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Old 10-18-2003, 09:45 PM   #1
Scooby Newbie
Member#: 43114
Join Date: Sep 2003
Location: Pownal, VT
1998 Legacy GT Turbo

Default My Transmission Project

Well, my GT transmission decided to be stupid, so I'm beginning the long journey of a complete replacement, with a rebuilt, solid transmission.

Step 3 is complete, as I've found the replacement tranny and rear diff, and have begun dismantling it. This is a 97 Outback tranny and diff. The outside is a bit dirty and there's some rust, but the gears are looking pretty good, and none of them will need replacement. The full price was $500 from a salvage yard.

Step 2 will involve bringing the gears to a machinist to have them deburred.

Step 3 will involve me sending the gears and synchros to 300 Below for cryo treatment. This should really add some durability.

Step 4 Shotpeening. I'll bring these gears to a certified aircraft shotpeener for some shotpeening action.

Step X while all these things are going on, I'll be cleaning up the case and painting everything.

Step 5 Transmission installation!

Wish me luck on my journey, I have high hopes that this will create a truly formidable transmission setup, that'll hopefully never die.
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Old 10-19-2003, 01:59 AM   #2
Scooby Specialist
Member#: 40484
Join Date: Jul 2003
Chapter/Region: NWIC
Location: Salem, OR
'02 Murdered WRX
'02 Silver Legacy

Post Good Luck!

Well Good Luck buddy! I'm supportive of anyone who is trying to over come the Subaru's Achillies tendon (their tranny).

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Old 10-19-2003, 10:30 PM   #3
NASIOC Supporter
Member#: 30669
Join Date: Dec 2002
Chapter/Region: Tri-State
Location: USA, North NJ, 07456
1998 Legacy 2.5GT
Silver Sleeper BK, 5MT


Keep in mind that the OB 5th gear is worse for cruising than a GT 5th.

I can't remember about the others though. But, I could check if you want.
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Old 10-19-2003, 11:48 PM   #4
Scooby Specialist
Member#: 16653
Join Date: Mar 2002
Chapter/Region: NESIC
Location: Central MA
2012 Mazda 3
2013 Toyota Vanling


Shouldn't you shotpeen prior to cryo-treating?

From a materials standpoint, it just seems like it would be a better progression for the metal. But I am not a metallurgist, nor a tranny expert, so I could be mistaken.

Interesting process, though. If, in fact, you are supposed to cryo-treat and then shotpeen, I'd like to here the reasoning.

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Old 10-20-2003, 03:00 PM   #5
Scooby Specialist
Member#: 439
Join Date: Oct 1999
Chapter/Region: E. Canada
Location: yyz


I am curious how much hp your engine is putting out to require a special built transmission. Or this is required even for slightly modified engine.
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Old 10-20-2003, 03:31 PM   #6
MY99 2.5GT
Scooby Specialist
Member#: 5030
Join Date: Mar 2001
Chapter/Region: MAIC
Location: Martinsburg, WV, USA
1999 Legacy 2.5GT
12 Legacy GT 13 Armada


If your modifying for more then 300hp and similar torque your barking up the wrong tree

If you remember an article in SCC years ago about Shiv busting gears from a Dog Box in his turboed 2.5RS running almost 300 front wheel hp.

Its not gear strenght that is the issue with these transmissions. Unfortunitely the case itself is weak. If enough power/torque is transmitted to the input shaft of the trans it causes the case to flex and in turn seperates the gear teeth causing them to chip.

Best option would be to find a WRX trans and buy/fabricate a trans brace.

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Old 10-21-2003, 06:12 PM   #7
Scooby Newbie
Member#: 43114
Join Date: Sep 2003
Location: Pownal, VT
1998 Legacy GT Turbo


You're right, the shotpeening will go before the cryo, my bust.

I don't see myself going above 300 HP, though who knows what the future holds? I'm turboed right now, but i'm only running mild boost. If I plan on something huge in the future, I'm going to have to make a huge investment anyways.

My main concern is making a small investment now to have a long lasting transmission that I won't need to worry about for, hopefully, a long time. I say take the time and do it right.

The cryo treating process is a lot cheaper than I had thought before I made the initial phone call. It runs around $2.50/lb. They will do an entire 4 cylinder engine for $450. This process will work on just about anything, including turbo housing and axles.
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