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Looking for info about what cars to find a 3.9 rear Limited Slip Differential of any type to fit a second gen Legacy.

Lets see if I got this right.

3.9 VLSD was available on early Legacy turbos. 91 was the only year reference I could find. Carrier is a direct swap, aside from mounting bolts/studs possibly? Axle differences?

 

3.7 clutch type LSD was available on mid and late 80's EA cars, but the guts can be swapped into a 3.9 R&P? I read something about a swap thread in the USRM, will check it out.

 

4.11 VLSD could be found in 02+ Impreza WRX. R&P/Case swap possible?

 

Some 00 or 01+ Legacy OB Limited had LSD option, but found no reference for ratios on those, probably 4.11?

 

Any other likely candidates to find a rear LSD unit in?

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You have the correct information so far. VLSD is not a true LSD if you are looking for that. Swapping the LSD from a 3.700 rear into a 3.9 or 4.1 is quite do-able. Write ups abound if you look hard enough.

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Unless you get one with very low miles - most used LSD's are going to be worn out. Especially the newer VLSD's. 50k is about their expected lifespan. The clutch types can be rebuilt but its not cheap.

 

Best bet is to get something with low miles from a newer WRX or legacy.

 

GD

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the vlsd was optional on the 00 or 01 outbacks, by 03 they were standard on the outbacks. (4.44 auto trans, 4.11 manual trans).

 

they were also on GTs in that era but i don't know the details. but cars101.com would tell you. or car-part.com will ask, locking or non-locking, if you search those years.

 

i understand lower mileage would be a safer bet for a used vlsd, but i question the 50k mile limit. the unit is not identical to the center diff vlsd, but it is the same design and those don't all die at 50k, do they? as a matter of fact, the center diff may get more wear and tear than the rear? maybe not.

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i understand lower mileage would be a safer bet for a used vlsd, but i question the 50k mile limit. the unit is not identical to the center diff vlsd, but it is the same design and those don't all die at 50k, do they?

 

they are different - the centers fail to "locked" the rears fail to "open" so operationally they must differ substantially since they fail in opposite ways. a few folks have mentioned seeing quite a few warn out LSD's, since they fail to "open", most folks would never really notice.

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There must be some different type of fluid in the rear VLSDs. Or different clearances maybe between the components inside the unit. I'm inclined to think it must have been designed to fail that way. If the rear diff locks when it fails the car gets "tail happy" on slick roads. Imagine the average Subaru driver trying to reel in a sideways slide in the rain...

 

I have read several times about the VLSD units failing at early mileage. It doesn't seem strange to me that the rear VLSD would wear out since the diff is constantly working when the car is in motion. Every turn, every curve, every time the crown of the road shifts, the differential is working to accommodate the change in wheel speed between left and right.

Too bad those units cost ~$600 new. If they were closer to $350 or $400 even, that would be a viable option.

 

I'm thinking the clutch type is probably the way to go, but assuming the clutches are worn, what would it cost to get new clutches/plates, and where would I buy them? Does a dealer still carry parts for cars that old?

 

 

DEA will be on this thread due to title ...
:D

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the clutch type ones seem to function fairly well even when old....haven't seen much info no rebuilding them, not sure how it works.

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the clutch type ones seem to function fairly well even when old....haven't seen much info no rebuilding them, not sure how it works.

http://www.gordon-glasgow.org/lsdtech.html

 

You also have to take the axle type into consideration. EA's and first gen legacys have female splines on the CV cups that go onto axle stubs sticking out of the diff.

 

Second gen legacys and newer have male splines on the axle that plug into the side of the diff. You can swap CV cups on to different axles to remedy that, but it's hit and miss on what fits.

 

The VLSD's are not very strong to start with, and it takes heat to warm them up and get them to lock up, so you have to spin a wheel for a bit before it really starts acting like a LSD. The clutch type ones are instant, and the harder you launch, the harder the clutches lock the wheels together.

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It's well-known in the Miata racing community that the VLSD's they are equipped with have a lifespan of about 50k miles. Give or take of course depending on the type of driving. Someone that commutes 50 miles a day on primarily straight, freeway type roads would get more - back-country roads with large numbers of tight turns would get less.... in real-world usage. If you are racing them they are good for one or maybe two seasons. They CANNOT be rebuilt and once toasted must be thrown away. Unless you have real numbers on their condition or mileage - I wouldn't pay the premium people usually ask for them. I have one with 170k on it in my '91 SS (factory equipped) and I can't even tell it's there - it's likely not doing anything at all.

 

You can test the breakaway torque of the clutch type units to determine their condtion and they can be rebuilt and adjusted. So not all is lost if you buy an older one.

 

GD

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http://www.gordon-glasgow.org/lsdtech.html

 

You also have to take the axle type into consideration. EA's and first gen legacys have female splines on the CV cups that go onto axle stubs sticking out of the diff.

 

Second gen legacys and newer have male splines on the axle that plug into the side of the diff. You can swap CV cups on to different axles to remedy that, but it's hit and miss on what fits.

 

The VLSD's are not very strong to start with, and it takes heat to warm them up and get them to lock up, so you have to spin a wheel for a bit before it really starts acting like a LSD. The clutch type ones are instant, and the harder you launch, the harder the clutches lock the wheels together.

can the differential and axles be swapped as a unit?

 

Specifically, can I remove my 1990 legacy open diff and axles (stub on diff) and replace it with an LSD diff and axles (stub on axle) from an RS?

 

Is there an issue with the RS axles in my legacy?

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