STI Six-speed DCCD 2WD Conversion Issue

After lurking for awhile on these forums and learning a lot, it is time to contribute and hopefully help someone else out with my first post. Unfortunately, it’s an issue with the STI six-speed conversion. I do have an email out to FFR (Jay), so I’ll definitely post the followup. My donor is a 2004 STI (I am the original owner). The center differential looks very different than what is seen in the six-speed conversion guide. It doesn’t look the 2WD adapter will work with this drive flange. Doing research on the internet, it seems like the 2004-2005 STI DCCDs are different than the 2006-2007? That’s a guess from seeing different overhaul kits. For reference, the part number on this transmission is TY856WH3MA. Any subie experts out there have any thoughts? Anybody know the history of the DCCD changes?

2WD adapter and my drive flange (with oil pump drive gear):
Attachment 38360

Drive flange From the guide (with oil pump drive gear removed):
Attachment 38361

2WD adapter attached to the drive flange from the guide:
Attachment 38365

Pic of my disassembled DCCD with the 2WD adapter on the left, drive flange, clutch disks, center section:
Attachment 38362

Jeff

Thought I'd post an update on this. Jay got back to me and is still doing research on the issue. He did confirm that they used an 06 and an 07 STI on their builds. My research on nasioc is indicating that the 04-05 have a different center diff. I'll wait on FFR to confirm. Stay tuned.

Jeff

So heard back from FFR on this issue and the unfortunate news is that the adapter won't work for my 2004 STI. FFR is going to refund the six-speed option. For others looking at a six-speed, I can only confirm 100% that this is an issue with DCCD part number 38913AA160 in the transmission TY856WH3MA for the 2004 STI. It does look like the same DCCD part number is used on the 2005 STI, but the transmission part number is different. So I am guessing 2005 STI is out as well. 2006-2007 STI have a different DCCD part number and these are the donors used by FFR.

Hope is not completely lost though. I have an inquiry out to Possum Bourne Motorsports in New Zealand. They confirm that their center diff locking adapter will work. I am trying to get more details at this point.

Attachment 39264
http://possumbourne.co.nz/trans-and-diff-parts.html


Transmission, DCCD part no reference:
http://home.gci.net/~cowdookey/818/TransmissionIDChart_Public.pdf"]http://home.gci.net/~cowdookey/818/TransmissionIDChart_Public.pdf"]http://home.gci.net/~cowdookey/818/TransmissionIDChart_Public.pdf

yeah those possum pieces are nice but $800 usd iirc.

Quote:

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Originally Posted by longislandwrx

yeah those possum pieces are nice but $800 usd iirc.

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Do you know of anyone that used these for a 2004/5 STI 6-speed?

So I ordered this center locking diff spool from Possum Bourne. It ended up costing about $1K with shipping. I'll update this thread once I get it.

Jeff, I'm using a 2005 STI donor. I just started the 6-speed FWD conversion and of course ran into the exact same issue you posted about. My trans has the oil pump driven by the center diff and the parts look precisely like the pictures you posted.

I can't understand the price for that Possum kit.

A few thoughts:

-There are two concentric splined shafts, that either drive or are driven by the center diff. I'll call the large hollow splined shaft the "outer" shaft/splines and I guess they seem to drive the center diff (could be wrong). The "inner" shaft/splines are threaded through the outer shaft/splines and drive the rear wheels? The outer splines drive the flange of the center diff that contains the oil pump drive gear.

-It seems that the only purpose of the adapter flange supplied in the kit is to lock the "outer" splines to the "inner" splines. Is this correct? What does the inner shaft drive apart from the rear wheels that would necessitate it being locked to the outer splines?

If my thinking is right, it seems like the adapter flange could just be welded to our oil pump drive flange. Some measurements will have to be taken to make sure the adapter flange isn't too short or too long. Could this work?

If not, where did FFR source their adapter flanges? I'm guessing these things have to be hardened.

I don't want to drop $1k on this...

Yes, that was exactly what I was initially thinking: weld to the drive flange and figure out the correct length of the adapter. After FFR confirmed that the adapter was not going work, I asked what was the purpose of the adapter. Was it there to just hold the drive flange on? And does the other end of the adapter need to butt up against the tail housing to hold it on? I have not received a response yet on that. The problem is that I don't feel comfortable welding the adapter to the flange and trying to figure out the correct length. I don't want to risk damaging the transmission. I already ordered the Possum kit. I don't mind taking measurements for you or anything else if you want to attempt your own solution.

FFR didn't reveal who their supplier was to me. But it appeared that they were relying on the supplier for answers and they weren't responsive.

OK, I talked to Tony at FFR today. He suggested that he may have heard of somebody welding the adapter on one of these center diffs. Most importantly, he confirmed what I suspected, after looking at the diff and some diagrams: The purpose of the conversion kit is to lock the "driven" shaft of the transmission to the "pinion" shaft for the front differential. The attached diagram shows what I'm talking about and should make it pretty clear. The center diff is normally driven by the shaft labelled #8. The front differential pinion gear is part #1. Since we don't have to split power between the front and rear wheels anymore, all we need to do is lock those two shafts together. That's what the adapter does.

I think I may have figured out a solution using the FFR 6MT kit. Instead of writing a dissertation, here's a shoddy video I hastily shot explaining what I have in mind. I sent a link to Tony, and I'm waiting to hear from him to confirm that I'm on the right track.

http://youtu.be/MfcI_CB_XN0

I have some reservations about welding it, but I think I'm going to attempt it. More to follow on that...

