2004 sti six speed conversion

[farawayjeff]

Has anyone completed the 2wd conversion on a 2004 sti six speed without using the Possum Bourne adapter? The kind folks at PB are no longer offering that part unfortunately. Looking for help. Not sure what to do now.

Jeff

[Zach34]

I converted my 2005 with the Possum Borne adapter. I saw no easy way to weld the 2005 center diff. If it's the same as the 2004, I don't think you have a good option other than trading the trans for one that can be converted with the FFR kit. The Possum Borne part was expensive, but broaching those splines is not cheap machine work, and it has to be hardened as the gears are.

[Hindsight]

What are the differences between the 6-speeds from various years? I thought 04-07 were all the same?

[farawayjeff]

The Internet tells me that in 2006 the center diff was changed (to a limited slip). It doesn't tell me how to lock the 2004-05 center diff other than the no longer available Possum Bourne adapter. I was hoping someone here was smarter than the Internet. I am not by far. I really wanted to avoid having to sell my trans and buy another.

[STiPWRD]

There's some info in this thread:
http://thefactoryfiveforum.com/showthread.php?16920-STI-Six-speed-DCCD-2WD-Conversion-Issue

and here:
http://thefactoryfiveforum.com/showthread.php?17256-Fryguy-s-818R-with-2004-STI-Donor-Build-Thread

If the adapter is no longer sold commercially, there's not much you can do other than trying to reverse engineer one and have it machined/hardened yourself. This would require having access to parts that you could measure and make drawings of.

[Scargo]

First, a caveat: I have not completely finished the process with my 818R conversion. I have, however, rebuilt several six-speeds.
2006+ USDM's are different and have slightly different center diffs and final drive ratio. The final drive ratio is irrelevant to the conversion. Pre-2006 USDM diffs are not interchangeable. A workaround is to sell what you have and buy a JDM tranny with the correct diff for the adapter.
This chart will help. (http://home.gci.net/~cowdookey/818/TransmissionIDChart_Public.pdf) I got a great '06 JDM tranny from J-Spec Auto Sports in VA (https://www.jspecauto.com/contacts.htm). And it comes as a close-ratio box and oil pump. This means that you can easily add an oil cooler to it.

[farawayjeff]

Thank you for the chart, Scargo. I've almost finished the six stages of grief. I will start my search for an 06-07 sti 6 speed trans tomorrow.

Thank you all for helping me sort this one out. Wish the outcome was different, but it's good to at least know what I need to do.

Cheers

Jeff

[Zach34]

That first thread that STiPWRD posted has some of my posts as I struggled with this issue. I really didn't want to spend the money on the Possum Borne adapter. The video in one of my posts in that thread suggests a method that could be tried, but after I made that video I did some more measuring and was not sure how much spline engagement I would get if I proceeded as I suggested. That prompted me to envision the transmission, which I was about to spend a lot of money on getting rebuilt with all new gears, exploding due to my well-meaning but insufficiently-strong conversion attempt. That's when I ordered the Possum Borne adapter.

The price made more sense when I got it in my hands. A low-production run of those kind of parts will be super expensive, and most shops who have the equipment to do it will probably not want to deal with a small-quantity order.

[Aero STI]

I welded up the internals of a 2004-2005 DCCD. It has been holding strong.

http://i.imgur.com/YQ1nnra.jpg

Once you get into the transmission it become pretty obvious how to get the center differential locked up.

BTW, I'm using a 2003 Forester STI 6 speed.

[farawayjeff]

Glad to see there is actually a way to do it. Unfortunately, I already purchased a 2006 and the ffr adapter. So the 2004 is now for sale for $2k. There is probably a lesson in patience here for me.