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98 Legacy OB diff questions


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5 replies to this topic

#1 grinderdust

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Posted 27 December 2012 - 08:45 PM

Greetings all from snowy central PA, It's been a long time since I've been here working on my old Brat. After a day spent fussing with my snowthrower, my thoughts turn to rebuilding some things on my Soob next spring. My main concern is winter traction as I like to ski and drive in deep snow. My car is a 5 speed and I'm told it has three diffs instead of a traction control cpu. I am curious to know if the differentials are sealed separately from the drive gears and if anyone knows if they can be filled with a thicker silicone grease like the ones on radio controlled race cars. These cars can be tuned for a good balance between forward traction and tight turning by changing the thickness of the grease. Does the Soob have oil filled gear diffs? Are they a limited slip type? I seem to be getting more spin than I'd like, even with the most aggressive tires I can find. Don't get me wrong the car is amazing. I'm just wondering if it could be even more so.

#2 grossgary

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Posted 27 December 2012 - 10:05 PM

A manual trans AWD or 4WD Subaru does have 3 differentials.

The front differentials are all open differentials with very rare exceptions that you would know because of an enormous price tag. The front differentials are also integrated with the transmission and are essentially a one piece unit with the trans.

* you can get locking front diffs (various types - helical, etc). mostly due to setting of the backlash very few people do it.

The center differential is integrated into the transmission and is a viscous limited slip type. I believe iIvans Imports (user name) has been rebuilding them, find his recent thread or start a new one to get his attention and PM him to reply to it. Now that I say this...i'm wondering if he's rebuilding the centers or the rears...

The center differentials are sealed units (as you seem to be familiar with - cool, please take on this project!!!). They can be removed from the transmission from under the car without removing the transmission so it's not that large of a job actually. The changing of fluid is beyond me but I like what you're saying, that's cool stuff. presslab (user name - i think it was him anyway) did this with struts, drained and filled them with new and thicker oil with good results. But that is way beyond me.

Rear differentials are either open or VLSD (viscous limisted slip). www.cars101.com has all the options and what came stock with a vehicle. The rear viscous limited slips wear out though and essentially operate like an open diff, so having one or installing one doesn't necessarily mean much.

Some older Subaru's (1980's stuff) come with clutch type rear differentials which are always locked until they reach a certain preset load and then they give (so they are forgiving as needed around turns). I prefer those types myself for snow and light traction needs I have, they are always locked, but they're harder to find.

#3 Gloyale

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Posted 30 December 2012 - 01:56 PM

Rear differentials are either open or VLSD (viscous limisted slip). www.cars101.com has all the options and what came stock with a vehicle. The rear viscous limited slips wear out though and essentially operate like an open diff, so having one or installing one doesn't necessarily mean much.


The VLSDs work EXCELLENT for snow.

And FWIW, I've seen as many fail to "locked" as I have seen fail to "open" states. Even the Center VLSD can fail to locked.....yes, manuals do get torque bind sometimes.

#4 grossgary

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Posted 30 December 2012 - 03:00 PM

The VLSDs work EXCELLENT for snow.

Was only talking about a failed rear differential. No mention of properly working VLSD's or center diffs.

And FWIW, I've seen as many fail to "locked" as I have seen fail to "open" states. Even the Center VLSD can fail to locked.....yes, manuals do get torque bind sometimes.

Right, wasn't talking center diffs, though torque bind due to MT VLSD failure is common, I've seen that too.

Have you seen ***rear*** VLSD's fail to "locked"? I've never seen that.

I've only seen MT center diff's fail locked.

#5 Gloyale

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Posted 30 December 2012 - 03:29 PM

Have you seen ***rear*** VLSD's fail to "locked"? I've never seen that.



Yes I have. VLSD installed on a 90 Legacy, 3in lift, 235/75/15 tires through a D/R 5spd. One would swear it's welded when you see that car wheel. Chirps rear tires a hair in dry parking lots.

#6 pamike

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Posted 30 December 2012 - 10:44 PM

Greetings all from snowy central PA, It's been a long time since I've been here working on my old Brat. After a day spent fussing with my snowthrower, my thoughts turn to rebuilding some things on my Soob next spring. My main concern is winter traction as I like to ski and drive in deep snow. My car is a 5 speed and I'm told it has three diffs instead of a traction control cpu. I am curious to know if the differentials are sealed separately from the drive gears and if anyone knows if they can be filled with a thicker silicone grease like the ones on radio controlled race cars. These cars can be tuned for a good balance between forward traction and tight turning by changing the thickness of the grease. Does the Soob have oil filled gear diffs? Are they a limited slip type? I seem to be getting more spin than I'd like, even with the most aggressive tires I can find. Don't get me wrong the car is amazing. I'm just wondering if it could be even more so.


get snow tires, makes a big difference. i run the general altimax arctic's on my wrx. also a small lift for more clearance helps




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