So, I bought my 1990 Miata a couple months back or so, and when I bought it, the previous owner said that the owner before him put in a 94+ Torsen LSD. I wasn't too Miata savvy and didn't take a very close look at the diff. I went to a local autoX yesterday and the car didn't feel like it had a LSD, but thought I could be wrong, but figured I would take a look at it today.

I crawled underneath the car, and here is what I found:







After looking at the differential spotters guide:
http://forum.miata.net/vb/search.php?searchid=5992066&pp=25&page=2

I realized a few things about this diff:

-It has no rubber pinion damper.
-The stubs have flange ears, but they are all equal size.
-Diff case is vented.

I also noticed that my speedo was fairly accurate, making me think the stock 4.30's could be in there unless someone swapped out a speedo gear.


Either way, I'm starting to think this is actually a 1.6L open differential. Without tearing it apart, any other way to tell? Were some of the 1.6L open diffs vented?

Any help on identifying this differential would be greatly appreciated!

-Brandon


P.S. If my assumptions are correct and the previous owner was mistaken, not only am I a little bit pissed right now, at least there's a bright side, no more running in STR, as this would bump me down into STS... but when I go to boost it, that just means more money to be spent in beefing up the rear end. *sigh*.

After looking at this a bit further, I also noticed the diff carrier arms are bent:




Which based on this pic of the 1.6 & 1.8 diffs:
http://www.solomiata.com/images/rearcomp.jpg

It further strengthens my theory that it is in fact a 1.6L differential, and is open.

Anyone have a couple personal pics they can post up? Or at least confirm/deny my theory?

The guys over on Miata.net apparently agree with me, it's a 1.6L open.... man, I'm feeling cheated right now, but it makes a lot more sense with the car the car applied power when driving hard. Can't say I'm very happy with the previous owner right now...

Looks like I'll be re-classing my car to run STS.

It is possible since you said the PO mentioned to you the previous owner before him (2 owners ago) swapped the diff it was the PO you bought it from who was actually lied to and he just never knew any different or investigated it.

At least now you can drop to a class you're more competitive in, but more money will have to be spent when upgrading.

chickenwafer wrote:It is possible since you said the PO mentioned to you the previous owner before him (2 owners ago) swapped the diff it was the PO you bought it from who was actually lied to and he just never knew any different or investigated it.

At least now you can drop to a class you're more competitive in, but more money will have to be spent when upgrading.

Yeah, I don't think the PO intentionally lied to me, he seemed fairly ignorant to be honest. I think there was probably some communication error, as I think the owner before him probably had a torsen on there for a while and removed it/sold it prior to selling the car.

Either way, it's a pro and a con, be more competitive in autoX, but spend more money down the line... oh well, at least if I decide to upgrade in the future, instead of getting a 4.10 torsen, I would just hold out for a later model 4.30 torsen. Always gotta try and look on the bright side right?

Even without going out and jacking up my car to take pics, I'd have to say that diff looks exactly like mine. You can test for LSD by lifting the rear wheels off the ground, putting it in neutral, and spinning one of the wheels. If they both turn the same direction, it has LSD. If they spin opposite directions, it doesn't.

erod550 wrote:Even without going out and jacking up my car to take pics, I'd have to say that diff looks exactly like mine. You can test for LSD by lifting the rear wheels off the ground, putting it in neutral, and spinning one of the wheels. If they both turn the same direction, it has LSD. If they spin opposite directions, it doesn't.

Do you have an open diff or a VLSD? Or do you know?

I agree with Erod. Jack the car up and spin the wheels, easiest way to see if it's a LSD. Both wheels will spin the same way, if they don't it's open.

I'm pretty sure I have an open diff. The VLSD was an option I believe and I don't think I have it, but I'm not 100% sure. I've never done the test for it. Just make sure you have the car in neutral when you do the test. Even with LSD, if the driveshshaft is constrained (car in gear), it will behave like an open diff.

erod550 wrote:Even without going out and jacking up my car to take pics, I'd have to say that diff looks exactly like mine. You can test for LSD by lifting the rear wheels off the ground, putting it in neutral, and spinning one of the wheels. If they both turn the same direction, it has LSD. If they spin opposite directions, it doesn't.

RX-7 Chris wrote:I agree with Erod. Jack the car up and spin the wheels, easiest way to see if it's a LSD. Both wheels will spin the same way, if they don't it's open.

Even though pics/documentation & members over on Miata.net already confirmed it was a 1.6 open diff, for shits and giggles I took 3 minutes out of my evening, grabbed my floor jack & a jack stand, jacked the car up/disengaged e-brake, spun one wheel, and sure enough, the other one spun in the opposite direction

So yeah, it's confirmed, it's an open diff from a 1.6.... with how the car applied power yesterday, it makes more sense now.

Looks like I needlessly classed myself into STR yesterday haha, that'll teach me to take the word of a previous owner without double checking something myself!!

BTW, Chris, I heard you come out and play in STS every once and a while... wanna join me in a couple weeks?

I actually haven't raced my car yet. There is another guy with the same car in STS that does race though. I'm hoping to start racing my car soon. As soon as I get my new motor mounts in I think the car will be ready to go.

My car has a VLSD, hehe. It really sucks that the guy lied to you like that.

RX-7 Chris wrote:I actually haven't raced my car yet. There is another guy with the same car in STS that does race though. I'm hoping to start racing my car soon. As soon as I get my new motor mounts in I think the car will be ready to go.

My car has a VLSD, hehe. It really sucks that the guy lied to you like that.

Nice! Look forward to having someone out there that drives as slow as I do haha!

Yeah, a good portion of the reason I bought the car was because I was under the impression it had a torsen in it.... feeling pretty cheated at the moment. Oh well, live and learn. I'm going back to a former rule of mine: don't buy cars that were previously modified.

If I find one for cheap, I might put a STS legal 90-93 VLSD in it. We'll see.

I would talk to flyin' miata about the VLSD. they probably have a bunch and they may not cost all that much.

RX-7 Chris wrote:I would talk to flyin' miata about the VLSD. they probably have a bunch and they may not cost all that much.

Yeah I checked their salvage section, but no dice, they don't have any 1.6 4.30 FD VLSD's in stock right now. Found a guy in Highlands Ranch that thought he had a VLSD, but as it turns out, it was an open diff. There's a few of them on eBay for $300-$400 + shipping, but that's a bit more than I'm looking to spend on something I'm just going to sell eventually anyway.

I'll keep my eyes open.

I think the VLDS out of the 84-85 rx-7 also fits but you may want to do a little more research on what that takes.