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HAMMER DOWN 05-07-2007 06:06 PM

STi 6 speed swap in 05 GT
Just thought I share the mod I'm about to do.
The parts will be in Friday or Monday the latest. [6 speed tranaxle, rear diff, drive shaft, flywheel, pressure plate, new clutch disk and DCCD controller.

Why? My GT is 20 mos. old, 50 runs down the drag track and 68k on her. At 62k she grinds going from 3rd to 4th when you shift above 4500 rpms. Then at 67k the clutch slips on 5th gear roll-on from 55mph. Only when it's in the low 60F's or colder. If it's almost 70F or higher she don't slip. The only thing I can think of is the the clutch is on her way out, but not totally gone. I think it's the HP. & Torque . difference between colder air and the warn air. For ex. I want to 1/4 mile drag strip. When the temp. was around 80F. I was running low 15 sec. Then when it got cooler, around 55F to 60F. My times drop to low 14 sec.

Time frame, if a friend [owns his own auto repair bissness] of mine can do it reasonable. I have it done soon. If not I do it this Aug. if the tranny & clutch last that long when my work goes on two week shut down.

I'm also Email COBB. To see if I have to run a custom maps with this mod or run the 93oct. map or STi maps. But I think if I go with the STi maps I have to take my GT to stage 2. Don't know will see.


Originally Posted by NSFW (Post 4482184)
I don't disagree with merging my 6MT thread into this one, but it does kinda suck that the single most useful post in this whole thread is buried in the middle, at position 530.

And I'd like to think that 531-534 are pretty helpful too, if you don't mind my saying so.

Can we bump those to the top, or at least can we bump 530 up to the top?

With those posts buried right in the middle of this more-than-a-thousand-post-long thread, they are going to be exactly as helpful to other people as if you'd just deleted my thread completely.


Originally Posted by MiniStiGuy (Post 4484330)
I'm not sure if we can bump them to the top but here are the links for all the posts. The OP can edit his first post and add them in.

Post# 530

Originally Posted by NSFW (Post 3055604)
I typically create threads like this after the stuff gets installed, but I'm making an exception in this case because I need a place to take notes while I sort through the information that is sprinkled throughout the "6mt master swap thread" (and others) so that the next person to undertake this swap won't have to go on an easter-egg hunt to learn what they need to know.

There are two main recipes for 6MT swaps. They key difference between them is the rear diff ratio. Both use 3.9:1 front differentials, but the later transmissions have a 1.1:1 ratio on the rear output shaft, which requires a 3.54:1 rear diff.

Recipe A - 3.90 rear diff
Transmission options: 04/05 STI*, or 08/09 Spec B
Rear diff options: 04/05 STI, possibly 07-09 Legacy GT R160**
Rear axles: 07-09 Spec B (axles 28421AG03B, axle seals 806732200)
Front axles: Regular LGT***
Driveshaft: use a Spec B driveshaft, and replace the differential's input flange with the R160 flange.
(The Spec B R180 has an R160 input yoke, but is only available in 3.54:1.)

Recipe B - 3.54:1 rear diff
Transmission options: 06+ STI (I don't know what the upper bound is, but unclemat used an 08)
Rear diff options: 02-05 WRX R160, 07-09 Spec B R180*****
Rear axles: Regular LGT with R160, Spec B axles with R180.
Front axles: Regular LGT
Driveshaft: Spec B****

Note that there are two versions of the Spec B 6MT transmission and they have different final drive ratios.

* Some 04 STI transmissions need minor changes for LGT front axles - click here for more info.
** I have conflicting information about which Legacy GT R160s have which ratios.
*** 04 6MT will need new axle seals to use LGT front axles. (Part numbers here)
**** Per Z0rro, an 05-09 4EAT driveshaft can substitute for a Spec B driveshaft.
***** says the 08/09 Spec B uses a 3.9 final drive, however that apparently includes the 1.1 reduction in the transmission.

Small parts: (needed for either recipe)

Please confirm these part numbers for your particular transmission.
Most of these are just what I used for my 05 STI 6MT swap; later years may have differences.

Keep your 5MT neutral sensor switch, put it in the 6MT.
6MT shift linkage (Preferably Spec B; the Impreza shift linkage is shorter) (Is this still true for 08+ Impreza?)
6MT clutch fork - 30530AA050
6MT clutch release shaft - 30532AA020
6MT clutch slave cylinder - 30620AA172 - alternate:30620AA173
6MT clutch hose
6MT throw-out bearing
6MT rear transmission mount (same part for Spec B and Impreza)
Reverse lockout cable - 35060AG010
Downpipe support bracket - 44021FE030
R180 diff mount from the spec B - 41310AG040 (not strictly necessary, but click here for some info)
Clutch fork shaft plug (threaded cap that holds the fork shaft in) - 30550AA000 for 04-07, and 11021AA010 for 08+
Output Shaft Oil Seal (oil seal for the driveshaft interface) - 806735210 - $11.50
Clutch fork spring (spring that connects clutch fork to bell housing) - 30546AA060 - $5.20
Inner shift boot (foam/rubber, mostly for noise insulation, you can reuse the 5MT if you trim it)
If you get a DCCD diff, you'll need an aftermarket DCCD controller.

