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Old 12-05-2013, 11:22 PM   #1
vicious_fishes
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Member#: 158864
Join Date: Sep 2007
Location: Aussieland
Vehicle:
2003 GD w/EZ30D swap

Default swapping input shafts? (4.11 to 3.7 FD)

i just did an H6 swap and my existing 2.5RS box is far too short for the EZ30. I figure if i just swap in a taller input shaft and a different diff i should be golden.

fairly easy to do? been done before? anywhere i can get the shaft without going to the stealership?
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Last edited by vicious_fishes; 12-06-2013 at 03:43 PM.
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Old 12-06-2013, 08:48 AM   #2
JarHarms
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Chapter/Region: MWSOC
Location: DeKalb-ish, IL
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06 WRX Ltd SGM 6MT
02 Forester S

Default

Pinion shaft. That with a corresponding ring gear of a different fd ratio is what you are looking at. The pinion shaft will need shim adjustment to set pinion depth and the ring gear will need side retainer adjustment to set backlash and bearing preload. You will need an FSM and some special tools.
Not sure if it can be described as easy but it has been done before. Parts are probably best to get at a dealer.

I would also price out and compare what a competent Subaru trans rebuilder would charge for parts and labor.
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Old 12-06-2013, 09:09 AM   #3
CNY_Dave
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I'm guessing your trans has 4.44 gears. Can you get anything taller than 4.11?

If you just need better highway legs, is there a taller OD you can put in the trans?
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Old 12-06-2013, 10:49 AM   #4
vicious_fishes
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2003 GD w/EZ30D swap

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Quote:
Originally Posted by CNY_Dave View Post
I'm guessing your trans has 4.44 gears. Can you get anything taller than 4.11?

If you just need better highway legs, is there a taller OD you can put in the trans?
it's 4.11 with 0.78 5th gear. the gearbox also has the problem of having fairly close 1-2-3-4 and then quite a large jump to 5th... but 5th is still far too short. 3080rpm @ 100km/h. 4th tops out at about 100mph at 6250rpm. 5th then jumps to about 225km/h at 6250. it's a very large jump to a gear that's just far too short anyway. 70mph highway is over 3300rpm and the H6 probably only needs 2500 at that speed.

ideally i'd just drop an 06-07 3.7FD box in but unless i get one of those shipped over from the 'states, they don't exist here. i'm also unsure about the LHD to RHD points on the shifter being the same.

considering the already huge jump from 4th to 5th, an even taller 5th would just be madness. i'd have to swap all the other gears as well and so it effectively just becomes a whole new gearbox but with extra labour to rebuild it all. swapping the necessary (pinion shaft/ring gear?) etc stuff up front makes much more sense.
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Old 12-06-2013, 11:01 AM   #5
CNY_Dave
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My H6 with a 4EAT has 4.11 gears (OD ratio 0.694?) and is turning about 2500 at 70. It doesn't see 3 grand until almost 80.

It runs pretty well on the freeway, so that's a decent target.
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Old 12-06-2013, 11:43 AM   #6
vicious_fishes
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2003 GD w/EZ30D swap

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Quote:
Originally Posted by CNY_Dave View Post
My H6 with a 4EAT has 4.11 gears (OD ratio 0.694?) and is turning about 2500 at 70. It doesn't see 3 grand until almost 80.

It runs pretty well on the freeway, so that's a decent target.
i have 5mt however.

and yes 2500ish was my target. 4.1 to 3.7 will drop revs by 10% which is a good improvement without putting in a whole new gearbox.

only alternatives in aussieland are either 4.11 wrx boxes with .738 5th gear (not worth bothering) or there are some 3.9 RA boxes (3.9 because they came with R180 rear diffs) but they have super short .972 or whatever 5th gears.

only really viable alternative to swapping the ring gear etc is the right 6 speed but that'll be much more expensive.
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