The LSD in my 87 Turbo II seems to be worn out. When accelerating on wet pavement I get wheelspin from my right side, and on left hand corners it wants to kick out. Is there a way to rebuild the stock LSD, or do I need to look for a replacement?

 

the S4 is a clutch type, and its rebuildable. the S5 is viscous, and its not.

 

I'm sure it's been asked, but I couldn't find an answer in my search. Will the S5 LSD bolt into an S4 car?

 

Yes.

 

as a general rule of thumb:

it was built, it can be re-built

 

For the S5 viscous LSD, there is no rebuild, there is only replace - and since it's not particularly effective or durable, and the cost is similar (iirc) to getting an aftermarket Kaaz or other much more effective LSD, any time or money spent on an S5 LSD is wasted money. But the OP should have a rebuildable clutch-type - which I would recommend against his swapping out for an S5. Even if the S5 LSD had been grandma-driven and still worked somewhat effectively as an LSD, it wouldn't take a lot of hard use to shear down the silicone and be left with an effectively open, non-rebuildable diff.

 

I work in manufacturing and am sorta in agreement with Landon. If it was put together, it can be taken apart. I hear a lot about these sealed zero turn transaxles in modern riding mowers going bad and the internet is full of guys that found a way to get into them and fix them instead of paying through the nose for a new one.

If I had a spare S5 unit I would give it a try. I've never had one out of a diff to even see what it looks like. Is the viscous clutch a crimped over metal seal? Riveted together? Anyone have some good pictures?

 

Anything is possible with enough time and money, but the only way to open the viscous coupling centre section is to cut it open, then you'd have to find a way to weld it back together, or fabricate a replacement. And why would anyone go to that sort of effort to rebuild an LSD that was crappy in the first place, and which with hard use will quickly shear down the silicone and turn it into an open diff again? The S4 clutch-type has roughly the same to slightly more locking action stock (and can be shimmed easily to get more), and while it too will also wear over time, it lasts longer and is easily and cheaply rebuildable (like, double-digit $$ if you have the tools and do it yourself. By contrast, the viscous coupling for the S5 runs $1036 from Mazdaspeed competition support (marked down from $1728, btw). For which money, other, much better choices are available.

Some info on the early Miata VLSD, which I believe is the same as the S5 NA unit and similar to or the same as the S5 turbo:
http://www.miata.net/garage/vlsd.html

 

I have clutch type with 4.3 gears. I guess I'll have to take the S5 out of the diff to find out for myself. There is no way it is sealed together at the factory with no way to get it apart. Especially if there are companies converting them to clutch type like the link you posted said.

 

No, the link says someone was converting open Miata diffs to clutch-types. Which would simply mean replacing the open diff centre section with the NA S4/GSL-SE clutch diff, which I understand is a more-or-less drop in swap - just bolt on the Miata ring gear. Knock yourself out though - and post pics - I've never seen good pics of an S5 LSD. I've been in the RX-7 community 17 years, and never heard of anyone rebuilding the viscous LSDs, either - or even trying to. People grab an S4 (which I did), get a Miata torsen (again, swap the ring gear, and it's a drop-in for NA RX-7s), but those Miata torsens are sought after in the Miata community too. Or they go aftermarket and get something much better than either of those choices.

 

Yeppers, I pretty sure this is what I have because it's an original NA diff. I don't know, Mazda went that way for a reason and I bet for a daily a good working S5 unit would suffice. If, of course, one could fix one.