Courtesy of ShockerGT:
If you have an STI shift linkage, the shift lever will not be centered as the STI shifter rod and shifter stay are shorter than the Legacy parts. So, you'll need these:

Spec B Shifter Rod: 35041AG020
Spec B Shifter Stay: 35031AG020

Stick with 04-07 STI shift levers, as the 08+ versions are not compatible.

What you DON'T need:

Vehicle speed sensor - the LGT speed sensor is not on/in the transmission.
6MT rear transmission crossmember (same part for 5MT, just needs the 6MT mount (the rubber part))

Considerations: (which recipe is right for you?)

The Spec B 6MT has a 50/50 torque split, lacks DCCD and has an open front diff, but is less expensive
04/05 STI 6MT has a 35/65 torque split, open center diff, and DCCD
06+ STI 6MT has a 41/59 torque split, helical center diff, and DCCD
R180 rear diffs are stronger than R160 rear diffs.
The Spec B R180 uses an R160 input yoke. Not sure how much this affects strength.
Unclemat opines on differential technology.
And so does Homemade WRX.

Last but not least, the Spec B 6MT gear ratios are more evenly spaced than the USDM STI 6MT ratios, and they're a bit taller. Rallispec will install them into STI transmissions, and they call it a "high speed" gearing option. I did it mostly for the even spacing. Better mileage would be a nice side-effect if I stayed out of boost, but how likely is that?

Reference material:

Hammer Down's thread:
sti_lusts's thread: 6MT swap thread:
BDII's NES 6MT swap thread: 6MT swap thread:
An Impreza 6MT swap:
A thread with some DccdPro info:
Info about differential types:
Spec B shifter assembly:

Part sources:

Millenium Auto - (Used Subaru parts, including 6MT transmissions)
Silverline Automotive - (6MT swap packages)
Thrash - (custom driveshaft, $650ish)
Spiider - (Aftermarket DCCD controller)
SGP - (Axles, seals, clutch fork, etc)

Instructional video:
YouTube - Subaru WRC Gearbox Change

Post# 531

Originally Posted by NSFW (Post 3055605)
I'll be using recipe A, because I want a 35/65 split and an R180 rear diff.

The major parts:

* 04-05 STI 6MT (from Silverline Automotive)
* Spec B gears for 2nd-6th (aka Rallispec's "high speed" 6MT gear ratio conversion)
* New-style synchros / baulk rings
* 04/05 STI R180 (came with the transmission)
* Custom driveshaft like Hammer Down, from (ordered direct)
* 07-09 SpecB rear axles (P/N 28421AG03B), axle seals (P/N 806732200)
* Exedy twin disc clutch (from ImportImage)

The minor parts:

* 6MT rear transmission mount (from m sprank via the classifieds)
* Spec B shift linkage (from imkindofabigdeal via the classifieds)
* Shift knob (West Coast Lathewerks copolymer sphere, via NASIOC classifieds)
* Spec B downpipe support bracket (44021FE030 - or maybe fab something, we'll see)
* clutch slave cylinder
* shift fork (fork shaft 30532AA020, plug 30550AA000)
* clutch hose (received from ImportImage)
* Spiider DCCD controller (received, direct)

These figures will vary a lot, depending on whether you can / will wait for great deals to pop up in the classifieds, but here's what I'm paying:

$3500ish for the trans and diff.
$565 for the driveshaft
$700ish for the rear axles
$300ish for a used spec B shift linkage
$300ish for the DCCD controller
Plus small parts that I haven't added up.
Plus whatever you want to spend on a clutch.

I spent about $7000 total, but it would be easy to shave $3000 off of that. Upgrading to spec B gear ratios cost me about $2000 (6th gear is taller than either STI transmission, and the ratios are more evenly spaced) and my twin-disc clutch was about $2000.

Someone said they did it for $3000 or so, partly due to a great deal on a transmission and diff. I tried looking for a great deal, but ran out of patience. :)

Post# 532

Originally Posted by NSFW (Post 3055606)
So the transmission is built and probably on a truck by now... Jodie at Rallispec was kind enough to snap a few pictures before putting it back together, including these three...

Post# 533

Originally Posted by NSFW (Post 3055607)
Start by removing these, and the front axles too:

So you're left with this:

But wait... what's wrong with this picture?

