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Old 05-09-2017, 07:53 AM   #1
RicersWetDream
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Join Date: Apr 2010
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Location: Marshall, MI
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2009 WRX
2014 Forester XT

Default Swapping 15+ STI Six Speed into 08-14 WRX

So I pulled the trigger on swapping a six speed into my 09 WRX and I wanted to get as new of a transmission as possible (why put an old dirty one in??). I found a very clean six speed with linkage, shifter, and r180 out of a wrecked 2015 STI so I pulled the trigger and bought it.





Now, I already have 90% of the work done and the trans is in the car so I'm posting this more for information. I couldn't find a thread from anybody that had swapped a six speed from the new (15+) body style STI's into the 08-14 WRX so I had a few concerns going in.... Turns out it's nearly a direct swap.

Gear Ratios - Same as 08-14 STI's but here they are again:
1 - 3.636
2 - 2.235
3 - 1.521
4 - 1.137
5 - 0.971
6 - 0.756
r - 3.545
FD - 3.90


Trans itself bolts right up like any other six speed swap, no issues clearing the turbo on the way in.

My transmission came with a crossmember so I used it and it bolts right up. I was able to swap my Kartboy bushings from my existing crossmember. What I'm not 100% sure on is if there is an elevation difference in the WRX/STI crossmember that is made up for in the transmission mount, so I guess I can't confirm that the WRX crossmember will work, but I'm guessing it will, you'll just need to use the right transmission mount.... See below.

Tranmission Mount - I went aftermarket and got the Perrin mount, which includes a spacer if you're using it on a five speed (hence why I think you need a six speed trans mount). What I don't know is where the elevation difference lies... The mount for the 5 MT is about 1/2" taller than the 6MT, is that because the crossmember on the 5MT sits slightly lower than the 6MT crossmember, or because the 5MT transmission sits slightly higher than the 6MT transmission? Since I used the 6MT crossmember and the Perrin mount I didn't have a problem, but it's still a question I have. Somebody chime in here.

My main concern - linkage length is the same (I want to say it was about 41" from face of bell housing to center of shifter), so I was able to utilize the 2015 STI linkage. Bolts right into the rear shifter stay and fits perfect in the shifter boot area. All bolts for the rubber boot that seals the shifter line up with no issues.



Shifter - This one's obvious but you'll need a six speed shifter and knob. Duh

Front Shifter Bushings - If you procure a shifter linkage with the trans like I did, the OEM bushings obviously are fine. You cannot swap the bushings from the five speed linkage to the six speed. I was hoping to swap my five speed Kartboy front bushings but they are a different size. You'll need to purchase front bushings specific for a six speed linkage

Rear Shifter Stay - I have a group-N from my WRX five speed linkage and it fits just fine with the six speed

Clutch & Fly - You'll need to swap to an STI clutch, flywheel, and fork do to the push-vs pull style clutch. The six speed pressure plate has 9 bolts holding it on versus 6 on the five speed so you'll need three more bolts. You'll need m8x1.25x16mm flange head grade 10.9. No washers needed, that's why you get flange head

You can see the three holes below



Clutch inspection cover - The STi clutch rubbed on this when I first fired it up and made a god awful sound. Was able to get a pry bar in there to pull it down a bit and solved the problem. I knew it would be tight because it was obvious when installing the clutch so I knew what to expect if I heard a nasty sound.

Slave - You'll obviously need an STI slave cylinder to match the new push style clutch

Slave Line - You'll need a clutch slave cylinder line for a six speed.

Down pipe mounting tab - Fits perfect, my down pipe bolted right up

Pitch stop- I have an aftermarket Kartboy from my five speed and it bolted right up

Solid 4" blocks under maxed out jack stands with the rear on the ground giving you an angle towards the front of the car lets you slide it in on the trans jack. Wheel ramps and 4x4's for a bit of safety:



Second main concern - Electrical

I was able to swap the NPS/Reverse extension harness from my five speed. It plugs right into the six speed's NPS and Reverse sensors, and also the engine-side plug reaches the mounting tab so it rests in the same position as the six speed plug did. Both NPS and Reverse switches function without issue, so they aren't any different.

I did have to cut the two wires for the DCCD off of the six speed's extension harness and re-pin them into a new sumitomo 2-pin connector for when I get around to installing a DCCDPro. At least now the wiring is ready to just be plugged into when I do it. In the mean time the trans will run open with 41/59 power split F/R







08+ WRX's do not have the speed sensor in the transmission and this is also true with the 15 STI transmission

Rear 02 Sensor extension cable from the 2015 STI plugs in correctly, and the O2 sensor is properly functioning

The little ground wire from the top of the STI bell housing bolts right up to the ground where the pitch stop mounts to the firewall

Front Axles - 09 WRX front axles snapped right in and bolted up to the hub with no length issues

Rear Axles - I've heard differing reports about 08-10 rear axles being too short due to the narrow body, but 11-14 WRX axles work just fine. I've also heard that the 08-10 axles do fit just fine..... Either way I went the aftermarket route and purchased DSS 800hp Hybrid rear axles for the 08-10 WRX with r180 swap since I'm building the car for ~500ish at the wheels

Starter - The 09 WRX starter bolts right up, BUT the starter will rub on the larger diameter STI clutch and bind up (this goes for all 08-14 WRX starters). You'll need an STI starter.

