NA Miata Diff Interchangeability

[MaRcOp01o]

Hello All,

I am looking to get a LSD for the Yata. I have a 97 and I was wondering what year Miatas can "plug n play" into my Miata.

[bogaut]

94-05

[DarylSibcy]

94-05 is "Plug and play", roughly.

You'll need the propshafts, driveshafts and the whole rear differential from a 1.8, ideally one that already has an LSD in it.

From someone who's gone through the process, I'd recommend paying the extra to buy everything together that's been pulled out of one car. It can become a minefield buying the diff, rear housing and etcs as Mazda made changes along the way. Another thing, decide what final gear you want too. The earlier NA 1.8's have a 4.1:1 ratio whereas the later NB models have a 4.3:1 ratio because most had six speeds bolted up to them. Stock 1.6 diffs are 4.3:1 for reference.

I went with the NB's 4.3:1 because I've stayed N/A and didn't want taller gears. If you opt for boost the popular choice is swapping in a 3.6:1 ratio ring to compensate for the added power.

In short, decide on your final drive ratio, then buy everything together to avoid any headaches. I'd recommend to clean everything up and replace all the seals "whilst you're in there", it'll give you piece of mind that you won't need to touch it again for another 100k miles. Good time to get new diff bushings too, most diffs won't have seen a rebuild during their lifetime either.

HTH bud!

[MaRcOp01o]

94-05 is "Plug and play", roughly.

You'll need the propshafts, driveshafts and the whole rear differential from a 1.8, ideally one that already has an LSD in it.

From someone who's gone through the process, I'd recommend paying the extra to buy everything together that's been pulled out of one car. It can become a minefield buying the diff, rear housing and etcs as Mazda made changes along the way. Another thing, decide what final gear you want too. The earlier NA 1.8's have a 4.1:1 ratio whereas the later NB models have a 4.3:1 ratio because most had six speeds bolted up to them. Stock 1.6 diffs are 4.3:1 for reference.

I went with the NB's 4.3:1 because I've stayed N/A and didn't want taller gears. If you opt for boost the popular choice is swapping in a 3.6:1 ratio ring to compensate for the added power.

In short, decide on your final drive ratio, then buy everything together to avoid any headaches. I'd recommend to clean everything up and replace all the seals "whilst you're in there", it'll give you piece of mind that you won't need to touch it again for another 100k miles. Good time to get new diff bushings too, most diffs won't have seen a rebuild during their lifetime either.

HTH bud!

Well there is a really nice deal on eBay for the axles, diff, and drive shaft from a 2004 Mazdaspeed Miata that looks very clean and its been available for a while so if timing is right I will probably pick that up. And I was planning on doing a nice restoration of it making it all nice and pretty.

[atlex]

Great page explaining lots of options.

https://www.beavismotorsport.com/gui...for-miata-mx5/

My suggestion.. 7" Torsen 2 with as awesome an FD ratio as you can live with.

[DarylSibcy]

I forgot to mention the different Torsen types, poor show

I went with an OS Giken in the end so didn’t have to think about that

[MaRcOp01o]

I forgot to mention the different Torsen types, poor show

I went with an OS Giken in the end so didn’t have to think about that

I have seen a couple Cusco diffs at not a bad price.

[DarylSibcy]

I have seen a couple Cusco diffs at not a bad price.

I considered the Cusco diff, just couldn’t find anyone who had one to share their experiences. I only put the Giken in because the Torsen was too tired to do its job.

That and if you lift a wheel for any reason a Torsen turns into an Open diff anyway, so it’s all moot

[SFL Miata]

Hey Marco your 97 already has the larger 1.8 diff and it may even have a torsen. Very easy to check by just popping off an axle and looking through the diff spline. If there is a bar across it you have an open. If you can see through it you have a torsen.

The Mazdaspeed unit will be a 3.9 final drive since those cars came with a 6 speed transmission. Not the ideal final drive for a near stock powered Miata and a 5 speed transmission.

I suggest you check your diff before spending any money. Torsen is really all you need unless you are doing some serious track duty (I.e. competing). Torsen also doesn’t wear out since it uses gears to lock and not fluid like a VLSD in the 1.6 diffs.

[MaRcOp01o]

Hey Marco your 97 already has the larger 1.8 diff and it may even have a torsen. Very easy to check by just popping off an axle and looking through the diff spline. If there is a bar across it you have an open. If you can see through it you have a torsen.

The Mazdaspeed unit will be a 3.9 final drive since those cars came with a 6 speed transmission. Not the ideal final drive for a near stock powered Miata and a 5 speed transmission.

I suggest you check your diff before spending any money. Torsen is really all you need unless you are doing some serious track duty (I.e. competing). Torsen also doesn’t wear out since it uses gears to lock and not fluid like a VLSD in the 1.6 diffs.

Hmm good point. I believe the car does have an open diff. but i will check using your method first.

[— kung fu jesus —]

Well there is a really nice deal on eBay for the axles, diff, and drive shaft from a 2004 Mazdaspeed Miata that looks very clean and its been available for a while so if timing is right I will probably pick that up. And I was planning on doing a nice restoration of it making it all nice and pretty.

The MSM diff uses different axles (maybe driveshaft too, can't remember). Those axles are not easy to find because they are specific to that model. The cone/plate LSDs of all the '03-05 miatas aren't generally regarded as being nearly as stout as the mechanical Torsen differentials. Broken/chipped friction plates are not uncommon. I've personally pulled an MSM diff from a race car that burned up and caught fire when the axles were popped out and the oil inside was exposed to more oxygen.

[MaRcOp01o]

The MSM diff uses different axles (maybe driveshaft too, can't remember). Those axles are not easy to find because they are specific to that model. The cone/plate LSDs of all the '03-05 miatas aren't generally regarded as being nearly as stout as the mechanical Torsen differentials. Broken/chipped friction plates are not uncommon. I've personally pulled an MSM diff from a race car that burned up and caught fire when the axles were popped out and the oil inside was exposed to more oxygen.

I bet that was exciting. The listing i am looking at comes with everything for the swap. But like SFL MIATA said i should take an axle out and check before doing any purchasing.

[— kung fu jesus —]

Agreed. In general, those Tochigi-Fuji differentials aren't highly-regarded. There's a reason the price is cheap.