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Guest trbharris

AWD Technical Description

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Guest trbharris

I would like a detailed TECHNICAL description on how the Outback AWD works. Any pointers to an article would be very helpful.

 

Thanks!

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Guest Legacy777

Actually....that only describes the manual trannys.

 

Since you have an Outback, you most likely have an auto.

 

Here's a blurb from the factory manuals on the rear portion of the transmission that handles the AWD.

 

Essentially what happens is that there is a speed sensor on the rear drive shaft. There's also one on the front drive shaft. The computer monitors these for differences.

 

With like all auto trannys, they use hydraulic pressure to pretty much do any and all work in the tranny. Under normal driving conditions the computer gives a 90/10 front to rear torque split. It does this by altering duty cylce on the duty C solenoid in the rear extension housing. This solenoid controls how much hydraulic line pressure the rear clucth pack sees. By doing this it in essence can control how much power is going to the rear of the car.

 

So how it all works is when the computer detects a difference in speed sensors, it will alter the duty cylce on the duty C solenoid creating more hydraulic pressure going to the rear clutch packs, and allowing more power to be given to the rear wheels.

 

The most power split you can have with an auto is 50/50.

 

Contrary to Subaru's commercials.....the computer does not "take away" power from the front wheels if they are slipping. It merely adds more power to the rear.

 

The description above aplies to all subie autos except the VTD (Variable Torque Distribution) models. The VTD trannies are only found on the legacies with the H6 motor, and the new WRX. I'm sure subaru will start incorporating the new VTD trannies into all their models....but I think as of now those models are the ones to have it.

 

Oh....here are the scans from the Factory manuals.

 

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www.main.experiencetherav...ystem2.jpg

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Guest rcoaster

<blockquote><strong><em>Quote:</em></strong><hr>

The description above aplies to all subie autos except the VTD (Variable Torque Distribution) models. The VTD trannies are only found on the legacies with the H6 motor, and the new WRX. I'm sure subaru will start incorporating the new VTD trannies into all their models....but I think as of now those models are the ones to have it.

 

Actually, the 2003 Legacy GT now has VTD as well.

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Guest rcoaster

Nope.

 

VDC is a more advanced version of VTD. VTD has a planetary center differental, and gives you that 45% front / 55% rear power distribution under normal driving conditions.

 

VDC adds engine and braking control to the VTD system, giving you more stability while driving.

 

There are about 4 different kinds of system in Subaru's All wheel drive system. You can look up on Subaru's website that explains them in detail. They are:

 

1. viscous coupling center differental in manual transmission

 

2. Active all-wheel-drive in automatics (gives you 90/10 power split in normal driving conditions)

 

3. Variable Torque Distribution found in WRX's, and the Legacy GT.

 

4. Vechile Dynamics Control in the Outback H6 VDC.

 

-RC.

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Guest synapse79

josh, have a question about this,

"Contrary to Subaru's commercials.....the computer does not "take away" power from the front wheels if they are slipping"

 

do new subarus have any kind of traction control system that would apply the brake to a tire the tire that is slipping?

 

i wasnt sure, thought i would ask

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Guest Legacy777

synapse.....

 

The only system on subaru's that have anything similar to this is the VDC.

 

It is a true traction control system that can take power away from the engine to limit wheel spin if all four wheels are spinning.

 

I'm pretty sure it can brake individual wheels to transfer power side to side.

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