[adey]

I know this has been discussed before (I probably saw it on FA, the search on zilvia came up with nothing useful), but I think it would help to have an easier-to-understand and more recent version of it up here, especially since there have been so many LSD (limited slip differential) topics recently.
With the growing popularity of drifting and the growing sales of LSD (new and used) there still seems to be a mist hovering around the somewhat complicated topic of LSDs and which ones will fit in our cars.

I will share my assumptions (I don't know any of this for sure) about the usability of different S-chassis (read: NOT J30 or Z32 differential parts) between JDM and USDM S13 LSDs, side shafts ('output shafts' or 'axles'), flanges (flange), pumpkins and LSD, VLSD, and open differential units.
In other words, I DO NOT KNOW WHAT I'M TALKING ABOUT, AND SEEK YOUR CORRECTION OF MY MISINFORMATION. (so please, don't take any of what I say too seriously.)

end introduction
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begin (mis)information

Glossary:
- LSD: (actual "hat" shaped thing that goes INSIDE the outer shell; the "guts" of a pumpkin, if you may.)
- Pumpkin: Outer "shell" of the differential. AKA Differential Case or Housing.
- Output Shaft = flange(s), output flanges; the piece that sticks out of the differential. 2 flavors: 3 tab, 6 hole USDM style, and the 5-tab 5-bolt JDM style.
- Axle: the long piece that connects to the hubs via splines that are often rusted together. This piece bolts to the output shafts of the pumpkin. (AKA "Half shafts"?)

Currently in the market (well, sort of) for a 2-way clutch type (aka mechanical?) LSD, I have come across a number of problems surrounding which axles (aka half shaft?) that I will need and what flanges will mate up with what axles.

For example: I'm currently looking at a 2-way LSD that includes the whole Subframe assembly; that is, all arms, hubs, rotors, calipers, shafts (aka axles), and the LSD (pumpkin) itself.
With this, it is "easy" to do, because I have everything I need:
- the JDM VLSD pumpkin with a 2-way LSD in it -- this has the 5-bolt star shaped flanges sticking out,
- two JDM 5-bolt star-shaped axles.
I'll go over why this is good further down the post.

What's most sought after stateside is not so much an actual LSD so much as these 5-star axles. The S13 USDM VLSDs (apparently quite hard to find used) came with 6-bolt (triangle shape) side flanges, and will bolt up to open differential axles which should also be 6-bolt triangle patterned.
(Unfortunately, I'm not sure of what the USDM S14 axle bolt patterns are like {for either open or vlsd}... so I'll let someone else touch on that.)

However, the JDM VLSDs (or VLSD pumpkins with after market LSD) which seem to be more abundant, came with 5-bolt star shaped patterns... which do not bolt up to either S13 open or VLSD axles. (MAY bolt up to S14 axles, although I don't think the rear pumpkin cover will bolt up to USDM S14 subframe)

So. You have an Open diff and what a 2-way LSD. What do you do?

(S13)
- You need to find an S13 that had a VLSD, grab the pumpkin, swap out the internals of that (with your LSD), replace the RIGHT (I think-- whichever side is LONGER) flange with another LEFT (shorter) flange from another VLSD and replace your open diff pumpkin with this new frankenstein-of-a VLSD (now with 2-way LSD inside) pumpkin into your S13. (about on par with third method outlined below in terms of difficulty) The pumpkin with modified output flanges will mate up to your stock USDM axles.

- OR: find a JDM pumpkin with 5 bolt flanges, get JDM 5-bolt axles to go with it. Take out your current axles (can be a SERIOUS pain in arse if your splines have rusted together), replace your axles and pumpkin with JDM units. (Depending on how big of a headache pulling your axles give you, this could be the hardest way to do it)

- OR: {probably easiest to do?} With JDM LSD & pumpkin, open up the pumpkin and replace both side flanges with USDM VLSD left side (short) 6-bolt flanges. (that's right, you need two short ones-- US VLSD flanges were different lengths.) Then bolt this up to your stock 6-bolt, 3-tabbed axles. (have the flanges swapped out by a shop or at least someone who's done it before, it's important that all internals are kept in good alignment/spacing.)

There are other ways to get an LSD into your car, but I think the 3 up there are pretty much the most popular and/or convenient ways to do it. If you can grasp the concepts of which cars have 6-bolt tri-tabbed (triangular, if you may) flanges and which have 5-bolt 5-tabbed star shaped flanges, it should make a lot more sense.

end of my babble.
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Umm... that said, can anyone confirm for me that it is indeed two of the SHORTER (LEFT) VLSD flanges that are needed to work with an aftermarket LSD, and that will bolt up with stock axles?