The problem with the auto box is that it’s permanent front wheel drive with an electronically activated clutch pack setup that sends power and torque to the rear wheels. This is why the lock up switch is such an effective mod.
As for the locker, as others have said, it’s locked all the time. Once one wheel rotates faster than the other via the larger outside ark of cornering, it is unlocked and allowed to freewheel.
Or your driving technique in a vehicle with independent suspension all round.
Cheers
Bennie
That's the system that most AWDs are using but the electronic part of Subaru's AWD, as well as Audi's, is controlled via the
Transfer Control Duty solenoid which only adjusts the torque distribution to the rear.
Without such solenoid, there is proper torque bind or there is always torque to the rear, proving that all Subarus, and Audis, are AWD all the time (active AWD). It's actually a fool-proof system that gives owners torque bind or more torque to the rear when the solenoid wears out. So the electronic part is the control, not the activation. The ones that are electronically controlled are the ones that are reactive systems from Toyota, Honda, Kia, etc.
We already know that Subarus are AWD all the time but since the TCU codes are closed-source, we can only use whatever we can measure. That's where FreeSSM or any SSM comes in. According to
FreeSSM,
1A on the solenoid = 100% torque transfer to the rear, which rarely happens.
0.16A is approximately 42% transfer to the rear. One must think that when the solenoid is out, it would give 0A and no transfer to the rear but that is where the mechanical fail-safe of the design comes in.
The solenoid just completes the AWD circuit and without it, there is nothing limiting the torque transfer to the rear, hence the torque bind. FreeSSM proves also that the system is not only active but extremely dynamic.
These data have already been discussed and documented extensively in subaruoutback.org. There results below from
ntippet can be replicated by Subaru dealerships when you ask them to do it for you:
Discussion Starter • #38 • Oct 22, 2011 (Edited)
Alright I have a whole new set of measurements ready.
I will need to classify these into categories from now on.
The TCU Stratgey Has Very Dynamic AWD Control
But we already knew this right?
Transfer Solenoid % engagement is directly affected by:
-Wheel Speed
-Gear Selection
-Throttle Position
These are the first set of measurements I took for the Transfer Solenoid.
From now on I will be referring to them as:
Static Control
This is what the TCU outputs when the vehicle is stationary with no throttle input.
Gear | Duty Cycle | Amperage
P - | 5% | .01A
R - | 42% | .16A
N - | 5% | .01A
D - | 42% | .16A
3 - | 42% | .16A
2 - | 42% | .16A
1 - | 55% | .27A
I then stated the following:
- Full lock up is achieved in 2 ways:
- 1: 100% Throttle Engagement
- 2: TCU detects front wheel slippage from the wheel speed sensors (speed differential between the front and rear wheels)
- This delivers a maximum of 95% duty cycle and 0.95 A to the solenoid.
Clarification
1: Vehicle stationary, in gear, 100% throttle - This can also be called a stall test, requires high brake input to hold the vehicle stationary.
2: This test I will have to confirm once the snow files, I know it will increase %, but by how much is the question...
Now we move into the next category of measurements.
From now on I will be referring to them as:
Dynamic Control
I have only taken the % duty cycle, posting the V & I is redundant.
This is how the transfer solenoid is controlled in the real world, driving down the road.
4th-TCC Engaged
WOT - 43%
Cruise - 38% @ 60 MPH
Decel - 41%
4th-TCC Off
Did not get these measurements, would have had to eliminate the TCC temporarily to get this.
3rd
WOT - 52%
Cruise - 38% @ 50 MPH
Decel - 42%
2nd
WOT - 60%
Cruise - 42% @ 30 MPH
Decel - 43%
1st
WOT - 95% - drops off to 80% & lower as speed increases beyond 1-2MPH
Cruise - 44% @ 10 MPH
Decel -
The highest I could get the duty cycle to jump was in 1st gear full throttle @ about 1-2 MPH.
From here the faster the car travels the more the duty cycle drops off.
Once any speed is measure through the wheel speed sensors values drop off 5-10% or more.
Another interesting note:
If a change in the Correction of Transfer Duty Ratio has been set in FreeSSM it will make the change across the board under all conditions.
The key:
Every 1% change in FreeSSM results in an equivalent 1% change of duty cycle for this solenoid.
The FWD impression is when the centre diff wears out due to donuts, uneven tire wear, etc. Where the wet clutch isn't as effective in holding torque anymore. That's the extreme, though, as the Transfer Control Duty solenoid fails first and when binding is felt on high traction surfaces, the owner should replace the the solenoid immediately to save the centre MPT diff. The same feeling is felt when the viscous centre diff of manual transmission wears out completely. Cheers.
EDIT: I formatted the results differently so they are easier to see.
EDIT 2: My brother experienced the solenoid failure first hand on his BP5's 4EAT so he initially went to a non-Subaru workshop and the mechanics all said, "What happened? It's like the centre diff is locked fully like some 4x4s!" They had to call in a Subaru mechanic to diagnose the issue. The mechanic explained that with the solenoid failure, the mechanical system just isn't controlled and would send the same amount of torque to both axles all the time. I drove the car before that and felt like going off-road, haha.
EDIT 3: FreeSSM can adjust the average amperage for each gear. I have discussed this with some Subaru mechanics and they said that raising the first gear average from 55% to 60%, which they can do, then using the diff lock mod, which they won't do, will significantly increase the TorqueMasters locker performance significantly. Some PNW mechanics are already doing the mod, they said.
