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'98 2.5 RS
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Discussion Starter · #1 ·
last time i had my car off all 4s; is spun both front and rear wheels. the fronts spun in the same direction and the rear wheels spun in opposite directions. doesnt this mean i have a LSD in the front and open diff in the rear?

this is why i ask:
"Putting that extra grunt down to the road, is Subaru's famous full-time all-wheel-drive system. Starting with either a 5-speed manual transmission or 4-speed automatic, Subaru uses a center differential for primary torque split. An open front differential is used on all models, with an open rear diff used through 1999, and a limited-slip rear diff on 2000 and later models. That rear differential is the venerable Hitachi R160, used for years in cars such as the Datsun 510" - http://www.rs25.com/forums/showthread.php?t=20985&page=1&pp=15
 

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2017 WRB BRZ w/PP
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LSD = wheels turn opposite when spun. This is caused by the spider gears inside the diff. Google an image of diff to see what I mean.

Open Diff = Wheels spin the same way when spun
 

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Premium Member
overdeveloped beater
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8,335 Posts
^^Not quite......and actually completely opposite of true.

An open diff will spin opposite directions. An LSD will usually spin the same direction, but it can turn opposite with some resistance.

To the OP, what were the rear wheels doing when you saw this?
 

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Meany Head
2000 RSC
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10,236 Posts
LSD = wheels turn opposite when spun. This is caused by the spider gears inside the diff. Google an image of diff to see what I mean.

Open Diff = Wheels spin the same way when spun
Uh... actually... not quite. The direction of the tire turning is not totally dependant on Open or LSD. All differentials "want" to act the same way. It depends on what type of "LSD" is in use. However, the trick to doing these tests though it to make sure your trans in in gear, or park. Because if your in neutral, then you've introduced a 2nd place for your torque to travel.

For simplicity, lets not focus on the Subaru system for a moment. Take a solid axle Chevy truck with an open diff. Put the back end in the air and here is what will happen.

- With an Open Diff and the Trans in Park. turn one tire, the other tire WILL turn the oposite direction.
- With a viscous coupling LSD and the trans in park, turn one tire, and... The other tire WILL turn the opposite direction. Yes, it will.
- With a clutch pack type of LSD like a Possi-Track system, and the trans in park, you might have a hell of a time turning that one wheel, if at all. Because the clutch pack is fighting you against the trans in park.
- With that clutch pack LSD and the trans in neutral, turn one tire, and the other tire will turn the SAME direction.

Now, introduce the AWD system of the Subaru. And you have to know what impact the center diff has on the system. This is why it's important to know what happens if your in gear or neutral.

So... to answer the OPs question... Were you in neutral or in gear? Because if you were in neutral, then turning the front tire could very easily turn the other the same way with an open diff.

And finally, here is the biggest gotcha. You can't test a VCLSD diff the same way you can test a Clutch Pack LSD. They don't operate the same. the clutch pack is ALWAYS resisting slippage, but the VC LSD only resists slippage after slipping has already gotten off to a good start. You can't emulate that kind of slippage with your hands.
 

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'98 2.5 RS
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763 Posts
Discussion Starter · #5 ·
the car was in neutral. so the answer to my question is if its a stock 98 then its open at both ends?
 

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Premium Member
'17 Impreza Sport, '15 OB 3.6R
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Skidd said:
Uh... actually... not quite.

...............................
No, not true....



"Diff" means "not the same" .....


n00bs...





:run:








:lol:
 

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Premium Member
overdeveloped beater
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8,335 Posts
I never use wikipedia....but it probably has some long winded explanation about the term differential. It should include some sort of history about how the term was originally used to describe the different path lengths of the inside and outside drive wheels.

It got muddied up from there......
 

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'98 2.5 RS
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Discussion Starter · #12 ·
so the next logical question is how hard is it to swap the my diff(s) for an OEM 00/01 diff(s)? and how much better are would an aftermarket unit be?
 

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'98 2.5 RS
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763 Posts
Discussion Starter · #13 ·
uhh, what diffs can i swap (ie. what years)? do the gear ratios front and rear need to be the same?

sorry to be such a noob. everyones got to be one at some point.
 

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02 GD6
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Uh... actually... not quite. The direction of the tire turning is not totally dependant on Open or LSD. All differentials "want" to act the same way. It depends on what type of "LSD" is in use. However, the trick to doing these tests though it to make sure your trans in in gear, or park. Because if your in neutral, then you've introduced a 2nd place for your torque to travel.

For simplicity, lets not focus on the Subaru system for a moment. Take a solid axle Chevy truck with an open diff. Put the back end in the air and here is what will happen.

- With an Open Diff and the Trans in Park. turn one tire, the other tire WILL turn the oposite direction.
- With a viscous coupling LSD and the trans in park, turn one tire, and... The other tire WILL turn the opposite direction. Yes, it will.
- With a clutch pack type of LSD like a Possi-Track system, and the trans in park, you might have a hell of a time turning that one wheel, if at all. Because the clutch pack is fighting you against the trans in park.
- With that clutch pack LSD and the trans in neutral, turn one tire, and the other tire will turn the SAME direction.

Now, introduce the AWD system of the Subaru. And you have to know what impact the center diff has on the system. This is why it's important to know what happens if your in gear or neutral.

So... to answer the OPs question... Were you in neutral or in gear? Because if you were in neutral, then turning the front tire could very easily turn the other the same way with an open diff.

And finally, here is the biggest gotcha. You can't test a VCLSD diff the same way you can test a Clutch Pack LSD. They don't operate the same. the clutch pack is ALWAYS resisting slippage, but the VC LSD only resists slippage after slipping has already gotten off to a good start. You can't emulate that kind of slippage with your hands.
this is very accurate and well put info. props, couldnt have done better.
 
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