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Front diff interchangeability: The true answer


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181 replies to this topic

#1 WJM

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Posted 21 December 2005 - 04:39 PM

38421AA020

Application(s):
DL/GL/GL10/RX/XT/XT6/Leone/Loyale 4wd and 4wd TURBO 5MT S/R+D/R(read: ALL ea82/ER27 4wd and 4wd turbo S/R+D/R transmissions)
ALL Legacy 4wd 5spd to 2004MY
ALL Baja N/A 5spd to 2003 MY
ALL Impreza 5spd to 11/2003 production date (including ALL WRX and STi 5spd, except 6MT)
ALL Forester 5spd to 2003 MY

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They are the SAME unit from 1984(1985 MY) to 2003(2004MY, however some are mixed with the new type stubless driff) for all 4WD 5spd transmissions.

Guess what that means? We have had nearly unlimited front LSD options ever since companies started making fornt LSDs for the 5spd.

OBX-R Helical for me.

#2 Numbchux

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Posted 21 December 2005 - 04:55 PM

I thought the consensus was no....but that little winking smiley makes me suspect otherwise....

did you find a way to lower your final drive?!

#3 WJM

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Posted 21 December 2005 - 10:54 PM

final drive is not of my concern.

#4 WoodsWagon

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Posted 21 December 2005 - 11:00 PM

he want an acid fix for the front end.

#5 WJM

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Posted 22 December 2005 - 10:55 PM

bump for truth.

#6 All_talk

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Posted 22 December 2005 - 11:14 PM

So just to be completely clear.... I can put a EJ limited slip front diff in my EA box?

And... How did we not know this before now?

Gary

#7 LPGsuperchargedBrumby

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Posted 22 December 2005 - 11:25 PM

does the 4spd D/R diff interchange with 5spd diff?
as a LSD in the front of the Brumby would rock on gravel

#8 All_talk

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Posted 22 December 2005 - 11:38 PM

And what are our LSD choices from the EJ apps...

VLSD?
Clutch type?
WRX "gear" type?

Gary

#9 spanky_pete

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Posted 22 December 2005 - 11:44 PM

As if I didn't have enough projects already, now it looks like I might be pulling that XT6 AWD d/r tranny I have out of storage this spring. :grin:

Nice find.

#10 Caboobaroo

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Posted 23 December 2005 - 12:21 AM

very nice Will. I think I have another FT4wd RX tranny somewhere that I could swap an LSD into for it

#11 torxxx

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Posted 23 December 2005 - 01:25 AM

Wait wait wait so what do I need to make my front end LSD? a legacy LSD?

#12 WJM

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Posted 23 December 2005 - 07:45 AM

So just to be completely clear.... I can put a EJ limited slip front diff in my EA box?

And... How did we not know this before now?

Gary


as long as it is a 4WD 5spd box, yes.

How? people dont think like I do.

SUBARUs=Legos

does the 4spd D/R diff interchange with 5spd diff?
as a LSD in the front of the Brumby would rock on gravel


I do not know that. Someone will have to pull a 4spd apart and compare the diffs. The partnumber is different, and the stub spline count is different...which makes me think no...however, it very well could be the same.

And what are our LSD choices from the EJ apps...

VLSD?
Clutch type?
WRX "gear" type?

Gary


Clutch.
Helical.
SureTrac.
VLSD.
Open.
*insert all other brand names here*

Wait wait wait so what do I need to make my front end LSD? a legacy LSD?


You will need a FRONT LSD to be installed. ANY REAR LSD will NOT work. See my other thread about that.

#13 operose

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Posted 23 December 2005 - 08:37 AM

sweet.


I already have the transmission out of the xt6. where's a reputable place to get a front LSD?

#14 Numbchux

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Posted 23 December 2005 - 09:58 AM

so the carrier's the same...but the ring/pinion are different (EA vs. EJ)

#15 WJM

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Posted 23 December 2005 - 10:12 AM

Pinion is. Rings are not as long as they are the same ration. aka 3.900 ring to 3.900 ring......3.700 ring to 3.700 ring........................

IF you can find an old school pinion for the transmission thats 4.444...then you can get a new school ring thats 4.444...

I know the pinion shafts *LOOK* very different and are only avalible in 3.700 and 3.900....so...........

BUT...I've not fully dissasembled the old school pinion shaft section YET.

#16 grossgary

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Posted 23 December 2005 - 10:23 AM

awesome will, excellent work.
now...i can't believe noone else is asking this...am i that stupid? i've done alot of work on subaru's but noone else is wondering....what all is involved in swapping an LSD front diff into an EA (or ER) series? i've never taken apart a transmission before.

how hard is the swap?

#17 WJM

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Posted 23 December 2005 - 10:42 AM

Dude, its easy....the same as swapping it into anyother 5spd subie transmission.

#18 Adam N.D.J.

