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Old 02-11-2001, 01:23 AM   #1
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Talking Important information on Durometer testing of my failed 2nd gear!

Well,

Today Dave Scott (with the 350+ hp 15 psi 2.2L wagon, now at 18.5 psi) was getting some turbo Legacy guts (er... gears) installed into his tranny case at JCS today, after he snapped 2nd gear the same week I did mine. He's been driving around with a borrowed 2wd tranny till his got fixed. However, Dave had snapped three teeth off the pinon shaft gear, vs my shearing off ALL but three teeth on the main shaft. The turbo Legacy main shaft is supposed to be the same as the WRX main shaft, and is known to be stronger. And, apparently Byron Leggit even found it harder to break Legacy Turbo gears than newer ones, so this is what they decided to try first (before BPM gears).

In doing the rebuild, they noticed that the color of my failed main shaft (with 2nd gear) was grey, and the color of the Legacy turbo main shaft was golden; so they decided to test my main shaft and the turbo Legacy main shaft for hardness, on a durometer. Mark at JCS took them down to a friends shop, and they found that my main shaft tested at a 1.01 on the durometer, and the turbo legacy tested at 0.92 = 10% softer than mine!

What they found next was that my MY00 main shaft was only "case hardened" (heated and dipped in carbon), and had only a small thin layer of hardened steel on the surface to prevent gear wear, and was probably a 0.50 durometer rating on the inside. Our MY00 gears are like tootsie pops - Hard on the outside and chewy in the center!

The turbo Legacy main shaft was heat treated in a way that would provide the same 0.92 durometer reading all the way through to the center. Therefore, the Legacy turbo gears would have more "meat" to them inside and at the bases, and be harder to break.

The only question is will cryo-treatment, similar to what www.frozenrotors.com does to brakes, make the gears even stronger. To find out, JCS is sending an entire tranny to a shop in Longmont Colorado to be cryo-treated.

I'll keep you posted if I find anything new.

Larry www.ImprezaRS.com
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Old 02-11-2001, 01:59 AM   #2
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I've asked around about cryo treating, and have gotten differing opinions. Some say it'll interfere with the gears heat treat and make them weaker. Others think it could help to varying degrees. Be interesting to see what happens with this one
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Old 02-11-2001, 09:13 PM   #3
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Good work Larry!!! This is great news, Legacy Turbo gears instead of an expensive BPM gearset seems to be a cost-effective way to upgrade our RS gears. I hope to hear good results on the Cryo'd gearset. Do you know what year tranny JC sent to get cryo'd? I sure hope the results of this test is more timely than JC's turbo group buy.
Zee
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Old 02-11-2001, 09:24 PM   #4
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I thought that the case hardening of the teeth while maintaining a softer center was a good thing. When I was on co-op this past spring/summer and did some testing with gears we were heat treating, this was what I was told. It allows for the hardness of the case-heat treated part of the tooth to resist wear, while the softness of the inside helped increase strength. If the whole tooth was hardened, it would be brittle and break off esaily. By being softer, there is more "play" at the base of the tooth allowing it to absorb more power before snapping off.

This is just what I remember being told by the people in the heat treat department. I don't remember what the ratio of tooth face hardness to interior tooth hardness was though. We also dealt with powered metal (steel), but I would assume that the same principles would pertain to the shafts or gear sets in our trannys, correct?

Just something I remembered from work here and wanted to bring up.
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Old 02-11-2001, 09:40 PM   #5
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Its the same philosophy with good combat swords. If you take a standard wall hanger sword say a through and through 440 stainless sword and go at it. You will shatter the sword, as it is too hard /w no resilience. OTOH if you get your hands on a nice laminated blade with a (soft) high carbon core, you can beat it all day without fear of shattering (except the occational nicking of the blade).

The softer core of the RS gears allow it to take a greater shock without shattering. Absolute strength is something else, especially if the 2.2 gears are lasting longer.

The cryo treatment is suppose to remove structural stress in the metals which in turn helps it to last longer.
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Old 02-12-2001, 01:39 AM   #6
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Well just looking at one aspect of the material is pointless. Look at (true) cast iron. Its soft and dense, yet it shatters almost like glass. Great for making bases for machinery, bad for most other things.

So just looking at how hard the material is is not terribly useful. It is important but so is many other properties. I would bet that the turbo Legacy uses a much better process when its created than the 2.5RS one. This can lead to a stronger and harder gearset.

BTW its nice that softer materials tend to absorb loads better than stiffer ones, but AL, and to a lesser extent Ti like to smear when used in applications like gears. This is why my old RC car has a steel gear that looks new, and the factory Al one that looks like its been 1/2 melted and the teeth are no longer a proper shape.
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Old 02-12-2001, 02:02 AM   #7
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I want my tranny to be made the same way the "green destiny" sword was on Crouching Tiger, Hidden Dragon....

yeah I know it would never happen but it would be GREAT!
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Old 02-12-2001, 08:10 AM   #8
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RawCode,

Good luck stealing the Destiny sword from that dude! Your better off shelling out the big bucks for a new STI tranny.
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Old 02-12-2001, 11:25 AM   #9
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I agree with the dual density model, a soft center less likely to shatter and the case hardening makes the gears wear less on the outside - but how soft is too soft, how hard is too hard? That is the question.

