAD center of the spec. Estimated initial torque is 11.65 kg-m which is roughly 85 ft-lbs. I'll jack up the rear RH side and check the wheel nut breakaway torque. This isn't the most accurate way to check, but it was ~45 ft-lbs before so I should see SOME increase.

EDIT: Initial torque measured RH rear axle nut = 85-90 ft-lbs... my estimate was spot-on!

Last edited by mrsaturn7085; 06-14-2015 at 05:15 PM.
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Old 06-13-2015, 12:02 AM   #8
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What are the disadvantages of the 60 degree diff ramps over the 45 degree?

Last edited by Fierysun; 06-13-2015 at 05:04 AM.
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Old 06-13-2015, 01:13 PM   #9
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For the rear - not many. I suppose having a diff. that activates quicker than you'd like? It's something of a moot point as the 60 deg ramps are discontinued. The Cusco/STI homologated r. diff. for the N14+ cars is a 2-way model (just like the GDB diff.) with 3 ramp angle options: 25/25 degree, 45/45 degree, 65/65 degree.

You have a lot more diverse options with the front STI or Cusco/STI LSD - from Rallispec: N12/N12b is a 2-option type (55 degree 1way ramp, 45/20 degree 1.5way ramp). N14+ is 3-option type (55 degree 1way ramp, 45/20 degree 1.5way ramp, 60/45 degree 1.5way ramp).
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Old 06-13-2015, 04:40 PM   #10
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You got me interested. This is for the Sure-Trac and not Torsen diff correct? Where did you get them? Maybe they have one more set left?
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Old 06-14-2015, 02:18 PM   #11
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This guide is for the plated diff. - Sure-Trac is a brand-name but you are correct, for the most part.

I paid about 320 EUR shipped importing the ramps from Finland (this was the last set) and about 260 USD for the rebuild kit from a private importer out of Japan (plus about 200 USD shipping, but I had other items, as well).

If you want to simply rebuild the diff. the STI kit will get you there. If you want adjustable ramp angles, the STI/Cusco diff. is probably a better choice. It is a little more expensive overall, but more importantly, it is still available.

Part no. are as follows:

ST3860055100 60 deg ramp kit
ST3900055040 rebuild kit (r.diff)
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Old 06-14-2015, 02:30 PM   #12
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Another thing I might as well mention while I'm here (now that this is a sticky):

In Japan, it is fairly common for end-users to rebuild the OEM Subaru differential with a couple of Nissan/Nismo plates/discs to increase the initial torque of the stock R180. I'll get some part numbers and basic instructions as this is a VERY cost effective way to squeak a little extra tarmac performance out of the OEM diff.

While I gather the specifics, here is some general R180 information:

http://www.cosworth.hu/?p=15

Okay - for the Nismo part mini-rebuild, you'll need the following parts:

2pc. 38426-E4610 (1.65mm Spring Disc)
2pc. 38433-RS610 (1.9mm Friction Disc)




Here is an image showing what you are doing:



Left is your pressure ring side, right is your diff. case side. On each side, you are replacing one OEM friction disc (1.7mm) with one Nismo friction disc (1.9mm) and one OEM friction PLATE (1.65mm), with one Nismo spring DISC (1.65mm).

By doing this, you are increasing initial torque in three ways:

1. You are reducing the 'stack' clearance within the diff. case by increasing the 'stack' thickness by 0.4mm total (0.2mm/side).
2. You are increasing spring pressure within the diff. case by adding a spring disc to each side.
3. (i.e. the big one) you are increasing total friction surfaces within the case from 8 to 12. This alone will increase initial torque by ~50%.

To recap, OEM plate stack-up is as follows (measurements quoted from Japanese site; my OEM diff. had different measurements on the SP & one FP):
Pressure Ring - FD(1.7mm) ・ FP(1.65mm) ・ FD(1.7mm) ・ FP(1.65mm) ・ FP(1.65mm) ・ SP(1.8mm) - Case

By placing two FP(1.65mm) on case side, Subaru has effectively disabled the third friction disc from the factory.

