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#1
Qyxz

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I've been reading the diff spotters guide on miata.net on how to ID a diff from looking at the axle holes but the way the pictures are labeled is confusing me. Can someone help me confirm the following?

 

This picture is a 4.3 open diff: https://www.miata.ne...iffguide/07.jpg

 

And this picture is a 4.3 Torsen diff: https://www.miata.ne...sen-closeup.jpg

 

Thanks in advance. 


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#2
Jim Drago

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I've been reading the diff spotters guide on miata.net on how to ID a diff from looking at the axle holes but the way the pictures are labeled is confusing me. Can someone help me confirm the following?

 

This picture is a 4.3 open diff: https://www.miata.ne...iffguide/07.jpg

 

And this picture is a 4.3 Torsen diff: https://www.miata.ne...sen-closeup.jpg

 

Thanks in advance. 

Well that is correct on torsen vs non torsen.. But No way to tell what ratio it is without counting teeth... 10:43 is 4:30, 11:43 is a 3:90. 


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#3
Qyxz

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Well that is correct on torsen vs non torsen.. But No way to tell what ratio it is without counting teeth... 10:43 is 4:30, 11:43 is a 3:90. 

 

Could I just spin the input plate and count the rotations of the axle?  1 driveshaft rotation to 4.3 axle rotations, right?


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#4
chris haldeman

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You have it backwards. 4.3 input rotations to 1 axle rotaion
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#5
davew

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Well that is correct on torsen vs non torsen.. But No way to tell what ratio it is without counting teeth... 10:43 is 4:30, 11:43 is a 3:90. 

 

And a 10:41 is a 4.10 ratio

 

3.9 vs 4.1 vs 4.3, you better be accurate with your revolution counting


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#6
Marc Cefalo

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mike, to be 100% sure the center section has to come out of the aluminum housing.  ring great teeth and the pinion gear teeth must be counted.  simply looking at the type of hole when the cv axles are out, doesn't cut it.  it may have been changed in a previous life.

 

Is this Nikki Coello's old black car that your asking about???


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#7
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Do all 3.9's have an 11 tooth pinion ?


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#8
Ron Alan

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Do all 3.9's have an 11 tooth pinion ?

I would say yes...at least in Mazda?


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#9
BorisB

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I

 

I would say yes...at least in Mazda?

Yeah, only talking about our little cars.

Just curious if all 3.9's were 11-43 or was there a 10-39 setup ?


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#10
Qyxz

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Well that is correct on torsen vs non torsen.. But No way to tell what ratio it is without counting teeth... 10:43 is 4:30, 11:43 is a 3:90. 

And a 10:41 is a 4.10 ratio

 

3.9 vs 4.1 vs 4.3, you better be accurate with your revolution counting

mike, to be 100% sure the center section has to come out of the aluminum housing.  ring great teeth and the pinion gear teeth must be counted.  simply looking at the type of hole when the cv axles are out, doesn't cut it.  it may have been changed in a previous life.

 

Is this Nikki Coello's old black car that your asking about???

 

 

Thanks guys I will crack it open and give it a count.  This is for a new diff that I am picking up.  My car currently is confirmed to have the 3.9. 

 

Marc - I am not sure if Nikki Coello is a previous owner.  This car came from the midwest.  There's a few names in the log book but I don't remember them off the top of my head other than the last owner.  I just ran it this weekend at July Sprints @ WGI - I was the guy parked next to Mr. Fetch. The car was in your shop earlier this year to do a non-restrictor dyno and setup.  :)


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#11
SaulSpeedwell

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Do all 3.9's have an 11 tooth pinion ?

 

Yes.


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#12
SaulSpeedwell

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I've been reading the diff spotters guide on miata.net on how to ID a diff from looking at the axle holes but the way the pictures are labeled is confusing me. Can someone help me confirm the following?

 

This picture is a 4.3 open diff: https://www.miata.ne...iffguide/07.jpg

 

And this picture is a 4.3 Torsen diff: https://www.miata.ne...sen-closeup.jpg

 

Thanks in advance. 

 

96-97 T-2s, and *possibly* some JDM T-2s, will not have the characteristic washer look to them.


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#13
Ron Alan

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^^^ Straight hole through will be a T1 or early T2 as Saul points out!


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#14
SaulSpeedwell

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These videos are reposts from other threads, but the version on left will have a 4020 prefix on the serial number.  Version on the right is more common, will have 4030 prefix.  Both are legal for any 1.8L Spec Miata. 

 

 

I fail to mention in the above video that the "coating" is from the factory and is nothing nefarious.  Later factory Torsens have no coating at all, as shown in second video.

 


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