[blueraja]

Hey guys,

Just wanted to share an experience I had this morning. Last night in central Ohio, we received some freezing rain. Having read recently that the 4 speed auto has a 50/50 torque split front to rear in first gear, I found a fresh, unsalted parking lot to ascertain the torque split. Let me just say that it is absolutely true! I had a great time fish tailing and controlled slides!

This was useful to learn just in case I got stuck and needed all the torque I could get. I now know that if this happens, first gear (and reverse) are the gears to use.




Sent from AutoGuide.com App

 

[RedGeminiPA]

My '01 VDC starts in 2nd gear if the selector is in 2nd. If anything, that would be the best to use, since it's not applying as much torque as 1st gear.

 

[plain OM]

You might have had some interesting reactions on the slippery surface, but, in fact, there is no fixed 50/50 split, regardless of gear. This was confirmed by measuring the actual signal that controls the transfer clutch under different conditions.

The clutch pressure is determined by a number of factors, such as throttle position, engine torque, gear, vehicle speed, and any difference between front and rear drive speeds. In first and second gear, the pressure on the clutch is more responsive to the variable factors than in the higher gears, but this is a far cry from the power being directed equally (50/50) to both the front and rear drives based solely on which gear is being used.

For more info on the measurements, have a look at the FreeSSM thread where we report the measurements in data and charts. (http://www.subaruoutback.org/forums...426-freessm-complete-access-your-ecm-tcu.html)

 

[CNY_Dave]

In 1 and 2 it is more responsive (quicker to kick in the AWD) than in 3 or D, and though more responsive it is not 'locked-in', as stated.

At idle (more specifically, throttle off) the AWD is basically disengaged.
Now, I can say there is a good reason for this after a recent experience.

Out of need (2004 trans does not work correctly in a 2003, long story) I have recently wired in a switch to disconnect the transfer solenoid from the TCU, and the switch can also 'lock' the AWD transfer clutch (so I can have AWD when I need it) by sending the solenoid a steady 12V (2004 is reversed, +12V for 100% duty cycle/maximal engagement, 0v for AWD disengaged).

Coming down a slick-as-owl-offal hill, with the AWD 'locked' (maximally engaged), I had something happen that has never happened before, the rear slid out under braking!

What was happening was that the rears were not generating proportionally less braking force as is proper, because the AWD clutch was 'locked' all 4 wheels were seeing the same braking force, but the front wheels had more traction, so the front wheels tracked and the rears slid.

This situation, though easily handled if you are careful, is sub-optimal.
There are good reasons to NOT lock the front to the rear.

 

[Wake]

At idle (more specifically, throttle off) the AWD is basically disengaged.

Is that why I feel a slight rumbling sensation when I first start rolling from a light? Kind of like knobby tire sensation? It's just for a second on initial take off.

 

[blueraja]

You might have had some interesting reactions on the slippery surface, but, in fact, there is no fixed 50/50 split, regardless of gear. This was confirmed by measuring the actual signal that controls the transfer clutch under different conditions.

The clutch pressure is determined by a number of factors, such as throttle position, engine torque, gear, vehicle speed, and any difference between front and rear drive speeds. In first and second gear, the pressure on the clutch is more responsive to the variable factors than in the higher gears, but this is a far cry from the power being directed equally (50/50) to both the front and rear drives based solely on which gear is being used.

For more info on the measurements, have a look at the FreeSSM thread where we report the measurements in data and charts.

Oh


Sent from AutoGuide.com App

 

[Novablue]

By the way Blue this is the reason they are saying that.


http://www.subaruoutback.org/forums...-freessm-complete-access-your-ecm-tcu-16.html

It's a very long read, but very informative for the data junkies.

 

[blueraja]

Thanks nova, but it looks like that link leads to another thread, and the pictures don't load (at least for me).

But, I get the general understanding of what they're saying. I just thought I read somewhere that 1st gear and reverse were split 50/50, but I understand that they're saying that its still variable based on engine speed and things like that.


Sent from AutoGuide.com App

 

[CNY_Dave]

Is that why I feel a slight rumbling sensation when I first start rolling from a light? Kind of like knobby tire sensation? It's just for a second on initial take off.

Could be, prolly when it takes up the slack in the rear drivetrain.