After doing the Nismo modification, your stack-up should look like this:
Pressure Ring - FD(1.7mm) ・ FP(1.65mm) ・ FD(1.9mm) ・ FP(1.65mm) ・ SD(1.65mm) ・ SP(1.8mm) - Case

One thing to note with this modification is the orientation of the spring disc. OEM Nissan differentials orient the sprung tabs of the spring plates and discs outward, toward the case, like this (note that the disc tabs *should* be facing outward, as well):



HOWEVER - OEM Subaru differentials orient the tabs inward, toward the pressure ring. Subaru differentials also have 4 sight holes cut in the housing that correspond to the location that the plate tabs would contact. You MUST orient the plate tabs inward, but the disc tabs can be oriented either way. Personally, I would orient them outward, as shown below:



If you were to follow the STI rebuild kit clearances, which give 65-103 ft-lbs initial torque, the Nismo modification would give you an estimated initial torque of 98-155 ft-lbs (or more!). This makes the Nismo modification great for tarmac applications where sticky tires are used.

A few general ballpark numbers you could use would be as follows:

Gravel ~50-75 ft-lbs (Cusco recommends 35-45 ft-lbs, Prodrive Group N cars ran around 55 ft-lbs)
Tarmac (street tires) ~75-100 ft-lbs (Cusco's out-of-the-box initial torque for GDB rear MZ LSD = 87-101 ft-lbs)
Tarmac (competition tires) ~100-150 ft-lbs or more

There's much more to it than this, but those numbers should give some perspective.

Another thing to keep in mind - Nissan/Nismo R180 differentials do have a number of differences when compared to a Subaru diff.; not ALL parts are interchangeable. One HUGE difference is that Nissan uses dissimilar axles splines between the LH and RH side of the car. Tweak this modification at your own risk.

Last edited by mrsaturn7085; 06-14-2015 at 05:33 PM.
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Old 07-10-2015, 08:29 AM   #13
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This is awesome! Thanks for the share!
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Old 08-01-2015, 01:39 PM   #14
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This is a great thread.
I used this for info as well
http://www.cuscousainc.com/downloads...ical_guide.pdf
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Old 08-01-2015, 07:11 PM   #15
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Yes - I *highly* recommend that document, as well! The only downside is that it gives a lot of qualitative data without throwing any of the math into the mix... but on the other hand, that makes it a lot easier to understand!
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Old 08-09-2015, 11:01 AM   #16
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Based on the numbers above, would you not recommend the Nismo modification for a street DD? I'm picking up a used r180 with about 100k miles and figured I'd rebuild it before I installed it, and I've been eyeballing the Cusco 1.5/2 way lsd but if I can just rebuild for a large cost savings I think I'd like to go that route. Thanks for the awesome information!
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Old 08-09-2015, 11:03 AM   #17
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Btw this is on an 04 r180
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Old 08-09-2015, 04:37 PM   #18
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Doing just the Nismo mod would tighten up the diff. at a good price. You would still have a worn out pair of bellevelle washers (cone springs) in the diff. but the added thickness and sprung disc would get a little bit of initial torque back. Since your remaining high mileage plates and discs are going to be worn, I wouldn't expect results like a full rebuild kit.

I started with a worn out 45 ft-lb initial torque, and ended with 85-90 ft-lbs. I imagine the Nismo mod would put you up near the 80 ft-lb range, but I've got a splitting headache and don't really want to do the math at the moment. I'll probably edit this later with an actual calculation...
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Old 08-09-2015, 06:06 PM   #19
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I need to look up prices on what a full rebuild would run. I didn't specify but that is what my question was premised on. I'd like new bearings etc
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Old 08-10-2015, 02:44 PM   #20
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~$350-400 for the STI rebuild kit, all other hardware adds $100-200.

This would include:

8 ring gear bolts
carrier gasket
side plates inc. seals
side shims
side bearings
breather vent
90wt gear oil (I like Motul 90PA)
loctite
yellow contact paint

If you need to replace the front bearings and preload shims, parts and labor will take a significant jump.

Last edited by mrsaturn7085; 08-10-2015 at 02:50 PM.
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Old 05-21-2016, 04:00 PM   #21
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very informative post !
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Old 09-01-2016, 04:35 AM   #22
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!!!!!
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Old 10-31-2016, 09:13 PM   #23
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[quote=mrsaturn7085;43472923]Trigger pull gauge is a tool for firearms to test trigger pull force. It worked to test preload as well since it tops out around the upper limit for the diff. spec (~12 lbs).
QUOTE]

What preload ae you talking about here?
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Old 11-01-2016, 01:16 PM   #24
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Quote:
Originally Posted by Motown65 View Post
What preload are you talking about here?
Rotational force on the input shaft. It's part of the FSM rebuild process.
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Old 11-01-2016, 05:28 PM   #25
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What's your opinion on an ats carbon plated lsd?
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