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Old 02-05-2014, 11:36 AM   #1
fateo66
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Default A spotters guide to Subaru differentials

I have came to the conclusion that the Subaru Knowledge base of differentials is a bit lacking and have decided to write a little something about them and include a Pictorial to help everyone out.

While I don't want to get into too many details on what makes each diff different, here is a nice link to what Dave Anton wrote on NASIOC:

http://forums.nasioc.com/forums/show....php?t=1126026


Also here is a nice video explaining what a differential is:

[youtube]yYAw79386WI[/youtube]



I have compiled 13 different differentials for reference, which include all options for the US market and nearly all for the Japanese market as well. The only two factory options that I am missing are the 5mt front torsen that came in some late 90's RA V-limited STI's and the R180 AP Suretrac that came in the JDM Bugeye's.



To start out, here is a line up of the differentials available for a R160 rear.






And here is what a diff looks like when it breaks



Here is a version 1 viscous LSD. The unit in the center of the picture is not a mechanical unit; instead, it houses the viscous fluid and plates. This is the differential that requires two different style male axles. One side looks like a standard male rear axle and the other has two sets of splines as seen below. Please note the 4 spider gears.





Here you can see the inside of a version 2 viscous unit found in most wrx's. A version 2 VLSD is very similar in appearance to an open differential but if you look closely at the seat for the ring gear you will see that you can split the diff in half in order to have access to the viscous unit. Viscous LSD's typically are regarded as a bad unit. However, I do not feel this has to be the case. Yes a Viscous LSD is reactive in its approach to limit wheel spin because you have to have wheel spin in order to heat up the fluid inside the differential. At which time it will attempt slow down the faster moving wheel. Viscous LSDs make the car easier to drive on the street and or a situation where you have a long corner that you want to power through. The biggest down fall to the version 2 VLSD is the fact that it only has 2 spider gears and, as seen in the open diff, this becomes the first point of failure.



Here is a shot of the insides of a 2 way clutch LSD for an R160. Very similar to an aftermarket unit, this differential will lock up on both acceleration and deceleration. OEM R160 CLSDs use a bolt in axle stub and female style rear axles (US Spec).



Last up for the R160 family is the AP suretrac. This is a sealed unit so I did not feel like destroying mine but here are a few pics of what the insides looks like. The Suretrac falls into the TBD (torque biasing differential) category, which means technically its not a limited slip unit. Instead, it transfers torque to the wheel that has more load. However, it requires some load on both wheels in order to transfer the torque, otherwise a TBD will act as an open diff.




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Last edited by fateo66; 04-11-2016 at 12:05 PM.
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Old 02-05-2014, 11:39 AM   #2
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Moving forward with the TBD family, here is a line up of three other torsen style differentials. Keep in mind that Torsen is a brand name standing for Torque Sensing and these differentials are not necessarily made by Torsen.








Next I have a line up of clutch style LSDs. The two OEM units are consider a 2 way LSD where as the Cusco has the ability to be changed from a 1 way to a 1.5 way. In addition to the pre-load that you can set on certain clutch LSDs, which makes them a proactive differential, the cusco can lock up only under acceleration (1 way) or under acceleration and partially under deceleration (1.5 way)






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Old 02-05-2014, 11:40 AM   #3
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Lastly, here are a few other random pictures I took during all of this:










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Old 02-05-2014, 05:01 PM   #4
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Awesome post. This is a good great resource. I get pretty irritated when I see people selling R160 VLSDs and CLSDs as Suretracs.
Do you know if there is there is a Subaru factory R160 clutch LSD that uses the symmetrical axles instead of the bolt in stubs? I thought there might be some of those available but never able to confirm true or false.

* - hmm maybe these exist after all?

Last edited by JarHarms; 03-08-2014 at 07:51 AM.
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Old 02-05-2014, 05:13 PM   #5
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very nice. subscribed.
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Old 02-05-2014, 08:42 PM   #6
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Quote:
Originally Posted by JarHarms View Post
Awesome post. This is a good great resource. I get pretty irritated when I see people selling R160 VSLDs and CLSDs as Suretracs.
Do you know if there is there is a Subaru factory R160 clutch LSD that uses the symmetrical axles instead of the bolt in stubs? I thought there might be some of those available but never able to confirm true or false.
nope, all R160 Clsd's have bolt in stubs.
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Old 02-05-2014, 11:01 PM   #7
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And the truth! Stop playing with them vulnerable limited slip differentials!
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Old 02-06-2014, 12:02 PM   #8
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Great information, and sick 818
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Old 03-07-2014, 01:40 AM   #9
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First, thank you for taking the time to put the information and pictures together. It will be a very handy resource.

Quote:
Originally Posted by fateo66 View Post
nope, all R160 Clsd's have bolt in stubs.
Are you certain on this? From what I have read, this sounds right for all US based CLSD's, but the Ver1/2 STi had CLSD's and I thought they were interchangeable with the early style VLSD units. Meaning they required the dual spline axle. I think the part number is ST3860055000.

From which yr/model did you source your r160 CLSD?

-Rob
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Old 03-07-2014, 07:24 AM   #10
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@rob I thought those STi's had R180's.
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Old 03-07-2014, 09:21 AM   #11
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Quote:
Originally Posted by rob View Post
First, thank you for taking the time to put the information and pictures together. It will be a very handy resource.



