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Old 05-21-2009, 05:23 PM   #1 (permalink)
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Default Best Subaru Transmission?

What is the best standard transmission that Subaru has built. We're all aware of the weaknesses of the 02 WRX but I'm curious to know how strong the XT transmissions is compared to the other turbo'd Subaru models. Also, does the XT share it's transmission with any other Subaru models.
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Old 05-21-2009, 05:46 PM   #2 (permalink)
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They are all the same. Any differences are marginal.

The "best" ones are the ones with a high final drive (like the FXT), or with the LGT gears (08 WRX, LGT) as they are marginally larger. If you are going to spend the money... non OEM is the only way to go.
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Old 05-21-2009, 06:15 PM   #3 (permalink)
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So there's not a transmission that is stronger then another?
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Old 05-21-2009, 06:21 PM   #4 (permalink)
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The STi 6speed is the strongest out of the box or out a wrecked STi...


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Old 05-21-2009, 08:19 PM   #5 (permalink)
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dont buy ppgs
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Old 05-21-2009, 08:32 PM   #6 (permalink)
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So there's not a transmission that is stronger then another?
Not for the 5-speed. The 6MT is stronger than the 5MT, but that swap is such a pain in the butt.

If you want strong, go PPG. Failures are a needle in a haystack for that gearset. There have only been a handful of failures in thousands upon thousands of gearsets sold.
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Old 05-21-2009, 11:28 PM   #7 (permalink)
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With others on this, all the 5 speed clusters have basically the same parts, the close ratio (JDM STI homologation( clusters are marginally sronger as the don't have the smaller gears, but that would hold true of any transmission. Taller final drives are stronger as the pinion gear has more teeth and is the weakest link, PPG is a lot stronger than stock Subaru parts, but is obviously still breakable with enough torque/traction!

6-speed is tougher than 5 by a big margin, but the swap is a pain and its also a lot heavier (about 40lbs I belive)

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Old 05-22-2009, 02:43 AM   #8 (permalink)
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With others on this, all the 5 speed clusters have basically the same parts, the close ratio (JDM STI homologation( clusters are marginally sronger as the don't have the smaller gears, but that would hold true of any transmission.
The JDM STi gears are no wider than the newer age WRX/FXT gears. They do have a benefit of shorter gear ratios, which reduces the ultimate load on the gears themselves.

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Taller final drives are stronger as the pinion gear has more teeth and is the weakest link, PPG is a lot stronger than stock Subaru parts, but is obviously still breakable with enough torque/traction!
The pinion gear isn't the weakest link. Like above, a taller final drive reduces stress on the gears. That is why the taller final drives are stronger. The only reason ring/pinion failures occur is from the wrong fluid being used. The weak link behind the gearset itself is the transfer gears. PPG makes replacement transfer gears for that reason.

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6-speed is tougher than 5 by a big margin, but the swap is a pain and its also a lot heavier (about 40lbs I belive)

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The 6MT is about 80lbs heavier after the whole swap (closer to 100 with the rear diff and everything. A little more if you do the brembos and such too). The strength of a 6MT is marginal compared to a 5MT. The shorter gear ratios are really the only thing that provides an advantage over a PPG 5MT in the strength department.
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Old 05-22-2009, 04:05 AM   #9 (permalink)
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Not for the 5-speed. The 6MT is stronger than the 5MT, but that swap is such a pain in the butt.

If you want strong, go PPG. Failures are a needle in a haystack for that gearset. There have only been a handful of failures in thousands upon thousands of gearsets sold.
what happens when they do fail though?
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Old 05-22-2009, 04:15 AM   #10 (permalink)
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Replace them?

You are lying to yourself if you think going to a 6-speed will solve gear breakage issues.
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Old 05-22-2009, 04:35 AM   #11 (permalink)
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so you get to pay thousands of $ more than once for gears, even when their horsepower ratings aren't accurate?

