papak Posted June 16, 2019 Share Posted June 16, 2019 My Birkin uses a Subaru R160 viscous LSD. While at the track a couple of weeks ago, I lost about 90% of the forward drive in a 3rd gear sweeper. It was initially felt like a burned clutch (but on recollection, there was no “burned clutch” smell). After removing the engine, the clutch, slave cylinder and spacing criteria all seem spot on. After eliminating the clutch, the only remaining culprit seems to be the diff. When I initially built the car, I thought that a viscous LSD would be sufficient for the motor (2.3l Duratec with ITBs, 9.7:1 and Stage 1 cams, maybe 180-190 hp). I’m still trying to figure out a productive way to check the LSD. When the driveshaft is turned, both rear wheels rotate in the same direction as they should. The question is if the do so under load. I was able to drive the car into the garage from the trailer but it didn’t feel like it was fully connected. Not sure quite how to describe it any better than that. Any ideas? Link to comment Share on other sites More sharing options...
Croc Posted June 16, 2019 Share Posted June 16, 2019 A number of people I know use the same diff with more hp - it should be sufficient. They were built really tough. I have heard and seen Subaru viscous diffs overheating on track (in a 300hp Subie) and then losing drive as you describe but they all come back normal feeling after cooling down. Did yours come back or is it still feeling wrong? One other idea, change the diff oil and try again. You may have overheated the lube and it has broken down at a molecular level so that it no longer provides the right lube qualities for the diff to lock properly. I have seen that happen in a GTR. Link to comment Share on other sites More sharing options...
papak Posted June 16, 2019 Author Share Posted June 16, 2019 According to the Subue forums, the viscous unit is sealed and non-repairable. It is filled with a silicon based lube with unique shear qualities. The diff itself uses GL-5. In my case, it seems as though the silicon stuff has been fried. Link to comment Share on other sites More sharing options...
Croc Posted June 16, 2019 Share Posted June 16, 2019 Hmmm....so now the silicone lube has all new shear qualities! Link to comment Share on other sites More sharing options...
papak Posted June 16, 2019 Author Share Posted June 16, 2019 It seems so. Link to comment Share on other sites More sharing options...
papak Posted September 3, 2019 Author Share Posted September 3, 2019 The viscous LSD was definitely the culprit. After some networking, I purchased a freshly rebuilt R160 with an AP Suretrac LSD from ZF Design (thezfdesign@gmail.com) outside of Denver, CO. They rebuild Subaru drivetrain components for the offload crown over there. Zach Fothergill was quite knowledgable about the compromises between the various LSDs. He can also provide any of the final drive ratios offered by Subaru. At any rate, while the drivetrain was out of the car, I took the opportunity to replace the front cover of the engine (slight crack) and re-index the cams. Crower originally ground them with 4 degrees of advance for emissions compliance. I added adjustable cam sprockets but the indexing was slightly off as this was originally done with the engine installed in the car (either way, it is definitely a two person project). With the cams now indexed to a zero datum, I should theoretically have a bit more torque. As the car hasn't been dynoed, I really don't know. It does seem very slightly smoother under acceleration. Gratifyingly, no leaks after the first weekend of running after everything was back in the car. Great to be back on the road again! Link to comment Share on other sites More sharing options...
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