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base model awd vs 4wd


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#1 pwjm

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Posted 14 November 2011 - 05:49 PM

When comparing Loyal's (4wd) with legacy and impreza's (awd)...

how do the awd systems of the early 90's work. since most models didn't have any special diffs in them, was it pretty much just power to one wheel, but it could go to any wheel.


I understand that most 4wd systems guarantee that at least 2 wheels (1 front and 1 back) get power to them.

if anyone can help clear this up, it'd be greatly appreciated.

#2 MilesFox

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Posted 14 November 2011 - 06:36 PM

in a gl, you have a front and rear opern differential. in a pushbutton, or dual range, you hae a pto gear that directly engages the rear diff from the front diff.

So the front and rear are essentially locked together, but any one wheel on bot the front and back diff will be engaged to each other, either same side, or diagonal. If only the front or rear wheels were on the ground, one wheel will have traction, one in the air would be engaged to it. If the car had both wheels on one side in the air, it goes no where.

There are gl's and rx with lockable open center diffs, and rear lsd. the rear lsd's are clutch type.

But with this setup, all the power can go to either the front diff, or the rear, and will spin out whatever wheel has the least traction. With a rear LSD, all the power can go the one front wheel. When the diff is locked, it behaves like a regular 4wd.

The 'awd' impreza and legacy have a viscous center diff. at slow speeds, it will act as an open diff. When there is a difference in rotation across the front and rear diffs through the center, the fluids heat up and cause the mechanism to engage, locking the front and rear diff back together, until the rotation of the front and rear diffs are matched through the center.

In a 3at trans, there is no center diff, and the rear is driven by an electric solenoid to engage clutches.

the 4eat is similar, the the trans control unit engages the clutches whenever there is a difference in rotation, but can release it while making turning maneuvers, and is a balance of this.

#3 pwjm

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Posted 14 November 2011 - 07:14 PM

The 'awd' impreza and legacy have a viscous center diff. at slow speeds, it will act as an open diff.


Thanks for the info!

It's been my experience with VLSD's that they tend to stop working fairly early in their life and don't take abuse well. At least in my nissan and a buddies miata. For my nissan, it's actually not something you can repair as it's a sealed unit.

#4 987687

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Posted 14 November 2011 - 07:23 PM

Thanks for the info!

It's been my experience with VLSD's that they tend to stop working fairly early in their life and don't take abuse well. At least in my nissan and a buddies miata. For my nissan, it's actually not something you can repair as it's a sealed unit.


Unlike most rear diffs, the vlsd in the center of the 5speeds fail to locked up not open.
And they don't fail terribly often.




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