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Posted 23 December 2005 - 11:19 AM

does the 4spd D/R diff interchange with 5spd diff?
as a LSD in the front of the Brumby would rock on gravel


4spd diff is different. It's smaller than the 5spds. As WJM said, as long as you have a 5spd, your good, 4's won't work.


The pinion in the old school tranny's isn't different from 3.900 to 3.700, I've torn apart 3 tranny's now, two 3.900 and a 3.700 all three had a 10 tooth pinion gear, the difference was in the ring gear the 3.700 has 37 teeth, and the 3.900 has 39. I've never torn into a new tranny. But if they hold true to the EA's then we are in luck. Cause if the Legacy has a 10 tooth pinion gear, and 41 tooth ring gear, we can drop that bad boy into an EA 5spd D/r and lower gears for the offroad world.

However I have not personally had the pleasure of taking apart an EJ tranny, so I'm not entirely sure of this.

I am thinking that the pinion gear's would have to be different for a 4.111 or 4.444, cause if you have a 9 tooth pinion on a 37 tooth ring gear you get 4.111, and a 40 tooth ring you get 4.444. But the difference in that one tooth would make the rings useless in our diffs, as they wouldn't mesh.

on the other hand. . . hmmm. . . . back to the lab!

#19 operose

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Posted 23 December 2005 - 11:26 AM

Dude, its easy....the same as swapping it into anyother 5spd subie transmission.


what he's saying is that he's never taken a transmission apart... me either... and this is a good question.. what's involved in getting the old diff out/ new diff in once you have the transmission out of the car?

#20 Sweet82

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Posted 23 December 2005 - 11:32 AM

With a welded diff on an EA series....Would you really notice the added benefit?

#21 WJM

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Posted 23 December 2005 - 11:57 AM

what he's saying is that he's never taken a transmission apart... me either... and this is a good question.. what's involved in getting the old diff out/ new diff in once you have the transmission out of the car?


Oh...I would NOT recommend taking one apart if you plan on making it work again. The S/R EJ trans seemed rather simple...the D/R with diff lock was...more complicated. All kinds of things fell out that I have no idea where they came from....however I am going to attempt to put it back together with the Helical in it and BEAT THE EVER LIVING SHIZZZZZZZZZZZZZNIT out of it to find thse transmission's TRUE limits.

As for weling...I wouldnt recommend a welded front. Do a clutch type front atleast...for offroading...

#22 operose

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Posted 23 December 2005 - 12:25 PM

Oh...I would NOT recommend taking one apart if you plan on making it work again. The S/R EJ trans seemed rather simple...the D/R with diff lock was...more complicated. All kinds of things fell out that I have no idea where they came from....however I am going to attempt to put it back together with the Helical in it and BEAT THE EVER LIVING SHIZZZZZZZZZZZZZNIT out of it to find thse transmission's TRUE limits.

As for weling...I wouldnt recommend a welded front. Do a clutch type front atleast...for offroading...


what would you suggest for my single range 5spd in my xt6.. for general street / mild offroad?

is it going to be a real PITA to swap a new front diff into this transmission do you think?

sorry for questions, don't have FSM with me at work

#23 All_talk

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Posted 23 December 2005 - 12:25 PM

The pinion in the old school tranny's isn't different from 3.900 to 3.700, I've torn apart 3 tranny's now, two 3.900 and a 3.700 all three had a 10 tooth pinion gear, the difference was in the ring gear the 3.700 has 37 teeth, and the 3.900 has 39. I've never torn into a new tranny. But if they hold true to the EA's then we are in luck. Cause if the Legacy has a 10 tooth pinion gear, and 41 tooth ring gear, we can drop that bad boy into an EA 5spd D/r and lower gears for the offroad world.

However I have not personally had the pleasure of taking apart an EJ tranny, so I'm not entirely sure of this.

I am thinking that the pinion gear's would have to be different for a 4.111 or 4.444, cause if you have a 9 tooth pinion on a 37 tooth ring gear you get 4.111, and a 40 tooth ring you get 4.444. But the difference in that one tooth would make the rings useless in our diffs, as they wouldn't mesh.


Its not as simple as tooth count, the gear geometry is different between the ratios, without getting into the engineering, the ratios come down to pitch diameters, not tooth count. You can not mix and match ring and pinion gears in a hypoid set (or any bevel set for that matter).

Gary

#24 All_talk

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Posted 23 December 2005 - 12:30 PM

And.... Gear setup is VERY critical, you cant just swap them. Adjusting the placement and backlash is not an easy task for a novice mechanic. And if not done correctly the gear set will chew its self to bits in very short order!

Just be for warned
Gary

:(..... I hate being a buzz kill

#25 operose

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Posted 23 December 2005 - 12:36 PM

And.... Gear setup is VERY critical, you cant just swap them. Adjusting the placement and backlash is not an easy task for a novice mechanic. And if not done correctly the gear set will chew its self to bits in very short order!

Just be for warned
Gary

:(..... I hate being a buzz kill




so is that a "don't try this at home kids" ?




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