Rear Diff Mounting - Bolts right up

Driveshaft - DSS CF shaft for 08-14 STI bolted right up. The rear diff flange will need to be drilled out because DSS includes larger bolts for mounting their shaft. You could re-use your oem flange bolts, but I preferred to have the bolts match the hole size.

Trans & Rear Diff Oil - I picked up six quarts of Subaru 75w-90. Used a bit over 1 quart in the diff, and the remainder in the trans.... I tend to fill until oil really starts to run out of the fill port and let it drain off for a few minutes so I probably wasted 1/4-1/2 a quart doing that.

I believe that's it and like I said it's a pretty seamless swap in terms of parts compatibility with the new model. I don't know that I'm exactly adding anything to the community other than confirm that at least the 2015 STI trans into an 08-14 WRX is easy.

Full parts list of swap for record:

2015 STI Six Speed Transmission with OEM Linkage
2015 STI r180 Rear Differential
2015 STI Transmission Crossmember
2015 STI Rear Diff Carrier
2015 STI O2 Sensor Extension
2015 STI Clutch Fork Return Spring
2015 STI Starter Motor (Denso 2800387)
2009 WRX Trans Switch Harness Extension
ACT HD Clutch - STI
ACD Streetlight Flwheel - STI
Three more m8x1.25x16mm flange head grade 10.9 bolts
Centric Clutch Slave Cylinder for 6 Speed
Goodridge Clutch Slave Cylinder Braided Hose
Whiteline Positive Power Kit from my r160
Kartboy Postive Shift Kit from my 5 speed
Kartboy Pitch Stop (re-used existing that I had purchased for 5-speed)
Perrin Transmission Mount
Driveshaft Shop CF Driveshaft for 08-14 STI
Driveshaft Shop 2008-20012 WRX with r180 Diff 800HP Direct Fit Axles
OEM 2009 WRX Front Axles
Kartboy Six Speed Short Throw Shifter
Beatrush Duracon Six Speed Shift Knob
Subaru 75W-90 Gear oil for trans and diff

In terms of pricing - I was able to get the trans and rear diff for $3,650, all other parts since I went in head first with the axles and driveshaft put the total for the swap at about $7,300. Hoping to recoup $1,500-2k selling OEM parts as well as old ACT HD clutch and fly from the five speed

Added for posterity: This little lady loves working on and going for rides in dada's loud car

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Last edited by RicersWetDream; 06-09-2017 at 02:02 PM.
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Old 05-09-2017, 08:01 AM   #2
RicersWetDream
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2014 Forester XT

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Old 05-09-2017, 08:01 AM   #3
RicersWetDream
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2014 Forester XT

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Old 05-09-2017, 08:32 AM   #4
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Great write up, thanks for this!
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Old 05-09-2017, 11:31 AM   #5
RicersWetDream
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Updated original post - I've done more research and it does appear that 08+ WRX starters are no longer compatible with 08+ six speeds so I ordered a new one.
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Old 05-11-2017, 09:51 PM   #6
RicersWetDream
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New starter showed up today, and I got notification that my prop shaft and axles shipped so I'll have those Monday. If I have a chance to work on the car tomorrow night I'll be swapping the starter so I'll get some comparison pictures.

Also found the car my trans came from:

https://www.copart.com/lot/24493556/

Last edited by RicersWetDream; 07-19-2017 at 09:33 AM.
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Old 05-16-2017, 08:30 PM   #7
RicersWetDream
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Wrapped the IC in DEI gold, just need to slap it back on with the new throttle body hose when I get a chance. Then I just need to delete my evap system (car is gutted for a future cage, was at 2799# before the new trans went in). It'll be easier to go after the evap with rear diff out of the car.

New axles and drive shaft also showed up last night so hopefully this week/weekend I'll get it running. Should be a quick process to drill out the diff flange for the beefier hardware for the ds, then install diff/axles, drive shaft, bolt wheels back up, fill with fluids, and fire. It's a busy week at work and at home so we'll see if I can actually work on it.
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Old 05-19-2017, 12:59 PM   #8
RicersWetDream
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Got everything back together last night and filled with fluids. Everything fits and runs great! Updated first post to document the few unknowns as confirmed.
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Old 06-09-2017, 01:56 PM   #9
RicersWetDream
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Update: Have nearly 300 miles on the new trans and all is well. Still getting used to having six gears but it honestly feels faster in gear with the shorter ratios. Still getting the clutch broken in so I'm not giving it very much boost but once I get past the break in period I'll take it to the drag strip.....

The car weighed in at 2799 before the swap so I'm guessing it's around 2875 now. Hoping for 11's but the driver will be the weak link (me).
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Old 06-12-2017, 12:19 AM   #10
f22_raptor96
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This is gold, a friend of mine is looking to do the same swap but just found this thread. Thank you NASIOC!
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Old 07-19-2017, 04:39 PM   #11
subezero
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Thanks for the write up, this will be very helpful. After changing my trans fluid for my 60k service, I found some large chips of metal, so I'm beginning to save up for the 6mt. Did you try the narrow body axles in the rear or did you just go straight to the DSS axles?
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Old 07-19-2017, 05:23 PM   #12
RicersWetDream
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Went straight to DSS to future proof it a bit. Probably worth the try, just be ready for down time if they don't work, or have sti axles ready.

Last edited by RicersWetDream; 07-19-2017 at 07:03 PM.
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