i have a 96 miata and want to know how to tell if its got an lsd. according to the american specs it should have one but im not so sure is there any way of telling for certain?
This might help: Differential Spotters Guide
I have driven a few cars with LSD and the scary one was a full race mini it just dived all over the place, my 1.8s has LSD and I know it is working, I have to make a sharp turn from a dangerous junction every morning to work and have to accelerate smartish if some prat is doing 80mph round the bend by this junction, the back end gives a few small stutters and just grips and goes, if you dont have one you will make lots of smoke!! Basic test but will answer your question instantly.
Regards
Geoff
If the thing is mechanically 100%,take it somewhere quiet. Dial up 5000 revs, dump the clutch[:O]
One black line, it’s an open diff. A “No11”[;)] = LSD. The clutch might stink a bit but will recover if it’s a good’un.
A “No11” Here 
IF you have got one from Mazda then it would be the Torsen which is not a diff. that locks when one wheel spins. It Tor(que)sen(ses) the car going round a corner and puts more power to the outer wheel. It’s fine on dry roads but not my cup of tea with power in the wet when it behaves just like an open diff. just as soon as a wheel spins. Perhaps someone here (certainly not me) could tell you how to identify a Torsen from the outside of the diff. case. Robbie Roadster? 
http://www.torsen.com/general/general_faq.htm
I can tell from VIN number/vehicle spec but not by sight, sorry.
I believe that my R-Limited has a LSD but I’m not sure (from reading around the subject and from comments in this thread and others) whether it’s a good thing to have!
Isn’t a way of seeing if you’ve got one to jack up the rear of your car and spin a wheel - if they both turn in the same direction you have got a LSD. Or is that something else?!
how do you tell from VIN?
That test sort of works for viscous LSDs, might work for Torsen LSDs, and can give a false positive for open diffs.
So not that reliable a test.
If you can’t tell from driving your car whether it has a LSD or not then you don’t need a LSD.
That’s a helpful statement. 
If, like me, you have no idea of the characteristics that a LSD give to a car’s handling how are you to know?
Maybe you could answer the question without resorting to such elitist condescension?
Hardly elitist as I can’t tell from normal driving if a car has an LSD or not [:D]
I can spot a welded diff right away (to be fair so can anyone - at low speeds it feels like you have triangular wheels), but not a viscous one, or a Torsen. I have an RX7 which may, or may not, have a Torsen diff. I don’t know which it has, I don’t need to know either as I like it how it is.
My point was - if it doesn’t have a noticable impact on your car they way you drive it, then you don’t need to remove one if you have one, or add one if you don’t. In other words - if you are happy with your car, does it matter what label the mechanical bits have?
There, humble enough for you? I was just trying to spread some contentment. There are good solid arguments for and against LSDs on road cars.
I have had lsd (locking diffs.) in all my cars since 1974 and they were all rear drive V8’s with plenty of torque to overcome the tyre grip.
Basic description only … as soon as one wheel slipped, the diff. locked so that both rear wheels were driven at the same speed. So, either you got traction again or they both spin depending on the total ammount of grip. This meant that you continued in a (roughly) straight line where you wanted to head. I for one preferred it but I don’t think I would be in the majority here. If you don’t have one and want to go ahead and buy one I’d get a Kazz or Quaiff (too lazy to check the spelling).
This Torsen (more popular with today’s car manufacturers) is the first of this form of lsd that I have ever had so bear with my (5 year)experiences of it. When one wheel spins that’s it, if you keep your foot planted you will get the tail wagging if you don’t lift off pretty smartly, the same as an open diff.
The Torsen however is less likely to slip in the first place when compared to either the locking diff. or the open diff. That’s because it is biased to send more torque to the outside wheel when cornering (the one with the greatest load/grip). Most of the time it’s getting out of ‘T’ junctions where you will notice it more frequently. The Torsen is too quiet to notice but the ‘lockers’ can be clunky at times.
Hope this helps.
That would be “Kaaz” and “Quaife”.
The only LSD that Quaife make for the MX5 is an ATB diff, which is essentially Quaife’s own version of a Torsen diff. As such the ATB diff never fully locks and is as useless as a Torsen when one wheel loses grip completely.
The Kaaz diffs are traditional ramp/plate diffs and are available as 1, 1.5 and 2 way versions. Cusco can also supply ramp/plate diffs for the MX5.
Yes, humble enough… 
…and I apologise that I read your comment as a bit of “don’t you worry your pretty little head about it” nonsense! Sorry…
What I was getting at though is this - I love the way my car drives and it doesn’t bother me really whether I have a LSD or not but I would like to know, in layman’s terms, what those solid arguments for and against one are and, as importantly because I think I do have one, what are the handling characteristics that I might expect to notice from time to time? I’ve read somewhere that they’re a nightmare on icy roads but in what way are they a nightmare and what should I do to avoid problems?
That’s the sort of info that I’d find useful, and maybe so would people who are unsure if they have one at all.
If you have a VLSD or Torsen device then they are a nightmare on icy roads in pretty much the same way as an open diff - i.e. they are useless in these conditions since they never fully lock.
Therefore to avoid problems on icy surfaces:
-
Fit winter tyres
-
Carry a large bag of sand or aggregate in the boot
-
Drive carefully
Failing this, walk or catch the bus.
(In view of recent tensions in this thread, all of the above meant in good humour, no offence intended!)
With a proper locking diff I guess there may be a tendency for the
back end to drift/kick out on loose surfaces?
So in ice and snow be careful! Is that the same in the wet?
Presumably there’s a comparable benefit in the dry?
(No tension, not here anyway.)
Imagine you are driving round a low speed corner and applying some power.
If you have an open diff and apply too much power there is a chance your lightly loaded inside wheel will spin, stopping you from acellerating. Noisy but not dangerous.
If you have a LSD the power will be juggled between the two rear wheels, so you can acellerate. This is fine up to the limit of rear grip, at which point the back end of the car rotates away from the corner and you have to start flapping at the wheel. Faster but more dangerous.
So unless you are expecting it the LSD could have just caused an accident, where an non-LSD car would have just spun a wheel.
However, you can get oversteer from lifting off, turning in to fast, braking, or just about any clumsiness, and once you have oversteer it can be significantly easier to control with some form of LSD because an open diff could just decide to spin one wheel at any time.
However, again, most LSDs are progressive in the way they limit differntial speeds between the wheels, so if you are close to the edge you may not notice anything happening at all. So not as dangerous as all that.
The exception to this are clutch/plate type diffs which lock the two wheels together when throttle is applied (or lifted off, depending on model) where the transition between open and full locked can be harsh. And then there are welded/spool diffs, which have zero slip all the time and can cause massive understeer as well as massive oversteer, often on the same corner with not much warning. You can drive these safely on the road, but you have to be a bit careful.
I do a bit of competitive drifting and having tried various cars at the extremes of oversteer I’d avoid open diffs for paying around with oversteer, although it can be done. But my road car has an open diff, and I like it that way.
Edit to add: wet or dry, the charateristics are much the same, but everything happens at lower speeds. When it’s snowy I use my car with a welded diff, which has great traction for pulling away, and is very controlable when the grip runs out. Plus it has a roll cage and harnesses, and you’d be mad not to use those during crashing season. I’ve no idea how LSDs react to ice and snow, as I’ve only ever used open or welded diffs in those conditions.
I’ve no issues with the Torsen in the dry but it’s all too easy to snap sideways when using full throttle to overtake in the wet. Sometimes it’s ok, sometimes not; probably dependant on the bitumen grade.
There’s just too much torque (200#+) so the best I can do (apart from modifying my driving) is always to use premium wet weather rubber.