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Old 12-22-2009, 10:39 AM   #1
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Default 6 speed and 3.9 rear end swap

im possibly getting a sweet *** deal on a 6 speed and 3.9 torsen out of an 03!

and my question is will the axles from my car directly bolt up to the 3.9 torsen out of the 03? my car currently has the 4.10 torsen!

is there anything i need to know as far as the swap goes?
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Old 12-22-2009, 10:41 AM   #2
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Direct swap, but I'd avoid the T-F diff in general, and 03 diff in particular.
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Old 12-22-2009, 10:47 AM   #3
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Quote:
Originally Posted by Ben View Post
Direct swap, but I'd avoid the T-F diff in general, and 03 diff in particular.
from what i have heard 6 speed plus 4.10 final gear = suck



i know the six speed is a direct swap, i just have to modify the neutral and reverse wiring right!
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Old 12-22-2009, 10:59 AM   #4
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Quote:
Originally Posted by WonTon View Post
from what i have heard 6 speed plus 4.10 final gear = suck



i know the six speed is a direct swap, i just have to modify the neutral and reverse wiring right!
I think it depends on what you want. I thought Sav mentioned in a thread that the fastest car at one of the tracks he races has a 6 speed with 4:10 gear.

I haven't got my 6 speed in yet so I can't give an opinion.
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Old 12-22-2009, 11:07 AM   #5
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Quote:
Originally Posted by Ben View Post
Direct swap, but I'd avoid the T-F diff in general, and 03 diff in particular.
Care to explain that one? Genuinely curious as to why...

Quote:
Originally Posted by WonTon View Post
i know the six speed is a direct swap, i just have to modify the neutral and reverse wiring right!
Yep, which is easy. And you know about keeping the engine/trans. plate and the 6-speed starter for your car.

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Originally Posted by djp0623 View Post
I think it depends on what you want. I thought Sav mentioned in a thread that the fastest car at one of the tracks he races has a 6 speed with 4:10 gear.
This is for being livable on the street, so lower RPMs at cruise is preferable.
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Old 12-22-2009, 11:13 AM   #6
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Quote:
Originally Posted by RotorNutFD3S View Post
Care to explain that one? Genuinely curious as to why...
+1 on info

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Yep, which is easy. And you know about keeping the engine/trans. plate and the 6-speed starter for your car.
ill be using the 6 speed starter right...(engine/trans plate)? im trying to remember what all we did when we assembled your car rip!


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This is for being livable on the street, so lower RPMs at cruise is preferable.
yup......4 grand in 5th gear on interstate sucks!
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Old 12-22-2009, 11:28 AM   #7
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would it be better to just go 3.6 if you are going to spend the money? Just try to get the six speed for a good deal, then buy a ring and pinion. That has been my plan. I just don't want to buy it until I have actually driven my six speed with the 4.10
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Old 12-22-2009, 11:29 AM   #8
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Originally Posted by djp0623 View Post
would it be better to just go 3.6 if you are going to spend the money? Just try to get the six speed for a good deal, then buy a ring and pinion. That has been my plan. I just don't want to buy it until I have actually driven my six speed with the 4.10
im not spending any money!!!
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Old 12-22-2009, 11:32 AM   #9
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Quote:
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ill be using the 6 speed starter right...(engine/trans plate)? im trying to remember what all we did when we assembled your car rip!
Yep, better to use the 6-speed starter than keep the 5-speed starter due to attachment differences. And it's there for the taking, so might as well.

I'm referring to the thin metal plate that goes between the engine block and transmission, also has the grounding strap on it. The dipstick also attaches to it.

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im not spending any money!!!
Can't beat a free swap.
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Old 12-22-2009, 11:36 AM   #10
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Quote:
Originally Posted by RotorNutFD3S View Post
Yep, better to use the 6-speed starter than keep the 5-speed starter due to attachment differences. And it's there for the taking, so might as well.

I'm referring to the thin metal plate that goes between the engine block and transmission, also has the grounding strap on it. The dipstick also attaches to it.



Can't beat a free swap.
ahhhh! i remember now! thats the same thing i picked up that went to your 5 speed that i thought we left off your car when we put the engine and trans together!


mmmm i love free upgrades!
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Old 12-22-2009, 11:37 AM   #11
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Almost every (or maybe every) 1.8 diff I've seen die of natural causes was an 03. Many were simply assembled wrong at the factory. I have posted pictures before.

Almost every LSD failure I've seen is a T-F, where the clutch breaks apart.

03 was the only year of the 3.909 T-F. Sounds like fail on top of fail to me.
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Old 12-22-2009, 11:58 AM   #12
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Quote:
Originally Posted by Ben View Post
Almost every (or maybe every) 1.8 diff I've seen die of natural causes was an 03. Many were simply assembled wrong at the factory. I have posted pictures before.

Almost every LSD failure I've seen is a T-F, where the clutch breaks apart.

03 was the only year of the 3.909 T-F. Sounds like fail on top of fail to me.
FWIW I have an 03 w/ LSD and I've used that torson so hard and it's survived ridiculous amounts of launches and horrible wheelhop and is still so happy. This is just my experience out of 100,000 though.
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Old 12-22-2009, 12:19 PM   #13
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im deff workin on getting the 6 speed!

moar info in regards to the 3.909 torsen diff please?
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Old 12-22-2009, 12:28 PM   #14
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You'll be fine with swapping everything over, don't worry. The 03 Torsen isn't the best of the OE options, but for what you're doing, you'll never notice the difference. Maybe down the road if you seriously get competitive in autoX or something you'll notice it's performance shortcomings, but until then.....
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Old 12-22-2009, 12:38 PM   #15
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Someone buy my awesome 3.9 assembly with no axles. I am going to a 3.6 clutch setup.
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Old 12-22-2009, 12:42 PM   #16
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Quote:
Originally Posted by Doppelgänger View Post
You'll be fine with swapping everything over, don't worry. The 03 Torsen isn't the best of the OE options, but for what you're doing, you'll never notice the difference. Maybe down the road if you seriously get competitive in autoX or something you'll notice it's performance shortcomings, but until then.....
thanks for the input mike!

if in the future i go for more power and other nonsence ill prolly do what rip did with his diff!
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Old 12-22-2009, 12:43 PM   #17
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Threads are hard to find, but if you search hard enough, you will find jems like these:
Differential going? - MX-5 Miata Forum
Something fell out of my LSD diff. What is it? - MX-5 Miata Forum

The common thread between the blown up 03 units is that they all seem to die with low miles on them, so if the particular unit you're looking at is higher mileage, it might be just fine. Kind of like the 97-00 thrust bearing failures; if it didn't pop by 40K, then it's probably not gonna (though some motors did give up the ghost around 100k)
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Old 12-22-2009, 12:45 PM   #18
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78,000 miles on this particular car.
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Old 12-22-2009, 12:57 PM   #19
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Here's a 03 5-speed unit w 20K
https://www.miataturbo.net/forum/t23630/
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Old 12-22-2009, 01:19 PM   #20
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all recorded failures have been 35k miles and below!

the unit im trying to get my hands on has almost 80k...........if there was a problem with it like the others that have been linked, wouldnt it have already failed?
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