Are you certain on this? From what I have read, this sounds right for all US based CLSD's, but the Ver1/2 STi had CLSD's and I thought they were interchangeable with the early style VLSD units. Meaning they required the dual spline axle. I think the part number is ST3860055000.

From which yr/model did you source your r160 CLSD?

-Rob

I'm 100% positive on this and honestly that mis-information is the exact reason why I made this thread. If you see any axle that has double splines it's a V1 VLSD. The inner spline drives the Viscous coupler.
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Old 03-07-2014, 02:18 PM   #12
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Excellent!
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Old 03-07-2014, 02:33 PM   #13
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STI Type RA Ver.1 and 2 used an R160 with a clutch type LSD and the double splined type rear axles.

The GC8 Viscous type R160 with double splined axles were used from Ver.1-3 in Japan and possibly later than that outside of Japan.

The R160 Suretrac LSD was used first in certain auto trans WRX models in Japan (possibly in certain special edition?) in Ver.3 and then all the R160 WRX and STI from Ver.4 to 6.

At some point around MY2000 the viscous R160 LSD was changed such that they used the same single spline design left and right as per all the R160 Suretrac models.
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Old 03-07-2014, 02:41 PM   #14
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Quote:
Originally Posted by Dave_RalliSpec View Post
STI Type RA Ver.1 and 2 used an R160 with a clutch type LSD and the double splined type rear axles.

The GC8 Viscous type R160 with double splined axles were used from Ver.1-3 in Japan and possibly later than that outside of Japan.

The R160 Suretrac LSD was used first in certain auto trans WRX models in Japan (possibly in certain special edition?) in Ver.3 and then all the R160 WRX and STI from Ver.4 to 6.

At some point around MY2000 the viscous R160 LSD was changed such that they used the same single spline design left and right as per all the R160 Suretrac models.
Thanks Dave.

This is how I understood it to be.

-Rob
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Old 03-07-2014, 03:16 PM   #15
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Quote:
Originally Posted by Dave_RalliSpec View Post
STI Type RA Ver.1 and 2 used an R160 with a clutch type LSD and the double splined type rear axles.

The GC8 Viscous type R160 with double splined axles were used from Ver.1-3 in Japan and possibly later than that outside of Japan.

The R160 Suretrac LSD was used first in certain auto trans WRX models in Japan (possibly in certain special edition?) in Ver.3 and then all the R160 WRX and STI from Ver.4 to 6.

At some point around MY2000 the viscous R160 LSD was changed such that they used the same single spline design left and right as per all the R160 Suretrac models.
Dave, not that I don't believe you because you have a plethora of knowledge but do you have any pics of a double splined axle used in a clutch R160 LSD? Or can you tell me what the inner spline is used for? Subaru has had R160 CLSD's in the US since mid 80's and they all use symmetrical stubs.
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Old 03-07-2014, 03:21 PM   #16
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I do not have pictures. But I have researched all the parts data and the double splined axle part number is used on all R160 from Ver.1 to Ver.4 regardless of the LSD uses. I should also point out that there are two different Suretrac units. Ver.3/4 units are designed around the double splined axle. Ver.5/6 are designed around the single splined axle.
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Old 03-07-2014, 03:22 PM   #17
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I don't know what the 2nd set of splines is used to drive, if anything, on clutch and Suretrac units.
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Old 03-07-2014, 03:41 PM   #18
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I should point out that I know all this because we were asked to build one of the first US Spec WRX's for rally here and there were not a lot of aftermarket LSD options at that time that we could get quickly....we purchased a Quaife unit which at the time was advertised to fit all WRX's but it turned out to have been designed around the double splined axle. They only used the larger OD spline set but the depth, clip dimension, and clip groove depth were such that you could not install a single splined WRX axle on the side designed for the double splined type. So we had to buy the double splined inner joint from Japan to build special axles. I did a lot of research in the process of resolving that issue back in 2001.
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Old 03-07-2014, 03:49 PM   #19
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If I had to guess, I would say the inner spline does nothing for the non-V LSDs however they needed to be manufactured to accepted them for the purpose of part interchangeability between the same generation WRX/STI/STi-RA models.

Dave, what is the part number for the Ver3/4 Suretrac units? Is it either of these?
ST3841066000
or
27022AA010

-Rob
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Old 03-07-2014, 11:13 PM   #20
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I've got an R160 CLSD on the shelf that does not have a threaded center for the bolt in stubs. It does not appear to have any smaller spline section deeper inside either. I have also put a similar unit into service using standard axles. I will edit this post with some pictures that will help illustrate.

Bolt in stubs have a larger diameter (tried to insert a spare set also on the shelf).

Jay
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Old 03-09-2014, 11:29 AM   #21
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Here is a link to an album of pics I snapped of this R160 LSD that accepts normal axles.
https://www.dropbox.com/sc/8glsys6e2isq1e6/sM_3lhuljN

I do not know the original application.
Jay
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Old 03-12-2014, 06:13 PM   #22
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Sub'd for referencability and awesomeness
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Old 03-12-2014, 06:38 PM   #23
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Pretty cool
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Old 07-10-2014, 12:51 PM   #24
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Whoa! Thanx for the comprehensive photo shots! Cool Laila!
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Old 07-20-2014, 12:46 PM   #25
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Awesome post by the OP!
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