Jump to content
Ultimate Subaru Message Board

Recommended Posts

There's a question that came up on alt.autos.subaru that can't seem to get resolved. I've always wondered this myself, but never asked:

 

In regards to the Sube's with the manual-trans AWD like the late 90's Outbacks & OBS, etc. (not WRX):

 

Does the engine drive both the front and rear axle mechanically through a center differential gearset which is paralleled with a viscous clutch,

 

OR:

 

Does the engine drive the front axle directly and drive the rear shaft through a viscous clutch?

 

Read it again. :D

Share this post


Link to post
Share on other sites

On the MT's. Power is transferred to the driven shaft, which then transfer power to the center diff where it's then transferred to the drive pinion shaft for the front and transfer drive gear for the rear.

 

So yeah, it drives both front and rear.

 

Here's a scan that might help

http://www.main.experiencetherave.com:8080/subaru_manual_scans/FSM_Scans/AWDMT_description.jpg

Share this post


Link to post
Share on other sites

Thanks Josh, I've studied the drawing. Do I correctly arrive at the conclusions:

 

1. The front is "hard-coupled" with no slippage?

 

2. The rear is subject to the amount of slippage that the viscous unit will allow?

Share this post


Link to post
Share on other sites

No they are tied together.

 

It get's a little complicated to explain, but I'll do my best.

 

The big thing most people don't see is that the drive pinion shaft runs through the center of the driven shaft. They both are splined and input into the center diff.

 

Rather then me try to explain this in a million words. Check out these scans

 

Drive pinion & driven shaft. You can see that one goes inside the other

http://www.main.experiencetherave.com:8080/subaru_manual_scans/FSM_Scans/MT_AWD_drive_pinion_assy.jpg

 

Description of the center diff & awd system

http://www.main.experiencetherave.com:8080/subaru_manual_scans/FSM_Scans/MT_centerdiff1.jpg

http://www.main.experiencetherave.com:8080/subaru_manual_scans/FSM_Scans/MT_centerdiff2.jpg

http://www.main.experiencetherave.com:8080/subaru_manual_scans/FSM_Scans/MT_centerdiff3.jpg

Share this post


Link to post
Share on other sites

I did not realize that the VC acted on a mechanical center diff. I thought the VC was the center diff.

 

No wonder this system works so well :D

Share this post


Link to post
Share on other sites
Rather then me try to explain this in a million words. Check out these scans

Those detailed views did the trick. Thanks Josh.

Share this post


Link to post
Share on other sites
I did not realize that the VC acted on a mechanical center diff. I thought the VC was the center diff.

 

No wonder this system works so well :D

Yeah, just a good ol' fashioned diff like on an axle. One input and two outputs. Then a limited slip tied across the outputs.

 

Interesting thing I learned from the description is that the plates in the viscous unit actually come in contact with each other when activated. Previously I'd thought that the action was strictly a thickening of the silicone fluid.

 

to wit:

 

"As differential action continues, internal pressure will abruptly increase so that inner and outer plates (alternately arranged) come into contact."

Share this post


Link to post
Share on other sites

Exactly. The textbook definition of "overloaded differential" is wheelspin at one end (not to be confused with overloaded limited slip clutch, which is described as damage caused by overheat and overpressure causing the silicone contents blowing out past the seals).

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

×