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6 speed swap help!

('06-'08) 
2K views 0 replies 1 participant last post by  hyogong57 
#1 ·
I could use some technical advice if you can lend an ear. This work was done on a UDSM 08 Forester Sports 5MT being swapped out for a JDM V7 STI 6-speed transmission.

I bought a 01-02 JDM V7 STI transmission. TY856WB1AA its the same final drive, transfer ratio, and rear differential 3.900 FD as USDM 04+ STI. The only differences is the 5,6th gear ratios.

I swapped out the front open differential with a 05 STI helical. Had a professional shop do it correctly. Then, I ended up using an 04 STI rear differential case and replaced the plated rear diff with the Suretrac one from a 04 JDM SG9 STI.

The JDM SG9 STI tranny was TY856WL4CC. Same final drive, transfer ratio, but the gear ratios are totally different all the way through 1-6 Obviously.

The Suretrac went in no problem, Helical the same. I used an 04 STI drive shaft and replaced all subframes and crossmembers with 04 STI parts. the angle of the drive shaft is perfect and I dont have issues with it banging against the undercarriage components. I removed those spacers on the FXT front crossmember before putting the STI one in and replaced the steering U joint with STI as to make sure that the STI driveshaft would work correctly.

The tech who did the work test drove it and found that a knocking noise, shuddering type noise or simliar type feel would occur after a few minutes. The car in neutral will not move after this sound happens while stopped. The diffs lock up, and since there is no DCCD, the power split is 50/50. It seems that after a few minutes of driving the differentials seem to do this. The gears are all accessible. No grinding on shifting.

One issue could be that the wheel size/tire size difference is causing it? IE: I was involved in an accident and one of the wheels was bent out of shape and destroyed. I was running 18x8 5x100, +44, 245/40/18 but one wheel was 17x7.5 225/55/17 because I didnt have a replacement.

I finally got a replacement wheel 18x8 5x100 +44 same tire size but different brand. and it was slightly ever so slightly smaller cause of the wall of the wheel construction just was that way. Toyo vs Falken.

I'm set to get a brand new set tomorrow to eliminate that problem and hopefully the issue will be resolved. But wanted to get your opinions on the matter.

Id love to hear technical advice on this and hoping to resolve the issues quickly.
 
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