I picked up and 04 STI center diff that was burned out from a local shop in hopes of reselling my 06 center diff and came across the same issue that you have now. I went ahead and used the 06 diff since that was the easier way out.

In addition to bolting the adapter in, I also welded it around the entire perimeter of the flange after V grooving it.

It sounds like youre on the right path just make sure that center smaller shaft is long enough to have sufficient engagement into the adapter.

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

Kurk, how is that retained on the driven shaft? As I illustrated in the video, I think I'll have to retain the center diff housing to keep everything in place. Is the 06 center diff assembly just a lot shorter? Also, what is that additional flange behind the one you welded? Doesn't look like the FFR adapter, unless it's hidden in there.

That whole assembly goes back into the center diff. Those spaces are where planetary gears used to sit.

I removed just enough of the clutch discs to account for the thickness of the FFR flange. Heres a photo of the coupler welded in from the back side. That center portion is the FFR coupler.

http://i.imgur.com/qy7uYP6l.jpg

I received the center diff locking kit from Possum Bourne. It looks pretty good. Although $1K does seem pretty pricey for what you get. I guess you can do that when you are the only game in town (more like the world).

http://thefactoryfiveforum.com/showt...l=1#post191480

Ah, ok, yeah that's completely different than my center diff. Here's a picture of the whole thing taken apart.

Would swapping in a 06-07 center diff to an 04-05 trans work for the adapter or are there other differences besides the diff?

I'm not sure. I expect there are differences. I have found no evidence of that being possible. I ended up going with the Possum Borne adapter. Extremely expensive, but the adapter requires a lot of machine work and heavy broaching on a low-volume part which is then hardened (and possibly shot peened first), so the price sort of makes sense. Check the exhange rate for AUS $. The adapter is a perfect fit and is much lighter and stronger than my half-baked idea in the video. I'm glad I got it. It's one of those things that you don't want to go out on the track with thinking "gee, I hope it holds up", you know?

I recall the transfer gear part numbers being different depending on which style DCCD. I believe this is because of the change in the transfer gear ratio from 1:1 to 1:1.103. I fit a modified '06-07 DCCD center diff into my '04 Forester STi transmission which came with a limited slip instead of the DCCD. The only problem I ran into was that the center diff assembly was slightly longer than the forester center diff would be so I had to shorten one shaft slightly.

Would a 2008 GR 6 speed work as well or is it a completely different setup?

Quote:

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Originally Posted by iblackwe

Would a 2008 GR 6 speed work as well or is it a completely different setup?

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It can work. The part FFR sells is for a GD (pre-2008) transmission. The DCCD (center diff) is different for the GR's. Note that several people have welded the parts together rather than bolting. You cannot use the FFR piece and bolt it to the later model design of diff. Diffs are not interchangeable.
I believe that this issue is discussed and described in this thread, if not another on this 818 forum. Try searching.
I have a GD six-speed with close-ratio gears, built-in oil pump and an OS Giken LSD setup specifically for the 818 and racing. If this is of interest to you or anyone else PM me. I am thinking I may go with a five-speed. I also have the FFR adapter for the six-speed. The tail end is not modified.

Quote:

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Originally Posted by Scargo

It can work. The part FFR sells is for a GD (pre-2008) transmission. The DCCD (center diff) is different for the GR's. Note that several people have welded the parts together rather than bolting. You cannot use the FFR piece and bolt it to the later model design of diff. Diffs are not interchangeable.
I believe that this issue is discussed and described in this thread, if not another on this 818 forum. Try searching.
I have a GD six-speed with close-ratio gears, built-in oil pump and an OS Giken LSD setup specifically for the 818 and racing. If this is of interest to you or anyone else PM me. I am thinking I may go with a five-speed. I also have the FFR adapter for the six-speed. The tail end is not modified.

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Based on reading up on 6-speed conversions, it seems to me that it is much easier to just buy the FF swap kit and source a 2006-2007 STI 6-speed trans. Creates less headaches...

Do you know if the transmission from the jdm ej207 V9 is compatible or not? I just found this thread.

Do you have a specific part number, like TY856WB XXX? There seems to be changes in that range where there are different center diffs.

Scargo, I'm assuming you sold that tranny?
So, would a 2016 WRX 6 speed work? anybody looked at that? length wise, etc... it kinda look shorter....

I found that there is a JDM 6 speed that works but forgot the years. Compare the approved usdm year center diffs with the JDM center diffs, if they are the same, it should work...

Quote:

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Originally Posted by Doowop

Scargo, I'm assuming you sold that tranny?
So, would a 2016 WRX 6 speed work? anybody looked at that? length wise, etc... it kinda look shorter....

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No, that is a different engine and the transmission closer related to a 5 SPD.

I still have the tranny. If serious PM me. It won't be cheap.

Okay I know I read this somewhere but for the life of me now I can't find where it was documented. Is there a difference with the centre diff in a Spec B legacy 6 speed from 2006?

Thanks if someone can answer that or point me in the right direction of the thread

I tried this with ones I have and they do not interchange. The tail casting and more is different. I have the '04 TY856WH4MA and the JDM '06 TY856WB7KA (close ratio with internal pump). USDM for '06 and '07 has same center DCCD diff. as the JDM '06.
Someone on here did the welding and made it work.
Attachment 65108
I will share my list but it only applies to STi's. I do not know about the Legacy, etc.
Attachment 65107