OK guys, looking for an affordable Torsen unit for my SE. Would prefer the higer end unit, but the oem type will suffice . . . any advise?

 

Mazdatrix sells one for, sit down, $770.45.

Perhaps you can pilfer one off a Miata?

Will they fit?

 

I heard the oem unit for the third gen bolts in w/ a bit of shimming. Anyone?

 

The Miata Torsen supposedly bolts in with a bit of trimming.

 

The '94-up Miata pumpkin should be a direct swap into an '84-85 rear. The difference is that '84-85 had larger axles... and no you can't put '84-85 axles in an earlier rear because *everything* is different... axles/bearings/backing plates.

www.solomiata.com has a wealth of info on Miatas in particular and Mazdas in general. It's a must-read whether you're into Miatas, RX-7s, B-series trucks, or even 323/Escorts.

 

Thanks guys, keep it comin'

 

Did all 94+ Miatas have Torsens? I'm gonna start lookin for one someone wrapped around a pole, but didn't harm the rear.

What's the rear gear ratio like?

Can I put the 4.44 ring/pinion off the B2000 into the Miata pumpkin?

Do I NEED to find a 4WD B2000 or will the ring/pinion from the rear differential work as well?

 

The answers you seek can all be found at www.solomiata.com but in a nutshell: No, 3.9/4.1 or so, yes, and yes you need the front diff as the rear diff was a different size.

I'd rather have the 4.778 Kia gears myself... instead of $500+ for 4.875 gears. They'll be perfect for my Edelbrock'd big half-bridge 12A... muhuhahaha

 

4.778 Seems a bit too low for me. This'll be a street driven car with some auto-X, most likely...

 

4.77 rear gears with an -SE trans should put it pretty close to stock cruising RPM's in 5th....

 

Cool beans. And the SE tranny will bolt into my GSL with no problem or will I need to get mounts and such?

 

It *should* bolt in, my -SE and my GS trannies looked the same externally. Only difference really (that I know of) is a taller 5th gear ratio. Perfect for those stump pulling gearsets

 

Huh?

Also, dont the GSL-SE's have a little hole in the side of the tranny to vent the magic clutch dust?

 

Sigh, stump pulling= low gears

 

Going from a 3.90 to 4.78 is a 25% increase in driveshaft speed.... I don't really think a -SE trans will have a 25% taller 5th... I think a 12A 5ths is something like .817 so you'd need a .665 or something 5th to keep top gear the same...

Basically imagine driving around in a gear between 3rd and 4th, as your top gear. (I wouldn't mind ) You *could* offset the gear with taller tires, but you'd be doing an awful lot of work to wind up with no difference.

Just think, people used to put 4.56 or steeper gears in their musclecars, and they didn't have overdrive on their 4-speeds... and a 455 Olds is a lot less rev-friendly than a 12A!

 

peejay, what is the scoop on Kia gears? This is the second time I've seen a reference to them as a possible cheap alternative for a posi and steep gears. Is there a site on this or is it personal experience?

 

Ah. I see. I've never used a car to pull a stump. I usually wait till it dries out and soak it in kerosine or gas and toss in a match. Or drill the center out and drop in M80's.

****... Any cars with compatible transmissions that I could just swap 5th out to a ratio close to that? Trash the existing 4th, move the 5th to where 4th was, and put new gears on where 5th was.

I was planning on rebuilding the tranny anyhow. New synchros, bearings, and seals. I had bearing noise that disapeared once and the time I changed the tranny oil, I noticed some shinies in the old oil.

 

Kickin' this up so someone can clear up the real story on Kia posi's and Mazda rears. Pele, if you're that deep into modifying, cad your gear requirements and contact Martin Gear & Sprocket at 3106 Sprocket Dr., Arlington, TX 76015 and see if they can cut it for you. I use to deliver and pickup there as a UPS driver before I left the Evil Empire, and they do it all. The place is huge with a separate building housing their design boys. If it's not already on their shelves, they can make it. They did two giant gears for the local Six Flags park that were most impressive. They also ship UPS daily.

 

I'm telling you, go to www.solomiata.com !!! There is a ton of swap and technical info there, not just for Miatas but also RX-7s and pickups, because Mazda is a good corporation and they use only one or two designs, instead of re-inventing the wheel (or trans, or diff ) when they make a new vehicle.

The Kia diff is an open, not a limited-slip (Posi's are only found in Chevys, and only little boys have bow ties! ). Basically you just grab the pumpkin and get the gears out of it and put them into your existing rear. A '94-up Miata pumpkin will physically work in a '84-85 rear except you have to do some clearancing, and some (not all) '94-up Miatas came with Torsens.

I wouldn't worry about making 5th gear taller, unless you have a 13B. I can pull 5th gear from any speed but it doesn't *really* get moving until after 4k, at which point I'm going 80 and the wind resistance is kinda high... and 1st gear is pretty tall too with the 3.90 gears... FWIW you can't "move" 4th gear either, as 4th gear isn't a gear, it just connects the input shaft directly to the output shaft (if you don't believe me I have my spare tranny apart, I'll take pics if you'd like)

- PJ (And just *why* do I have the spare trans apart? Hmmm....)

 

I appreciate all the response guys!!!! Lemme tell you how it started. . . What sounded like a rear bearing noise (but not wheel bearing, they were replaced) came and went and came and went. I would hear it under the load of deceleration---braking, or just coasting. I t went from happening only during left hand turns during deceleration to rights and, again, on and off. Eventually I gave up my neurotic need to find the problem and just drove her. One morning after an exceptionally spirited night run in the twisties(where she made no noise) i snicked her into first and within ten feet I heard what sounded like a knocking coming from the rear, similar to what I heard on my buddy's 12A that had a 'blown rear' but not as severe. to add to the weirdness, as I drove S l o w l y for a short distance to get the car to where I could work on it, the noise sounded like it got worse over bumps, like something was bouncing up into the gears. SO. . . I have a spare 3.9 rear and was told it would swap w/ my se 4.1, but it was a pre 83 diff so after the trial of my first rear swap (on my back), I found the axles would not slide in! Inspection of my case and the pineapple, without breaking it down, showed nothing! I expected to find a cracked race or carrier bearing floating around but found ****. And yes my universals are good. Hep me!

 

at Waterford Hills Road Racing track, 4.88 is the highest gear I hear recommended, and this is a REALLY tight track too.

 

$500??? MazdaComp sells the 4.88 (aka 4.875) gears for $250 brand new. It's a competition part, so no membership is required. Just last month I picked up a used one (2K miles) for $110 shipped to my door. 4.44 gears are not competition only parts, so those require a membership, or you pay the high retail price from Mazdatrix. And 5.12 gears are inherently weak(er) due to the tooth count/size to get that ratio.

 

Have a look at the torsen unit from Guru, I love the one in my car.

www.gurumotorsports.com