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6MT Master Swap Thread


HAMMER DOWN

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Lists looks good, need to use the OEM natural safety switch,[NSS] out of the 5MT, for the cruise control to work. Shifting boot, inner & outer. Unless you going to cut them down a little to fit the 6MT's shifter.

 

Mike

Mileage:331487 Retired/Sold

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You have it right, only the 2004-2005 STi had a 35/65 front/rear torque split. 2006+ is technically 41/59, but that 1% difference (vs 40/60) is splitting hairs :)

 

Btw the 2006+ center diffs have, in addition to the clutch back, a gear-based limited slip mechanism similar in effect to a helical LSD (e.g. Torsen, etc). With a 2004-2005 center diff the clutch pack is the only thing limiting slip. That could be good or bad depending on your desires.

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To make your choice extra fun the center diff is not the only difference in STI transmissions between the years.

 

The 2006+ (IIRC) have reinforced (carbon-plated?) synchros. The 2004-2005 synchros tend to wear out after a couple years.

 

The 2007+ have longer/taller 2nd, 3rd, and 4th gears than the 2004-2006 gears. 1st, 5th, and 6th are the same. The 2004-2006 ratios are generally considered better, but it is somewhat a matter of preference, especially depending on how wide your power band is.

 

Last and least, the 2004 has a SureTrack front LSD whereas the 2005+ have a (Subaru-branded) helical LSD. They're both gear-based and perform similarly AFAIK.

 

Since the transmission will be out of the car anyways I suggest swapping in the reinforced synchros if you're going with a 2004-2005 transmission. Consider swapping in gears for whichever ratios you want too, and if you do that consider the JDM gears, which have different ratios than either the older or newer USDM gears. (IIRC the JDM ratios are similar to the older USDM ratios with a shorter 5th and 6th, but I might be misremembering.)

Edited by matt
removed wrong info - final drive is not the same
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I've been sifting through this thread and some others, and I'm putting together a shopping list... My goal is to end up with the following: 6MT, DCCD, R180, no R160 parts or EAT parts, Torsen diffs front and rear, and 35F/65R torque split. Parts list so far:

 

04-05 STI 6MT (3.9 FD)

07+ STI R180 (3.9 FD, I think?)

07-09 SpecB driveshaft

07-09 SpecB rear axles (P/N 28421AG03B), axle seals (P/N 806732200)

 

6MT rear tranny mount

07 Spec B shift linkage

specB or STI flywheel,

flywheel bolts,

STI clutch (not sure which yet...)

clutch slave cylinder

shift fork

goodridge SS clutch hose

Spiider DCCD controller

 

Am I on the right track so far? Can I get a sanity check?

 

Thanks!

 

EDIT: well, crap. I have conflicting info about which 6MTs have 35/65 vs 40/60.

 

I'm fairly certain the only 3.9 R180 is the 04-05 as they have the 1:1 transfer gear. The others have 3.54 rear diffs and 3.9 front with a 1:1.1 reduction. At least I know 2007 is 3.54, however they may have changed it again for 2008 but I really don't think they did.

 

EDIT: looked on cars101 and it verified that the 07+ is 3.54 rear diff final drive.

 

I'll have to do some more research but those are the things that stuck out to me initially.

 

Also the 04-05 are the transmissions with 35/65 split with dccd open.

 

Ben

Edited by sixspeedlegacy
verified info
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  • 1 month later...

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.

