Subaru STI 6MT Teardown - Not a How-To

[joebush44]

After not finding much of any type of documentation (aside from the FSM) on tearing down the STI 6 speed transmission, I decided to throw something together as a reference for anyone else looking. After shredding 2nd gear in my transmission I've been motivated to trying to get the gear stacks out of the transmission myself, mainly to save on labor costs on the rebuild. This is not a fully inclusive how-to, but covers everything involved in removing the case and gear stacks. Hopefully it will be useful to someone!

I didn't document anything having to do with removing the transmission from the vehicle - it would be my assumption if you're looking to tackle this yourself, you're mechanically savvy enough to have gotten that far...

I didn't document my steps on removing the tail housing of the transmission, but IAG's instructions for transfer gear installation is a great reference (first 4 pages)...
https://www.iagperformance.com/v/vsp...-1000-1010.pdf

That leads me to this point. The trans is on the table and the tail housing and output shaft have been removed...

Note that this specific transmission is from an '07 USDM STI and should be similar to 08+ USDM STI. 04-06 are slightly different in that they still utilized an oil pump.

I set the case on a couple of 2x4's so there is clearance for the input shaft underneath (it protrudes from the transmission bellhousing about an inch).


Disconnect the diff electrical plug


Now the diff will just slide right off of the pinion shaft. There are 4 of these clamshell bearings that go on the snout of the pinion shaft, between the diff and the pinion shaft


You should now see this view (pinion shaft with diff removed pictured top (sleeping doggo optional))


Side view


Remove this roll pin


Roll pin removed


Remove snap ring and washer


cont...

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[joebush44]

Pull up to slide the spring out. Careful because it will snap shut and could pinch your finger!




Next, on the side of the case remove this bolt, spring and ball (top center of picture, partially backed out)



With that removed, these will both pop out together



You should be left with a view similar to this



Remove all of the torx (size 40) bolts holding the oil pump block plate onto the housing. (Note: this transmission is out of a late '07 STi so it no longer has the trans oil pump. This section will be slightly different for 04-06 STi transmissions. Please refer to the FSM for any missing steps here)


Pump block plate removed


cont...

[joebush44]

Remove the spacer and snap ring from the main gear stack



Next remove the 3 spacers from the pinion shaft


Current view with snap ring and spacers removed


Remove these two bolts from the side of the case



And this one (center of pic and partially backed out)



Remove all of the bolts holding the case on



cont...

[joebush44]

Don't forget the 3 nuts that are under the oil pan


With a little persuasion to loosen the RTV, the case should easily slide right off (do not force it)


Lots of spin-a-ma-things going on in here


Push the center shift fork up to shift the trans into 4th gear


This allows room to remove the reverse idler holder



Next remove the 3 plugs and springs that hold the shift fork shafts in




And remove this one that holds the reverse gear shaft in



cont...

[joebush44]

At this point you are ready to pull the gear stacks out. They have to come out with the shift forks and reverse gear all simultaneously. An extra hand would be very helpful. I ended up laying the trans on it's side so I could pull everything out at the same time by myself.

Gear stacks out



The shift forks will just come right off the stacks


What you're left with


And there you have it - gear stacks are out. My plan is to take the gear stacks to my favorite Subaru performance shop so they can swap the gears out. My understanding is that you need to setup a jig of sorts in a press to be able to get the stacks disassembled - I'll leave that for the pros. Side note: 1st and 2nd drive gears are part of the input shaft, so in my case I'll be needing a new input shaft in order to replace the shredded 2nd gear (as well as a new 2nd gear driven gear)


Reassemble in reverse order

Hopefully this is somewhat helpful. If you have to go into the trans further than this to get to the front diff, you're on your own unfortunately. Feel free to post any questions/comments!

[Unabomber]

I like this as a way for some to save a good chunk of money. Most shops will charge $700ish just to remove and replace the trans. The light teardown show here isn't rocket science either and is couple hundo for sure.

The gears themselves....yeah....that's professional only as most of us don't have 6 foot torque wrench!

[joebush44]

Exactly! $700-1000 for just labor hours. Most of the cost with a transmission repair, at least for the 6mt, is labor. Parts aren't very expensive. As long as you can find a shop who's willing to do the work despite you tearing the trans down on your own, this is the way to go.

I can pretty much work on anything mechanical, but I've always been scared to crack the transmission open. This wasn't all that bad, honestly. Although, assembly could be a different story (should be manageable with the FSM to reference). To be continued...

[ERMAHGERD SURBARRUR]

Bravo on documenting this in such a straightforward way.
I recently picked up a 6 speed swap and have been having trouble finding a local shop that will teardown/ inspect and rebuild. How much do the gear stacks weigh approximately? It would be a lot easier to ship this way to somewhere reputable for synchros, or at least get it in my car by myself!
Turn in concepts is about 3 hours away from me in NE Ohio, and they quoted me $300 just to teardown/inspect; this tutorial should definitely make things easier on the wallet! Now I'll feel better about picking up an sti cluster to get the dccd experience xD
Thanks!

[joebush44]

They probably weigh 50lbs maybe,give or take? Personally I don't know how comfortable I would be boxing them up and shipping them though. I've had too many mishaps over they years shipping/receiving things so I'd avoid shipping entirely if at all possible. Secondly the input shaft is about 3' long with the main gearset attached to it which would make shipping a bit of a challenge due to the weight/shape. 3hrs isn't a bad drive IMO. Good luck!

[atomicjoe23]

JoeBush44,

Thanks for posting this information; we need to convert a '17 STi transmission to FWD for a mid-engine application and this will be helpful for sure.

Thanks again!!!

[ckata22]

Out of curiosity, what symptoms presented when in second gear? I can imagine, or just ask you. I'm just wondering how you knew what the problem was and how you broke it, if you know.

[joebush44]

Originally Posted by ckata22

Out of curiosity, what symptoms presented when in second gear? I can imagine, or just ask you. I'm just wondering how you knew what the problem was and how you broke it, if you know.

I flat foot shifted from 1 to 2 and when it went into second it made a noise like there were rocks in the transmission and then wouldn't go anymore lol. All the other gears worked still, but in second it sounded like death (metal chewing metal)

[gustavo1004]

My 4 gear on my 5 speed doesn't work] after I did the clutch