Tune in next week, when we install the shaft that the clutch fork is supposed to be sitting on, and continue where we left off... The R180 rear diff, Spec B axles, and Exedy Twin clutch are all installed, but there's nothing more we can do until that rod gets here. :spin:

Post# 534

Originally Posted by NSFW (Post 3055608)
Almost too pretty to cover up:

New (OK, used) transmission in the foreground, old one in the background:

Driveshaft comparison:

And of course the driveshaft plugs into this:

wukindada 05-07-2007 06:22 PM

I'll be interested to see what the total cost of this is going to be.......

Best of luck

unclemat 05-07-2007 06:26 PM

Thumbs up for the project


Brady 05-07-2007 07:42 PM

No need for custom maps. You'll be running the same engine, only bolted to a new transmission. There is not Transmission Control Unit. Also, a WRX STI map will not work with your Legacy GT ECU. You don't need to run Stage 2 for an STI tranny, but there also isn't any reason not to so long as you have the appropriate exhaust hardware.

AWDxBOOST 05-07-2007 08:29 PM

the map will not matter at all if all you change is the tranny

edkwon 05-07-2007 09:50 PM


Originally Posted by Brady (Post 1151775)
No need for custom maps. You'll be running the same engine, only bolted to a new transmission. There is not Transmission Control Unit. Also, a WRX STI map will not work with your Legacy GT ECU. You don't need to run Stage 2 for an STI tranny, but there also isn't any reason not to so long as you have the appropriate exhaust hardware.

aww let him try to run the Sti maps on his car, he'll either get them to work or much hilarity may ensue.

HAMMER DOWN 05-07-2007 10:39 PM

The reason I was wondering about the maps, was I notice the AP stage 1 93 oct. map was only letting so much boost per. gear. these #'s are not exact. Just an example. 1 gear 5 psi : 2 gear 8 psi : 3 gear 11 psi : 4 gear 13 psi : 5 gear 15.5 psi.

After reading your replys. My thoughts, the ECU is connected to your tranny at the speed sensor. The only way the ECU can have a max psi per gear. No matter what manual tranny is in the car. The ECU must use the motors rpms, TPS other sensors plus the cars mph to calculate max psi per. gear. If this is the case. You people are right. I can run AP's GT maps.

Thanks, Mike

FX35B4 05-08-2007 07:52 AM

You can do this after swap.

solbergfan 05-08-2007 07:54 AM

Don't forget to make the DCCD work properly there are G-sensors installed on the STi's. I think there are 2??

FoxHound 05-08-2007 11:28 AM

thats awesome... i have been thinking of doing the same...let us know how it goes

HAMMER DOWN 05-08-2007 04:38 PM


Originally Posted by solbergfan (Post 1152541)
Don't forget to make the DCCD work properly there are G-sensors installed on the STi's. I think there are 2??

If there is. I hope they are part of the DCCD control box. But question? If the DCCD is Driver Controlled. Why would it have G- sensors? Sounds like they would be part of a computer controlled. VDC Vehicle Dynamics Control (VDC) or a TCS Traction Control System (TCS) . And far has I know 05 STI's didn't have VDC & TCS.

I just checked the 07 STi, no VDC & TCS.

So thanks I'll look in to it more . When I get my parts.


AWDxBOOST 05-08-2007 04:41 PM

i think it has to do with the auto function

HAMMER DOWN 05-08-2007 04:59 PM


Originally Posted by FX35B4 (Post 1152535)

That's nice. :) But the price. :eek: :mad:

The $$$$$$$ I got in my parts,:eek: . That Sequential shifter would be big drop in the bucket, but drop none the less.

HAMMER DOWN 05-08-2007 05:11 PM


Originally Posted by AWDxBOOST (Post 1153644)
i think it has to do with the auto function

I found this. And I'll keep looking. I hope everything I need is in the DCCD control box.

Symmetrical All-Wheel Drive (AWD) Driver Controlled Center Differential (DCCD) All-Wheel Drive: Exclusive to WRX STI models, Driver Controlled Center Differential (DCCD) All-Wheel Drive, featuring both manual and automatic modes, uses an electronically managed multiplate transfer clutch and a mechanical limited-slip differential in conjunction with a planetary gear-type center differential to control power distribution between the front and rear wheels. Normally, DCCD splits power 41% front and 59% rear. Sensors monitor parameters such as wheel slippage, steering angle, throttle position and braking to help determine torque distribution and direct it to the wheels with optimum traction. DCCD also features a helical-type limited-slip front differential and a Torsen® limited-slip rear differential.

rao 05-08-2007 05:14 PM

How are you going to handle the rear half-shafts?

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