***** Cars101.com 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 - 41310AT040 (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: http://legacygt.com/forums/showthread.php/sti-6-speed-swap-05-gt-61199.html?t=61199

sti_lusts's thread: http://legacygt.com/forums/showthread.php/6-speed-transmission-conversion-my-05-54771.html?t=54771

LegacyGT.com 6MT swap thread: http://legacygt.com/forums/showthread.php/6mt-master-swap-thread-107137.html

BDII's NES 6MT swap thread: http://www.newenglandsubarus.com/forums/showthread.php?t=13187

NASIOC.com 6MT swap thread: http://forums.nasioc.com/forums/showthread.php?t=1201152

An Impreza 6MT swap: http://forums.nasioc.com/forums/showthread.php?threadid=872902

A thread with some DccdPro info: http://forums.nasioc.com/forums/showthread.php?t=2032099

Info about differential types: http://forums.nasioc.com/forums/showthread.php?t=423584

Spec B shifter assembly: http://opposedforces.com/parts/legacy/us_b13/type_12/manipulation/manual_gear_shift_system/

 

Part sources:

 

Millenium Auto - http://www.y2kimports.com/ (Used Subaru parts, including 6MT transmissions)

Silverline Automotive - http://www.silverlineautomotive.com/ (6MT swap packages)

Thrash - http://www.thrashdriveshaft.com/ (custom driveshaft, $650ish)

Spiider - http://www.dccdpro.com/ (Aftermarket DCCD controller)

SGP - http://www.subarugenuineparts.com/ (Axles, seals, clutch fork, etc)

 

Instructional video:

[ame=http://www.youtube.com/watch?v=SxS2XLJqp7M]YouTube - Subaru WRC Gearbox Change[/ame]

Edited by NSFW
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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 http://www.thrashdriveshaft.com/ (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. :)

Edited by NSFW
copied in the pricing info from post #32
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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...

 

http://i193.photobucket.com/albums/z151/Legacy_NSFW/6MT/DSC_0003.jpg

 

http://i193.photobucket.com/albums/z151/Legacy_NSFW/6MT/DSC_0005.jpg

 

http://i193.photobucket.com/albums/z151/Legacy_NSFW/6MT/DSC_0008.jpg

Edited by NSFW
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Start by removing these, and the front axles too:

 

http://i193.photobucket.com/albums/z151/Legacy_NSFW/6MT/OldDriveTrain.jpg

 

So you're left with this:

 

http://i193.photobucket.com/albums/z151/Legacy_NSFW/6MT/NoDriveTrain.jpg

 

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

 

http://i193.photobucket.com/albums/z151/Legacy_NSFW/6MT/FlyingClutchFork.jpg

 

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:

Edited by NSFW
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Almost too pretty to cover up:

 

http://i193.photobucket.com/albums/z151/Legacy_NSFW/6MT/Exedy.jpg

 

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

 

http://i193.photobucket.com/albums/z151/Legacy_NSFW/6MT/Twins.jpg

 

Driveshaft comparison:

 

http://i193.photobucket.com/albums/z151/Legacy_NSFW/6MT/Shafts.jpg

 

And of course the driveshaft plugs into this:

 

http://i193.photobucket.com/albums/z151/Legacy_NSFW/6MT/DiffInstalled.jpg

Edited by NSFW
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First impressions:

 

The clutch pedal doesn't take much effort, and it grabs hard.

In 6th, 70 mph is about 2700 RPM. Cuz I'm doing this for the mileage, you know. :)

As expected, the clutch is noisy when you hold the pedal down. So I'm using neutral more.

The reverse lights are a little flaky. They usually work, but sometimes it takes a couple tries.

The STI shift lever feels nice. About the same throw as my Cobb lever, but taller (and I had the Cobb set as tall as possible).

Haven't really pushed it hard yet, but I'm looking forward to it...

 

More impressions:

 

With DCCD off, a hard launch will spin the rear wheels on dry pavement.

I am starting to get the hang of shifting without losing all boost. It's hard on the car, but it adds 10mph to my trap speed. :)

Looking forward to getting DCCD hooked up...

 

More impressions:

 

Giving it throttle in corners makes the car want to oversteer on the track. Super fun. Still no DCCD yet.

