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1996 Subaru Legacy Outback 2.2L AT
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Discussion Starter #1
I just picked up a rear end for a 2004 Outback 3.0 non-vdc thats supposed to be a LSD, but i can see the spider gear bar down in there. The bar isn't round though, its more triangle shaped. I thought LSD rear ends you could push a broom stick through both sides
 

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03 H6 OBW & 06 WRX Sportwagon
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DIY-Turbo 2.2l OBS 12.89s 1/4mile @ 106.17MPH
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it's gonna be viscous if it's LSD (likley) but, folks say the 'LS' function is worn out after about 60k -dunno.

links that might help; http://www.subaruoutback.org/forums/110-gen-2-2000-2004/30800-limited-slip-diffs.html

How to Identify Rear Differential - Subaru Impreza GC8 & RS Forum & Community: RS25.com

my wife's 03 H6 with weather package spins both rear tires the same direction.
When I went LSD hunting for my '03 Legacy L-SE I had a list of years with LSDs & basically checked that both rear wheels spun in the same direction (I've seen V-lsd cars wheels not spin in the same direction in the past - ? if the V-LSD was dead) - I wound up with a diff out of a 4eat Outback that I gutted for use in my 3.9FD case.

Newer Subaru V-LSDs look like an open diff, but the flange the ring gear bolts onto has two 1/2's & the spider gears have finer teeth than open diffs.

There is a "LSD conversion" how to thread on RS25 with pics.
 

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03 H6 OBW & 06 WRX Sportwagon
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(I've seen V-lsd cars wheels not spin in the same direction in the past - ? if the V-LSD was dead)
ah, good to know, maybe our OB still has it's diff working.

one thing tha is weird, supposedly my 06 wrx wagon came with rear lsd, but it's wheels spin the same way last I checked. But, not sure I had the mt in neutral if that matters.
 

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Yes, it does matter. If the prop shaft can't turn, and one rear wheel can be manually rotated, the other wheel HAS TO turn in the opposite direction. This applies with a LSD or open differential. That's because the ring, or crown, gear can't turn -- it's engaged through the pinion gear to the fixed prop shaft.

With an intact V-LSD, turning one wheel manually with the prop shaft fixed will be much more difficult than trying the same at the front. At the front, one wheel can probably be turned fairly quickly, and if spun fast it will continue to turn for at least a 1/2 turn. But with V-LSD, as soon as your hand is off the wheel, it stops.

When the prop shaft is free to turn, the friction of the drive shaft etc is less than the friction of the viscous coupler seals inside the differential. The seals are able to drag the other axle in the same direction. because the crown gear can now rotate.

This "test" only confirms the likelihood the differential is V-LSD. It's based on the friction of the seals. If the seals are badly worn, the wheel can be spun more easily. But, if the seals are worn, it's likely the special fluid in the viscous coupler has probably leaked out and the coupler isn't working. Similarly, even if the seals appear to be intact, it's still possible for there to have been some mixing of fluids, rendering the coupler ineffective.

According to the Identification section of my 07 FSM, the differential is supposed to have a label on the side, however, it didn't. I also checked a number of others in my dealers service department and they were all the same -- no label.
 

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2011 Tacoma TRD Sport Double Cab Long Box
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my wife's 03 H6 with weather package spins both rear tires the same direction.
Same with my '04 LL Bean, and mine still works. Got it high centered once and if I jacked a rear wheel up and put a large rock under it, that wheel would get enough power to move me backwards. The other wheel was in the air. Tried it on some ice last winter and discovered that it still seems capable of transferring power side-to-side in the rear in those conditions too.

With an intact V-LSD, turning one wheel manually with the prop shaft fixed will be much more difficult than trying the same at the front. At the front, one wheel can probably be turned fairly quickly, and if spun fast it will continue to turn for at least a 1/2 turn. But with V-LSD, as soon as your hand is off the wheel, it stops.
Makes sense, last time I had both rear wheels jacked up I did find they were difficult to turn and you couldn't really get them to spin without using constant force.
 

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1996 Subaru Legacy Outback 2.2L AT
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Discussion Starter #8
i had them pull a 98 forester axle while i was there so i could make sure it fit. it went in and i turned the axle by hand, and with my other finger i felt the other side splines spin in the same direction but the output shaft was also spinning so i dont know what that proved. then i thought back, shouldnt that axle have snapped in to the c-clip. i cant remember in detail if i pushed it in all the way, perhaps i didnt but it felt natural so maybe i just didnt care to notice.
 

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Same with my '04 LL Bean, and mine still works. Got it high centered once and if I jacked a rear wheel up and put a large rock under it, that wheel would get enough power to move me backwards. The other wheel was in the air. Tried it on some ice last winter and discovered that it still seems capable of transferring power side-to-side in the rear in those conditions too.



Makes sense, last time I had both rear wheels jacked up I did find they were difficult to turn and you couldn't really get them to spin without using constant force.
her Outback def. has drag - enough to kinda make it difficult to adjust the parking brake star and know when it begins to drag.
 

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1996 Subaru Legacy Outback 2.2L AT
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Discussion Starter #10
well i pulled the rear cover and found this, sure looks like an open diff to me

 

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1996 Subaru Legacy Outback 2.2L AT
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Discussion Starter #11
seems i spoke too soon. I finally found a very useful link, very suprised how similar they are. according to this, i do have a LSD

LSD vs Open guts
 

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Wow, subtle difference! So when the LSDs go, it's because the clutch plates have worn out?

I wonder how much more expensive the LSD is to produce...doesn't look like it could be all that much worse. Makes you wonder why Subaru didn't put it in everything that didn't have VDC.
 

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Discussion Starter #13
No clutches. Its a fluid based coupling sort of like the torque converter in an automatic transmission, but the fluid in a vlsd is silicone based and thickens up as its heated. The coupling I beleive is attached to the smaller gear that the axle slides into inside the ring gear. The coupling tries to keep that smaller gear and the ring gear spinning at the same speed, when slippage occurs the fluid heats up and start the "effect". Once the smaller gear and ring gear are spinning the same speed again, the spider gears can then tranfer the power to both wheels evenly. This all happens in split seconds
 

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Great pics, and link! Thanks.

Wow, subtle difference! So when the LSDs go, it's because the clutch plates have worn out? . . .
The plates themselves are not in contact with each other (at least they're not supposed to be), so normally they don't wear out. However, the plates are very close to each other and are perforated. There's a special viscous fluid between the plates. Alternating plates are attached to one side gear and to the differential case. When they turn at different speeds, which happens when one wheel spins relative to the other, the fluid between the plates heats up due to the "shearing" effect between the plates. As a result, the fluid "gels". Because the gelled fluid is not only between the plates but through the perforations, when it becomes stiff it resists the relative movement of the alternating plates.

I believe the most common failure in the V-LSD is the seals, which separate the plate area from the rest of the differential. (It's that extended "housing" to the left of the crown gear in the pics.) Once the seals go, and the viscous fluid either leaks out, or becomes mixed with the gear oil in the differential, the gelling effect is lost. Loss or mixing of fluid could happen very slowly over a long time. The seals might still cause the drag that leads to both wheels turning in the same direction when manually rotated, but the LSD won't be effective.

See also the attached description from my 2007 FSM, and http://en.wikipedia.org/wiki/Viscous_coupling_unit, which has photos of the plates (not Subaru LSD but essentially the same idea).

(p.s., woops, see I doubled with no64terry).
 

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1996 Subaru Legacy Outback 2.2L AT
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Discussion Starter #15
Other than the bushing bolts, the swap was painless. Axles clicked right in but wont be able to test it until I put the motor back in.
 
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