Wheels that slip find new grip.
When I purchased my car, it came equipped with an aftermarket rear differential - the Tomei 2-way LSD. A popular choice for drifting, the 2-way designation means that under power AND under deceleration the rear wheels are locked together for increased grip. It's a very predictable setup (off the accelerator, the wheels can still turn at different rates going around a corner), however it makes a very loud "crack, crack, CRACK!" noise every time you go around a corner under power UNLESS you are drifting around a corner. In other words, it's a bit annoying to drive around on the street with. Luckily, there is an OEM Nissan solution that provides increased grip over the stock open rear differential without the noise penalty. I am referencing the Nissan Helical LSD from the S15 Spec R, as pictured above.
I was able to source this rear differential from another Nissan enthusiast on Craigslist here in Chicago. Luckily, this diff came with both of the matching side yokes - these are a different size than the stock S13 side yokes and the diff will not fit without them. After collecting the most important parts, there were still a few things on my shopping list.
Also from Craigslist, I was able to source a spare Nissan S13 R200 rear diff and case. It would be necessary to pull the stock "open" diff from this case and replace it and the side yokes with the S15 HLSD units. I also sourced new bolts for the ring gear (like flywheel bolts, these are one time use bolts that need to be replaced), a gasket set, side seals, and Redline 75W90 GL5 gear oil.
Once again, my Uncle Jim was kind enough to help with some of the finer points of this installation, including installing the side seals and checking the ring gear backlash and side play. Getting these steps correct is necessary to avoid strange whining noises and leaks from appearing down the road.
Here, you can see the new S15 center section installed with the stock ring gear. Retaining cap bolts have already been torqued to spec, and the ring gear backlash and side play has been measured - thankfully it was within acceptable factory tolerance.
Old diff out, new diff in! The old diff with the Tomei 2-way LSD will go back on the shelf. Some day I may reach a power level where a weapons-grade piece of hardware like that is actually necessary.
The new diff case installed and ready to party. Thankfully, I was able to complete this entire operation in one day. Test drive went smoothly, with no unusual sounds or leaks. Just smooth, silent grip around corners.
Anybody who says the S15 Helical LSD is not a good upgrade needs to check their source. This diff was factory spec in the highest evolution of the S15. It's also the diff of choice for the "Hachirokumeister" on YouTube, who routinely catches air and chases down Porsches on the Nurburgring in Germany with his 200SX. He has managed to unlock incredible potential with carefully chosen mods to his car. His videos and talent behind the wheel are as big an inspiration for me as the original RUF Yellowbird Nurburgring video.