 

More impressions:

 

I talked with a guy who has a GT3071R on E85 making ridiculous amounts of torque. Twice he has broken both a front and rear driveshaft on the same launch. His theory (which totally makes sense to me) is that as soon as a rear axle snaps, the center diff transfers all torque to the fronts, which are weaker, and one of those will break immediately. So I leave DCCD off for drag racing (in spite of busting my ass to get it hooked up the afternoon before a race day, I changed my mind about it at the last second). I get some rear wheel spin but the car still launches pretty well. On my first time at the track the timing system wasn't working, but on my second time out, I got these 60' times:

 

1.917

1.587

1.384 (I did not think that a stock-location 30R could do that)

1.738

 

Most importantly, nothing broke. Those launches were all done by holding around 4500 RPM (no boost), lifting the clutch abruptly, and stomping the throttle. I might have stomped too soon for the 1.38, so maybe I should try launching at a higher RPM.

 

And even though I have the DccdPro controller hooked up I haven't got much to say about it except that when I turn it up too far, I can feel it working against me. Can't wait to try DCCD on a track that has turns in it.

 

More impressions:

 

The clutch is now quiet at idle, with the clutch pedal pressed. I can't hear it at all from the driver's seat, but I haven't checked from outside the car. It has been this quiet for quite some time, I just didn't think to update this post. It's still audible when shifting, and when starting up, but not as much as in the beginning. I'm told that after a while enough clutch dust builds up to suppress the rattle noise.

 

Also, the amount of wheelspin I get when launching depends a lot on the track. At Portland Int'l, I was getting what seemed like just the right amount of wheelspin to prevent bogging. At Bremerton, with DCCD still off, I got zero wheelspin no matter how hard I tried, so I had to (learn to) slip the clutch instead.

Edited by NSFW
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Great compilation! I appreciate the level of detail in the formatting.

 

I look forward to seeing your progress and maybe doing this myself one day. :)

 

The 35/65 split is nice but you have to accept the open center diff. Why not go with the 41/59 split of the '06+ STI and use DCCD to dial it to a more rearward bias, and get a slick helical center diff?

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Thanks. :)

 

DCCD doesn't actually change the front/rear bias, it only changes the lockup. I want more rear bias in hopes of getting more throttle oversteer coming out of turns. The difference between 65 and 59 may be small, but I want to avoid doing anything twice, or wondering I should have done something differently.

 

I actually like the idea of a lockable open diff. I'm guessing that the open diff will help with the throttle oversteer that I'm hoping for. The helical probably responds a bit quicker when one end starts slipping, but that's a lot less important to me.

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I went back and forth between "oh cool gotta do this" and "there are better things I could spend $thousands on," more than once in the last year or three. And to be honest, I'm still not entirely at peace with what I'm about to do.

 

I thought I was done with big expenses. I bought a 3076 because it was the biggest turbo I could get that wouldn't need drivetrain upgrades. But eventually the temptation became too great, so here I am anyway. :lol:

 

I don't have a timeline for getting this done, but I figure it's probably going to take a few weeks to get all the parts together. We'll see...

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One other thing to consider is whether or not your have any aftermarket wires running through the firewall. On my spec.B, the passthrough grommet most people use to run wires is occupied by the clutch master(?) cylinder. After staring for hours at the driver's side firewall looking for the magic grommet that everyone references on this site, I finally realized that it was occupied and ended up having to run my LC-1 wires through the main wiring harness on the passenger side.
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Hammer Down - Thanks, I've made the correction.

 

spec.B Dream - I went looking for that same grommet on my car when I installed my WBO2, and ended up running mine through the passenger side as well. :)

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Hola,

 

I saw the answer to my question on the first page but would like to get more information. I have a 5EAT and would like to install a 6MT capable of 500hp+, is this possible?

 

I did some research on the transmissions and had trouble finding anything.

 

Thanks

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Rallispec's key person is on vacation, so no word about a 6MT yet.

 

I called Thrash driveshaft (aka Driveshaft Specialist Inc) and they had no idea what I was talking about. They did offer to get me an OEM drive shaft, but I was kinda looking forward to something rebuildable and even stronger.

 

Hammer Down, do you have any theories how I might be able to jog their memory?

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