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Old 06-21-2018, 06:46 AM   #1
newsti13
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Default 06 sti trans in an 04 sti

My trans is going out on my 04 sti.... im going to replace the whole transmission. Would an 06 sti trans be a direct fit in my 04 sti?
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Old 06-21-2018, 07:54 AM   #2
JarHarms
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It will "bolt in".
Working as-is, No. With extra work, yes.
To start off the Transfer Ratio is different between those two 6MTs. You would have to also change your Rdiff to avoid driveline damage. Please read up more on this before you start buying parts. Also depending on early/late 2004 STI you "could" have different front CV shaft inner connection to deal with. NPS polarity will also need to be addressed.
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Old 06-21-2018, 12:50 PM   #3
mrsaturn7085
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A few notes/corrections - JarHarms got most of it correct:

1. You will want to install the 06 STI 6MT + 06 STI R180 -or- swap the 04 STI transfer gearing into your 06 STI 6MT.

2. You will want to re-use your 04 STI front axles + stubs (there is no early/late, here... 2004 is 2004 is 2004; all 2004 STI axles are pinned stubs) and your 04 STI rear axles.

3. You will need to install non-flared 04 STI axle seals to the 6MT; R180 seals are the same between 04/06.

4. You should be aware that you will be running a 41:59 diff. on a 35:65 TCM program/mapping - this won't hurt anything... but it won't be optimized for your actual diff. characteristics. You cannot use a 2006+ (41:59) controller as it requires significantly more wiring/sensors that you don't have. If you want to pursue this, I suggest an aftermarket controller ($$) or a full body wiring conversion ($$$$$). If you aren't racing, neither will be worth the money.

5. The NPS polarity thing is a WRX to STI conversion concern. This is NOT something you will encounter and the 2004 STI and 2006 STI both use a low-side switch; the wiring is identical.

In short, it isn't a direct-fit, but it is an easy swap. It becomes a little more expensive if you have any qualms about opening the transmission up. Personally, I would source the 2006 R180 and install them as a pair - reasoning here is that if you swap transfer gearing, you need to reset your bearing preloads and this is CONSIDERABLY more labor intensive (and requires many many more specialty tools). Doing the minimum work possible, step-by-step:

1. Source 06 6MT/R180.
2. Swap axle seals on the 06 6MT for new, 2004 seals.
3. Swap the transmission and R180 in, direct-fit at this point.

You'll notice a couple things:

- Low speed maneuvers will have more stick-slip due to the more aggressive c.diff. with it's 'always-on' mechanical stage.
- Shift lever left to right movement will be reduced (internal linkage change).

...and that's it, really...

Last edited by mrsaturn7085; 06-21-2018 at 12:56 PM.
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Old 06-21-2018, 03:54 PM   #4
JarHarms
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Quote:
Originally Posted by mrsaturn7085 View Post
... -or- swap the 04 STI transfer gearing into your 06 STI 6MT....
So those can be interchanged? As in the TR drive mating within the Cdiff is the same between 2004-05 and 2006-07? I have never tried it but it makes sense that I could use a 2006 Cdiff as a replacement (with oil pump gear) for my 2005 Cdiff.


Quote:
Originally Posted by mrsaturn7085 View Post
...5. The NPS polarity thing is a WRX to STI conversion concern. This is NOT something you will encounter and the 2004 STI and 2006 STI both use a low-side switch; the wiring is identical...
Hmm. I was pretty sure the 2004 STI used 32008AA091 (normally open) and the 2005-07 STI used 32008AA160 (normally closed). Either way it is pretty easy to correct any mismatch by swapping sensors.
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Old 06-21-2018, 06:13 PM   #5
mrsaturn7085
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Quote:
Originally Posted by JarHarms View Post
So those can be interchanged? As in the TR drive mating within the Cdiff is the same between 2004-05 and 2006-07? I have never tried it but it makes sense that I could use a 2006 Cdiff as a replacement (with oil pump gear) for my 2005 Cdiff.

Hmm. I was pretty sure the 2004 STI used 32008AA091 (normally open) and the 2005-07 STI used 32008AA160 (normally closed). Either way it is pretty easy to correct any mismatch by swapping sensors.
Valid points - regarding the transfer gearing, I am 99% sure the splines are the same and I know 100% the split bearings are located at the exact same distances... but worth verifying when you take it all apart.

You're correct about the part numbers - I was unaware of this issue but good to know! This is different from the 5MT 4-pin vs. 6MT 6-pin issue I was thinking of!
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Old 06-21-2018, 09:39 PM   #6
JarHarms
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Shoot. I was hoping you would say that you have done that or had seen it done successfully.
Awhile back I spent time comparing 2005 to 2006 STI part numbers of all the Cdiffs, TR gears, housings, bearings, and related parts. Everything matches up but of course the Cdiff and TR shaft part numbers fr obvious reasons. I did not go as far as sourcing some used 2006 version parts to compare to.
One day I might invest cash into checking this out. Gaining the 2007 Cdiff and retaining my 1:1 TR would be a nice option.

I tried to compile a bunch of transmission related sensor info (incl NPS) into a useful thread awhile back.
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Old 06-22-2018, 02:41 AM   #7
mrsaturn7085
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I've rebuilt the early and later diffs. and held the 1.0 and 1.1 sets in my hands... but never at the same time. Still, I'm entirely confident it would work. I see no reason it wouldn't as the transfer gearing only affects the prop. shaft speed in the end.
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Old 07-14-2018, 03:32 AM   #8
matz73z
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Iím curious where this went. Iím in the middle of a swap to STi trans and diff and 5x114.5 hubs. The kit I got ended up being from two different vehicles (not advertised). The JDM trans and diff are early V8, but the hubs are later V8. The splines on the rear diff are not mating up to the axles provided. The axles slip into the hubs, so Iím assuming theyíre the later V8 axles.
My question and reason for asking here is to see if you ran into axle compatibility issues between the 06 diff and 04 hubs. Itís the opposite direction of my issue, but should result in the same mismatch issue.
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