The 10% softer legacy turbo mainshaft being one hardness all the way through seems to hold up well in the WRX, since they are the same part (we are told)...
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Old 02-12-2001, 03:42 PM   #10
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Now my question is where can we source out just the legacy main shaft without needing to buy an entire tranny. I kind of doubt a junk yard is going to simply pull the mainshaft for me. I do have a legacy turbo local to me though

...Now I want to see Crouching Tiger, Hidden Dragon again!!

[This message has been edited by stimpy (edited February 12, 2001).]
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Old 02-12-2001, 04:07 PM   #11
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JC Sports buys used or broken trannys to rebuild, they might know where to get them.

Or you can get from a junk yard, or you can also buy the main shaft new for about $350 or so (that's what a MY00 mainshaft costs, and I got my used one for half price when a turbo legacy one wasn't available STAT).

Larry
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Old 02-21-2001, 11:18 AM   #12
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What about gearing on the legacy mainshaft. Aren't the legacies geared differently? Is it going to force a different gear ratio in 1st and 2nd or is everything all the same; minus the fact that the legacy mainshaft is stronger?

-Jon
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Old 02-21-2001, 12:39 PM   #13
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YOu get a gearing change when you do the entire legacy gear set, main shaft and pinon shaft - I'm told 35mph in 1st and 60 in 2nd.

Larry
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Old 02-21-2001, 02:58 PM   #14
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What year legacys were these? I have a friend with access to a national database of salvaged automotive parts. I'll see what I can find for anyone interested, but I need all the detail I can get about the cars year/make/model/etc.

Thanks!
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Old 02-21-2001, 03:03 PM   #15
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Thanks Dan_E!
The legacy turbos were sold as a MY91-MY94 car. The models were the legacy sports sedan and touring wagon. I think that the wagons only came with an auto tranny and the sports sedans only come with a manual tranny, but I have not confirmed this. The information came from DLC (he drives a touring wagong, so he probably knows best).
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Old 02-21-2001, 11:11 PM   #16
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My understanding on the notorious Subie trannies is that the length of the main shaft is actually relatively long and when you run a lot of torque through the box, it actually causes the mainshaft to deflect/bend so that the gear teeth can begin to pull apart.

If you torque the tranny too hard the teeth will actually come apart and this is when the teeth shearing starts. If the Legacy's shaft is harder (read...stronger) it will be less prone to bending therefore less tendancy to deflect and therefore a better choice even with the softer teeth.
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Old 02-21-2001, 11:23 PM   #17
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good theories...

Larry
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Old 02-21-2001, 11:26 PM   #18
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Larry,

IIRC, I got that info here on the board from a posting from Rigoli after he hit the 10.1 1/4 mile. You should do a search I believe its there.
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Old 02-22-2001, 08:30 AM   #19
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I have heard a lot of stories about the incredibly weak 2nd gear that our cars seem to have.

I myself dont have any problems with the transmission, but have read many posts on it. It seems that their is a common feeling that we have weak second gears. I do not think this is an entirely true statement. It is no coincidence that 2nd gear is the one that appears to be failing more. What gear gets hit harder than 2nd. Most people usually dont drop the clutch in first, so it is not pounded. However, with the large jump in ratios from first to second, and the RPM at which second gear is engaged (usually very close to redline), combined with the sudden instantaneous acceleration and incredible grip that car has. 2nd gear will naturally fail before any other. 3rd being the next most likely, and thus declining as you go on. How many people have ever blown out 5th gear. Their is just not enough acceleration associated with going from 4th to 5th to load up that gear. 2nd gear however is hit hard, and hit often.

Whether this actually addresses this post, well probably not. But I have had this on my mind for a short while now, and wanted to write it somewhere. <IMG SRC="http://www.i-club.com/ubb-files/smilies/biggrin.gif" border=0>

have a great day!
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Old 02-22-2001, 06:17 PM   #20
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Didn't Shiv break 5th gear?
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Old 02-22-2001, 06:35 PM   #21
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FWIW
Excellent swords are differentially tempered 52 rockwell on the edge, and 48 in the center.

Considering a gear set is more spendy than a auto tranny, maybe if anyone ever comes up with paddle shifters for the auto, Ill go that way and convert to f1 style rather than get new gears.
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Old 02-22-2001, 07:48 PM   #22
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I thought shiv broke 4th, but it was due to a manufacturer's flaw, not abuse.
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Old 02-26-2001, 03:55 PM   #23
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Any luck on the salvages parts Dan_E?

-Jon
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Old 02-26-2001, 07:44 PM   #24
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Does anyone have the gear ratios for the Legacy tranny in question?

If I could get a stronger tranny AND not have to shift into third to hit 60...



Aaron
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Old 02-26-2001, 07:57 PM   #25
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I try to make smooth consistant shifts in and out of 2nd. You can feel when you do it right and wrong. There is a resistance when the gear is still loaded.
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