Now that's a good Miata day!
Somehow, every time I glanced at the differential of my Miata I saw the ears on the flanges. Ah well, open differential.
Today, doing totally unrelated work I glanced at the differential and saw the wedgie pieces. Say what! I know what that means! Double check the miata reference pages, yep those are the flanges for the limited slip rear. No wonder why the axles were so hard to turn when I did the brakes the other day.
Yippee!!!
Yay. Now you can't run in ST2 for auto-x which specifically says that you CAN run a Miata but also says that you CANNOT run a car with a limited slip other than a viscous type. So you can run a Miata in that class, just not yours (even though you didn't modify the differential).
Now, go do yourself a burnout. A big, tire-hoppy, two-wheel burnout.
Foxtrapper, you just reminded me to check mine. Guess what? You made my day, too!
Ah, but you CAN run in STR!
imagine my surprise to find one in a Town Car 
I found one in a Vega I drove in college. It didn't help.
If he can spot the differential by the flanges on the stub axles, that means it's a 1.6 viscous. So he can still run in ST2 just fine.
BTW, the best way to tell is to simply look for different flanges on each side. 1.6 viscous diffs have different flanges left and right, every other Miata diff (1.6 or 1.8) has symmetrical flanges and there's no external way to identify them.
Same thing happened to me - my wife's 1990 has a viscous. I found out by spotting the flanges as well.
I have found several locker rear ends in various cars with my stick welder.
I put a trac lok in my Crown Vic, it helped alot.
(finished second in the 2008 Detroit Region rallycross championship)
My Vega drove well enough for a school car. It was a '75 Kammback (wagon), with a GT dash, Holley/Weber carb, etc. Once I could afford some Radial TA's, it handled a lot better.
Hmm..
Usually I just look at the build sheet 
Shawn
Miatas don't have that cute list of all options printed on a sticker attached to the car the way that GMs do. Pity, it would dry up all the "I think I have a Torsen, how can I tell?" questions.
In reply to Keith:
That stinks..
Too bad there isn't an easy way to decode it by cowl tag / vin tag.
Maybe that's a service Flyin' Miata should look into as the cars get on in years.
Even GM owners don't always get lucky. The build sheet is usually in three places, under the pass seat, behind the rear seat and above the gas tank. Most of these places will have been tampered with or have seen a lot of water in the last 30 years.
Shawn
Now I'm going to go hunting this Thanksgiving on any of the GM cars that come to my parents house. I want to find this sheet you speak of.
I thought you could call Mazda with your VIN and they can tell you the options that originally came on the car. At any rate, when you call Mazda one of the menu options is to hear the Renesis engine, or you could last year sometime, anyway.
BTW, I found my Limited Slip last year by looking at the flanges too!
I am very lacking in all thing Miata but don't you know it by driving it if it is a LSD?
In reply to dean1484:
Psh. We don't actually drive them, we just collect them!
In reply to confuZion3:
Disassembly is usually required to find a build sheet. The experience I have is from F-body cars only. Norwood assembled cars usually have two, sometimes three build sheets in various locations. Van-Nuys cars usually have one, sometimes none.
If it's a 1982-ish and newer GM vehicle, an option sticker should be on the doorjamb or under the hood.
The option codes on the sitckers will let you know what it has.
keep in mind that there is a very easy way to figure out if you have a LSD....
get yourself somewhere where the Man won't see you and lay a patch... if you leave twin tracks it's got the rear end locked up... peg leg.... no LSD...
Option stickers, that's what I was thinking of. Very handy as I went to find out just what was in my donor Camaro.
FM would love to provide the service of telling people if their car has* a Torsen. But the information isn't in the VIN. It's only in Mazda's database, or by figuring out just what the option package on the car is. Mazda has always been able to tell people. Same with other options. No build info is hidden in the Miata VIN.
None of the LSDs found on factory Miatas are terribly obvious in their function. Most of us at FM can spot a Torsen from some subtle clues in the parking lot, but generally speaking they're transparent in operation.
*of course, you can only tell if a car had a Torsen, really. If it's been swapped since the car left the factory, then you need to figure it out for yourself. And a test drive is the easiest way to tell. All you need is two surfaces with different traction levels and an accelerator pedal. That's what I always tell people, but they seem to prefer more complex methods involving pulling out halfshafts and the like.
wbjones wrote: keep in mind that there is a very easy way to figure out if you have a LSD.... get yourself somewhere where the Man won't see you and lay a patch... if you leave twin tracks it's got the rear end locked up... peg leg.... no LSD...
With IRS and both wheels with the same traction level, that won't necessarily tell you anything. IRS cars don't unload one side the same way that live axle cars do.
When you find the code tag on a GM car or truck, G80 is often the code for limited slip axle. G92 is performace ratio limited slip. Look for code tags in the trunk on the spare tire cover, under the center console lid, or in the glove box. The paper build sheets are for older cars, pre-1980 roughly. Do a search for RPO codes and you will find lists and where to find the tag in each car.
I've had various limited slips, lockers and other things. You can't just go by the twin strips of black. My old 740 wagon would do that with an open differential quite nicely. The Miata has a viscous limited slip, so I don't know that it will do a very good job of laying twin strips.
In any case, with this particular car, I assumed it had an open diff (most do), wasn't going to drive like an idiot on the test drive, and hardly drove it when it came home. I only just got it in the road the other week. I had noticed it wasn't breaking the inner tire free when I expected it, and was starting to wonder if maybe I'd gotten lucky.
Keith wrote:wbjones wrote: keep in mind that there is a very easy way to figure out if you have a LSD.... get yourself somewhere where the Man won't see you and lay a patch... if you leave twin tracks it's got the rear end locked up... peg leg.... no LSD...With IRS and both wheels with the same traction level, that won't necessarily tell you anything. IRS cars don't unload one side the same way that live axle cars do.
ok guess I need a quick lesson here.. with all my open dif vehicles if I dump the clutch all I get is a single strip of rubber... in cars w/ LSD there is always 2 strips.... I just never have seen an open dif car lay 2 strips...
maroon92 wrote: I put a trac lok in my Crown Vic, it helped alot. (finished second in the 2008 Detroit Region rallycross championship)
But you never cleared all of the cones off the south end of the lot with your tailpipe, didja Nancy?
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