I realize that you guys deal with more ppg gears than anyone in the world but I am just basing my opinion on my situation
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Old 05-26-2009, 12:45 AM   #12 (permalink)
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The JDM STi gears are no wider than the newer age WRX/FXT gears. They do have a benefit of shorter gear ratios, which reduces the ultimate load on the gears themselves.
Indeed who said they were? Where you have a ratio closer to 1:1 (as in JDM sti close ratio box) the 'smaller' (less teeth) gear in each ratio pair is 'bigger' (has more teeth) hence a close ratio box (where 1st is taller than other boxes and fifth less overdrive) is stronger as its the smaller gear that is the weaker in any pair. The loading on the GEARS is proportional to torque, so what you say is wrong, the loading on the TEETH is reduced as more are in contact at any one time.

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The pinion gear isn't the weakest link. Like above, a taller final drive reduces stress on the gears. That is why the taller final drives are stronger. The only reason ring/pinion failures occur is from the wrong fluid being used. The weak link behind the gearset itself is the transfer gears. PPG makes replacement transfer gears for that reason.
Actually same as above, of the CW and P, the pinion IS the weaker link - less teeth again! Again as torque is the load input, having a taller FDR doesn't reduce the load at all, its only that taller FDR boxes usually go with a wide ratio gearset (so taller fifth and less torque multiplication through fifth gear than a close ratio box) that makes pinion failure less likely, but that depends on usage, a rally car (assuming its stuck with homologated wide ratios) spend little time in top!

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Old 05-27-2009, 05:38 AM   #13 (permalink)
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Originally Posted by The Rookie View Post
Indeed who said they were? Where you have a ratio closer to 1:1 (as in JDM sti close ratio box) the 'smaller' (less teeth) gear in each ratio pair is 'bigger' (has more teeth) hence a close ratio box (where 1st is taller than other boxes and fifth less overdrive) is stronger as its the smaller gear that is the weaker in any pair. The loading on the GEARS is proportional to torque, so what you say is wrong, the loading on the TEETH is reduced as more are in contact at any one time.
I don't know. You said the JDM boxes don't have the smaller gears. I assumed you meant width.

I don't believe you are correct in your opinion that more teeth are in contact at any one time with a variation in gear ratio. Two circles can only meet at one point, right? That point of contact doesn't change with a change in gear diameter. Contact patch has nothing to do with gear diameter. Tooth count, similarly, has little to do with contact area. Teeth can only be engaged when they line up. The point of maximal contact is when the teeth are parallel to each other. Only one tooth from each gear can be in maximum contact at any given time. The number of teeth you have can't change this. Tooth count is proportional to diameter. Smaller gear, fewer teeth. Bigger gear, more teeth. At full tooth engagement, any transition engagement is marginal, dwarfed by the pressure at the engaged tooth. Only one tooth can be fully engaged at a time. The strength of numerically taller ratios has very little to do with tooth count and everything to do with tooth profile and width.


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Actually same as above, of the CW and P, the pinion IS the weaker link - less teeth again! Again as torque is the load input, having a taller FDR doesn't reduce the load at all, its only that taller FDR boxes usually go with a wide ratio gearset (so taller fifth and less torque multiplication through fifth gear than a close ratio box) that makes pinion failure less likely, but that depends on usage, a rally car (assuming its stuck with homologated wide ratios) spend little time in top!

Simon
And yet, no one breaks final drives. Transfer gears are the weak link after the gearset. There is no contest about this. Subaru actually follows no regimen for matching gear ratios to FDR. High FDR's, like the Forester, still mostly share gear ratios with the lower FDR boxes. And the JDM STi boxes were high FDR's AND short gear ratios.
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Old 05-27-2009, 05:44 AM   #14 (permalink)
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so you get to pay thousands of $ more than once for gears, even when their horsepower ratings aren't accurate?

I realize that you guys deal with more ppg gears than anyone in the world but I am just basing my opinion on my situation
PPG doesn't "rate" their gears. They simply make recommendations for the power they typically hold. That is very very different.

As for paying thousands more than once, that is between a customer and PPG. I simply say they should be replaced. You'd be fooling yourself if you think a 6-speed is going to cure your problems or prove more reliable.
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