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Thread: 30/70 rear bias with junkyard parts

  1. #1
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    30/70 rear bias with junkyard parts

    So I was getting back up to speed on electronic couplers and I found this explanation of the system in the gr yaris:

    https://youtu.be/PvXuryayDn4

    Tldr it uses a coupler very similar to ours but it achieves a 30/70 f/r bias by using a 1% faster gear ratio in the rear.

    So, that said, the 2007-09 automatic is geared 4.38 at the rear versus 4.41 for the manual. The difference is about 1%.
    Swapping a salvaged automatic rear carrier into a manual should make for a rear biased awd then, right?

    Someone smarter than me take a look at this and tell me what you think.
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  2. #2
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    I might have gotten it backwards and the front ratio needs to be changed to the auto 4.38 ratio. Gearing is hard.
    '09 SX4 AWD 5-spd Technology Copper Sunlight Metallic - RIP
    '15 Ford Fiesta ST Tuxedo Black, Stage 2+ E30 tuned
    '09 SX4 AWD 5-spd Touring Copper Sunlight Metallic - v2.0

  3. #3
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    This would never work. It would just wear out your clutch pack faster. The front is driven by gears off the transmission, and the rear is driven off of that, with a semi-slipping clutch pack that engages and disengages in pulses. The awd system is one where the rear supplements the front.
    2007 SX4 Hatchback J20A Manual, turbo install in progress; http://clubsx4.com/forum/showthread.php?t=8665
    also own a 1996 X90 4wd 4 inch lift on 30's G16B Manual

  4. #4
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    Quote Originally Posted by Stehignite View Post
    This would never work. It would just wear out your clutch pack faster. The front is driven by gears off the transmission, and the rear is driven off of that, with a semi-slipping clutch pack that engages and disengages in pulses. The awd system is one where the rear supplements the front.
    It doesn't pulse, we used to think that before documentation on how our system works became available but to quote LeVar Burton "don't take my word for it".

    https://studylib.net/doc/10702247/el...e--emcd%C2%AE-

    Anyway, that's exactly how the unit on the GR yaris works. Admittedly I believe it has more clutches but it's also dealing with twice the power. The yaris is also primarily fwd with a transfer case driving a prop shaft to an electro magnetic clutch pack which in turn sends power to the rear differential. You say it wouldn't work but Toyota has proven otherwise.
    '09 SX4 AWD 5-spd Technology Copper Sunlight Metallic - RIP
    '15 Ford Fiesta ST Tuxedo Black, Stage 2+ E30 tuned
    '09 SX4 AWD 5-spd Touring Copper Sunlight Metallic - v2.0

  5. #5
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    Watch the video again, then rewind to the 1:30 mark. Compare that to the link I posted above. The jtekt itcc is identical in form and function as our gkn emcd. Without the 1% difference in gear ratio front vs rear it would function just like our system, only getting up to 50/50 split. Yes it has different modes but that's just the e-diff controller controlling the pressure on the clutch pack differently than ours does. The yaris has 60/40, 50/50, and 30/70. We would have 100/0 in "off", 100/0 - 30/70 in "auto", and full time 30/70 in "lock". This wouldn't do anything for the speed cut off in lock mode but we already have an aftermarket solution for that. This is do-able. The real question is is it worth it?
    Last edited by Die trying; June 1st, 2021 at 02:42 PM.
    '09 SX4 AWD 5-spd Technology Copper Sunlight Metallic - RIP
    '15 Ford Fiesta ST Tuxedo Black, Stage 2+ E30 tuned
    '09 SX4 AWD 5-spd Touring Copper Sunlight Metallic - v2.0

  6. #6
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    Sherbrooke, Quebec, Canada
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    It's worth a try

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