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Old 06-15-2018, 05:20 PM   #1
mekilljoydammit
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Default How to put a 5 speed RA DCCD center in your Phase 2 transmission (don't)

OK, pictures will follow once I find the pictures I took. First off though, don't do this. I'm writing this because I could never find answers, and I did it, but I also race RX-7s so I'm odd.

Now, I'm writing this in 2018. The most recently sold DCCD diff for the 5 speed is 18 years old at this point, depending on what you are starting with you'll need to hunt down a bunch of extra parts, and you're left with something that still won't hold the power that a 6 speed will. I hunted down parts over years in my spare time - because again, the DCCD centers for the 5 speeds are super rare nowadays.

Don't do this swap. If you have to mess with 5 speed stuff just get a whole transmission and matching final drive. If you really want DCCD and proper diffs, get a 6 speed. It's 2018, there's no good reason to do this anymore.

That said, the easiest way is to get a full RA extension housing - outer aluminum casing, center diff, transfer gears, all in a nice neat package. I did not do that.

At minimum from the RA transmission, you need the DCCD center (duh) and the transfer gear that plugs into the diff. The normal Phase 1 and Phase 2 transfer gears will not plug into the DCCD center. Also, the transfer gear for the DCCD Phase 1 transfer gear is different from all the other transfer gears - I just looked it up by size. You ideally also need the top cover that the plug comes out as it incorporates a feature to align the wiring such that it doesn't get wrapped in the gears although you could probably just modify a Phase 1 top cover with some welded spuds to align the wiring.

You can NOT use a Phase 2 extension housing. If you look at the DCCD center next to a Phase 2 center, the Phase 2 center necks down towards the front of the car, so the DCCD center will physically hit parts of the casing. "Aha," you might be saying. "I have a machine shop, I can just clearance it..." and you'd be wrong. The Phase 1 differentials are physically longer - with it seated, the DCCD center diff sticks past the edge of the case, the Phase 1 transfer gears are different, it does not work. I know because I had that exact thought, chucked the extension housing on my mill and clearanced it.

However, if you're an idiot like me you can get a plain ordinary Phase 1 extension housing and bolt it to the Phase 2 transmission and that does work. I used car-part to get some random 90s Legacy transmission and its casings worked fine.

If you've read this far and are still not deterred, maybe you'll be deterred by me saying "the rest of the job is just like messing with the extension housing" and not do this.
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Old 06-15-2018, 06:30 PM   #2
Zmanwrx23
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While I have no intention of ever performing this swap, and I already have USDM V9 STi swap in my car. I'm very interested to hear more and see pictures. This sounds like a not fun time lol.
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Old 06-15-2018, 07:09 PM   #3
mekilljoydammit
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The big lesson is that you cannot do this without a bunch of Phase 1 parts. I spent a whole bunch of my spare time and killed a Phase 2 extension housing trying to make it work - it won't.

How bad it is depends on what you can find. I started off only being able to find the center diff itself plus the transfer gears - if I'd found the rest of the extension housing it would have been fine. If I'd given up and found a Phase 1 donor trans earlier it would have been fine - physically it's all pretty much plug and play. You just set a mental border saying "OK, in front of the extension housing is Phase 2, behind it is Phase 1" and it bolts together. But other than the springy thing to center the shifter (which seems to have been improved in Phase 2) and bolts, nothing from the Phase 2 box can substitute for any of the Phase 1 stuff.
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Old 06-17-2018, 01:46 PM   #4
mekilljoydammit
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One example of RA-specific parts. That cover on the normal Phase 1 transmissions is flat steel. On the RA it's cast aluminum with features to hold the plug in one orientation, so the wires for the DCCD diff won't get wrapped around shafts or gears. You could probably make a steel non-RA cover do that with cutting and welding though.
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