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Old 02-27-2007, 02:32 PM   #1
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Default 3.909 Ring and Pinion - 7"

Have a 3.909 ring and pinion off an RX7. Will fit all 94-05 diffs.

dunno if any of you are looking for taller gears who have a 4.3 torsen, but here ya go.

$75 plus shipping.
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Old 02-27-2007, 03:36 PM   #2
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DOOD
I want.

edit: i'm not paying for shipping.
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Old 02-27-2007, 04:00 PM   #3
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Um......if its out of an RX7 diff, then the pinion won't fit a Miata, its far too long, the housing is very different than the Miatas. Only the ring gear will transfer. Of course, that is unless the pinion gear is out of a 1st gen RX7, then it would work as they have the same length pinion gear.
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Old 02-27-2007, 04:21 PM   #4
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so... what year brainsy?

randy's site says 79-83 had the 11:43 3.909 ratio.
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Old 02-27-2007, 05:06 PM   #5
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its from a 85 GSL...I can double check the teeth count to make sure...I'm pretty sure Randy has all the RX7 ratios wrong. should be 11 pinon teeth and 43 ring teeth, but like i said I'll double check.

Karter, it's from a short pinon nose RX7 diff. It's the exact same. infact I could bolt the pinon housing up to my carrier, but then I wouldn't have the PPF brackets.


from all the research I've done:

The 84-85 GSL is a 3.909.

The 84-85 GSL-SE is 4.08.

The 86-88 BASE, SPORT, SE and GXL is 4.10 w/manual, 3.909 with auto.
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Old 02-27-2007, 07:47 PM   #6
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The pinion will be too long for a miata, the RX7 pinion gears are not interchangable with the 7" miata

edit, missed your post scott didnt realize there were short housings that came on some rx7s
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Old 02-27-2007, 07:49 PM   #7
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Quote:
Originally Posted by akaryrye View Post
The pinion will be too long for a miata, the RX7 pinion gears are not interchangable with the 7" miata
then how do so many people run RX-7 LSD's in the 1.8 diff housings?
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Old 02-27-2007, 09:56 PM   #8
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Quote:
Originally Posted by ruger988 View Post
then how do so many people run RX-7 LSD's in the 1.8 diff housings?
You use the Miata ring and pinion with the RX-7 LSD. Simple as that.
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Old 02-27-2007, 11:35 PM   #9
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see this:



The 84-85 pinon housing is the same length as for the miata. I will measure each and show a comparison. What isn't the same is the cast for the PPF mounts for the miata. Otherwise it could bolt right up.

miata housing:



the 86-88 pinon housing is the "long" nose and will not fit:




the funny part is, the 84-85 pinon housing is the only part you can use, as the car is a solid rear axle. the 86-88 pinon housing cannot be used, as it is too long, however, you can use the carrier.
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Old 02-27-2007, 11:44 PM   #10
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Quote:
Originally Posted by ruger988 View Post
then how do so many people run RX-7 LSD's in the 1.8 diff housings?
we use miata gears and the rx7 lsd unit not the rx gears.
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Old 02-28-2007, 01:17 AM   #11
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Quote:
Originally Posted by ruger988 View Post
then how do so many people run RX-7 LSD's in the 1.8 diff housings?
setup. you can swap only the ring gears and MAYBE bearings and then setting backlash is really easy.

I'm not sure about pinion depth. T'will be a challenge.

Anyway, scottbrain, can I get a "if it dont fit, you must acquit" money-back guarantee?
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Old 02-28-2007, 01:28 AM   #12
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sorry to threadjack, but does anyone have a link to any good information on setting the backlash? It does not have to be specific but I want to understand the principle.
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Old 02-28-2007, 10:45 AM   #13
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Quote:
Originally Posted by y8s View Post
Anyway, scottbrain, can I get a "if it dont fit, you must acquit" money-back guarantee?
yes, im an ***, not a dick :gay:

Quote:
Originally Posted by akaryrye View Post
sorry to threadjack, but does anyone have a link to any good information on setting the backlash? It does not have to be specific but I want to understand the principle.
When you turn the pinion on your differential it will turn a specific amount of space before it actually contacts the the ring gear to turn your axles. If you have too little backlash the pinion is jammed into the ring gear and this will produce a lot of friction and heat and will lock up your rear axle. It will not turn freely. If you have too much backlash the pinion and ring gear will be too far apart and this will allow the gears not to mess properly and with the force of your motor will chip and destroy the teeth of the gears. This will cause excessive whining and will eventually destroy your axle again.
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Old 02-28-2007, 02:07 PM   #14
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confirmed, 11 pinion teeth, 43 gear teeth. 43 / 11 = 3.909

Matt whenever you wanna pick it up I should have it, expect for tonight as I'll be watching the Wizards & The Heat
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Old 02-28-2007, 03:28 PM   #15
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ok. Friday Donut?
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Old 02-28-2007, 03:30 PM   #16
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probably won't be there either, I close tomorrow and will be slaving away at the new place and then going out with the wifey to celebrate. just give me a call whenever, you know the numba.
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