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Author Topic: Any OEM Torsen LSD legal for a '99?
Viet-Tam Luu
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Region: San Francisco Region
Car #: 14
Year : 1999
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My '99 came with an open diff. I've read the rules and searched the forums (found a related thread) and am still a bit uncertain as to what exactly is legal.

The relevant rules state:
quote:
a. Transmission and final drive ratios must remain stock for the year of car. 1999-up cars shall only use the 5 speed transmission and the 4.3 differential ratio. All cars may use the stock unmodified OEM open differential or one of the approved alternates listed below.
c. 1994 and newer cars may use the stock Torsen limited slip differential.

Okay, so what's obviously legal in my '99 are either of the diffs that it could have come with from the factory.

What I'm not clear about is, is it legal to use an LSD from, say, a '94 Miata in the '99? I believe Mazda went through about 3 different LSD designs between '94 and '99. The rules only say "the stock Torsen LSD"; however "the" is a bit unclear because it could mean any one of those three different designs. The rules don't say "the stock Torsen LSD for the model year of the car" so it could be interpreted as meaning any stock Torsen LSD... couldn't it?

I'm asking because I've managed to purchase, at a pretty good price, a new '94 LSD. I was planning on swapping it into my '99 street car, then taking the LSD from the street car and swapping it into the '99 SM. Obviously that's a bit of a PITA; could I legally just put the '94 LSD into my '99 SM (reusing the latter's ring gears, diff casing, etc.)?

On a related note, is there any advantage in using one Torsen LSD model over the other? If the '99 is "better" than the '94 I may do the 2-car swap anyway.

[ 09-17-2007, 09:21 AM: Message edited by: Viet-Tam Luu ]

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Viet-Tam Luu (a.k.a. "Tam")
SFR-SCCA #14 ITS
Director, SCCA San Francisco Region

Jfornachon Verified Driver
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From what I understand you can use any torsen on the 99+ as long as you use the proper 4.3 ratio.

If I remember right the torsen 1 (which was in the na's) was updated and now the torsen 2 is installed into the na's as a replacement. Don't quote me on that though. I have been doing a lot of readiing lately.

If you do the swap the way that you stated above then you should be good to go. You would not have to swap the grears either. You wont even have to wory about getting the back lash correct.

Havw a great day,
Jared

Mike C Verified Driver Made Donation to Website
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The 94-97 cars DO NOT have the right gear ratio (4.1). You need to run a 4.3 in the '99.

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Mike Collins
MEATHEAD Racing
http://www.SHEETZ.com
The MEATHEAD Racing 2010 Calendar is up!!!!
www.MEATHEADRacing.com
SMAC Member
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ALL OPINIONS ON RULES OR SPECIFICATIONS ARE JUST THAT, MY OPINIONS!

Viet-Tam Luu
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Mike, wouldn't the gear ratio be determined by the ring gear and the driveshaft gear (or whatever that's called)? As I said I was planning on just swapping the "pumpkin"--just the diff part--but reusing the '99 ring gear and everything else. That should leave the 4.3 ratio.

Assuming of course the '94 pumpkin will bolt up to the '99 ring gear.

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Viet-Tam Luu (a.k.a. "Tam")
SFR-SCCA #14 ITS
Director, SCCA San Francisco Region

Mike C Verified Driver Made Donation to Website
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Pumpkins are the same.

--------------------
Mike Collins
MEATHEAD Racing
http://www.SHEETZ.com
The MEATHEAD Racing 2010 Calendar is up!!!!
www.MEATHEADRacing.com
SMAC Member
WDCR-SCCA SM Drivers Rep.
ALL OPINIONS ON RULES OR SPECIFICATIONS ARE JUST THAT, MY OPINIONS!

Viet-Tam Luu
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Thanks Mike. I take it you mean that the pumpkin-to-ring-gear bolt patterns are the same. Looks like I'm all set.

As for the second part of my question: is one torsen LSD better than the other ('94 vs. '99, for example)?

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Viet-Tam Luu (a.k.a. "Tam")
SFR-SCCA #14 ITS
Director, SCCA San Francisco Region

Dave Morris Verified Driver Made Donation to Website
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Isn't it uncanny the information in his head?

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Dave Morris

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99 better than 94.

--------------------
Mike Collins
MEATHEAD Racing
http://www.SHEETZ.com
The MEATHEAD Racing 2010 Calendar is up!!!!
www.MEATHEADRacing.com
SMAC Member
WDCR-SCCA SM Drivers Rep.
ALL OPINIONS ON RULES OR SPECIFICATIONS ARE JUST THAT, MY OPINIONS!

Stitches
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Region: Cal Club
Year : 1999
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How do you tell if a '99 has a LSD? I am looking at one today to buy and I want to know if it has one when I take it to have it inspected.

--------------------
Steve
1999 Track Day Miata

Viet-Tam Luu
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Miata.net has this, but it doesn't pertain to '99s: http://www.miata.net/garage/diffguide/index.html

This may also be useful: http://www.geocities.com/MotorCity/5361/99.html

Also see this thread on Miata.net forums: http://forum.miata.net/vb/showthread.php?t=158251
And search to find many similar threads.

If the '99 has the Leather Package (tan leather seats, tan top, Bose, Nardi, etc.) it has a LSD. That's the easiest case where you can spot the LSD by looking at the outside of the car.

Also, if the car came equipped with Bilstein shocks, it has a LSD.

Finally, if the car came with the Popular Equipment Package (power steering, alloy wheels, Nardi, power mirrors, power antenna, cruise control) it has a LSD.

Both diffs use the same outer diff housing so it's impossible to tell from the outside. I hear if you open the diff fill (drain?) plug, you can look inside and see the diff. The open diff looks like this.

You should be able to tell the diffs apart (differentiate? [Smile] ) with an "enthusiastic" test drive. Keep in mind the torsen will still exhibit some inside wheel spin if the rear wheel is off the ground or just about.

The real way to know for sure, short of cracking open the diff housing, is to call Mazda with the VIN and they can tell you what package and options the car came equipped with.

--------------------
Viet-Tam Luu (a.k.a. "Tam")
SFR-SCCA #14 ITS
Director, SCCA San Francisco Region

Stitches
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I called the phone number for mazda on the website today and after about 15 minutes on hold they gave me everything I ever wanted to know about what my car came with by giving them the vin. I am pretty happy with the results. I'll spend 15 minutes on the phone before I take apart the diff any day.

--------------------
Steve
1999 Track Day Miata

Viet-Tam Luu
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quote:
Originally posted by Stitches:
I'll spend 15 minutes on the phone before I take apart the diff any day.

Amen to that! [Big Grin]

Speaking of which I spent four fun-filled hours swapping the Type 1 torsen into my '99 street car last night. [Smash]

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Viet-Tam Luu (a.k.a. "Tam")
SFR-SCCA #14 ITS
Director, SCCA San Francisco Region

jigou Verified Driver
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...assuming a previous owner didn't swap anything ever....

Jarrod

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Viet-Tam Luu
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Year : 1999
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quote:
Originally posted by jigou:
...assuming a previous owner didn't swap anything ever....

True, but whether or not you can trust them is psychological/sociological issue, not a technical one. [Big Grin]

--------------------
Viet-Tam Luu (a.k.a. "Tam")
SFR-SCCA #14 ITS
Director, SCCA San Francisco Region

   

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