Wiring a switch for true 50/50 rather than 90/10

[Pathfinder]

I have a 2007 legacy 2.5i sedan with the automatic trans. Winter is coming up soon. Not only do I LOVE driving in the snow but I also have to drive up/down a mountain 5 days a week to get to my office. The business I work in doesn't have the luxury of snow days. There is a small bit of lag between when the car looses traction, and it goes into AWD. I have heard ways to bypass that but I'm not sure what the best method to do that is on my particular model. Ultimately I'd like to wire up a button or a switch to engage 50/50 split on demand. Is this do-able for my car, and is it safe?

Edited October 17, 2013 by Pathfinder

[matt167]

I think you could install a diode in the wire for the duty C solenoid so it does not backfeed the ECU. Then, run the full listed voltage for the solenoid to a switch to lock up the clutches. Should be full AWD at that time. Don't try to take tight corners because it will not happen..

 

Oh wait, I think you just subtract the voltage to keep it engaged . The FWD fuse applies full field to the solenoid to open it up

Edited October 18, 2013 by matt167

[subnz]

The easy solution is to get one with a manual transmission ie has mechanical 50/50 torque split  (80/20 to 20/80  with wheel slip)    so the drive is always there / no delay with  electronics deciding what to do    ( no electronics unless VDC etc ) also better engine braking on descent.

I have a 01 2.5 MT D/R OBW and l don't think/can't remember if  its ever lost traction driving on snow up ski field roads however  have had 2 or 3 moments down in the valley over the years on non snow icy curves (black ice on tarmac)  where the front has lost contact (nothing major)  with the road before putting winter tyres on (on spare rims )

Have seen  a few auto awd subarus  particulary legacies with spinning front wheels on numerous ocassions guess its the 90/10 setup.

Edited October 18, 2013 by subnz

[KiwiGL]

There is a way to do the electronic split, I have no idea how it's done but the first reply sounds like it would work. I'm sure someone else can confirm, it's been done on a few vehicles.

[presslab]

I know the older automatics applied a more aggressive AWD map when the shifter was moved into "1".  Yours being sportshift (right?), I'm not sure, but it's possible.

 

I believe the solenoid on > '06 models had reversed action from the earlier ones.  This would mean that to engage the rear driveline you would need to apply 12V to the solenoid.  A DPDT switch could be rigged up to switch between modes.  In one position the switch would connect the solenoid to the computer (normal) and in the other position the solenoid would be connected to 12V and the computer would be connected to a dummy resistor to ground.  The resistor would keep the TCU from throwing a code.

[Gloyale]

Definately the older ones you would CUT all voltage to the solenoid to give full pressure to the AWD clutch.

 

Not sure if the newer ones are reverse as Presslab stated above.

 

Either way that's the track you need to be on....a switch on the Transfer solenoid.

[idosubaru]

on older models you simply cut the one power wire to the Duty C solenoid - very simple.  install a switch for that one wire.  it is an excellent idea, i'm a huge fan and have done it multiple times.

 

i've heard the same thing - in H6 transmissions the transfer solenoid changes around 03 or 04 to a different operating scope.  I think CNY Dave is familiar with it...but not sure if 4 cylinder and 6 change in the same way/same time.  but yeah - you'd give it 12 volts all the time if it is indeed reversed in that way.  i haven't heard of anyone doing it on a newer transmission yet.

 

 mechanical 50/50 torque split 

it's not a mechanical 50/50 center diff - it's a viscous center diff so it's an open differential until slip happens, heats up the fluid, and then locks it.  Subaru made a 50/50 center diff in FT4WD transmissions with center diff lock in the late 80's/early 90's EA and ER vehicles which I prefer myself.  it has been said the VLSD center lock up is fairly fast, i'd like to see some videos or something on that. 

Edited October 18, 2013 by grossgary

[CNY_Dave]

If it has the multi-plate clutch and not VTD, you should be able to supply +12V to the transfer duty solenoid to get it to lock up fully.

Earlier models sent +12V to fully release the AWD, later models send 0V to fully release it.

 

The diode trick might work, or you might need to use a multi-pole switch to switch the TCU wire over to a resistor.

 

But, I thought at some point all the autos got VTD (the center planetary differential)?

[subnz]

 

grossgary, on 18 Oct 2013 - 12:33, said:
on older models you simply cut the one power wire to the Duty C solenoid - very simple. install a switch for that one wire. it is an excellent idea, i'm a huge fan and have done it multiple times.

i've heard the same thing - in H6 transmissions the transfer solenoid changes around 03 or 04 to a different operating scope. I think CNY Dave is familiar with it...but not sure if 4 cylinder and 6 change in the same way/same time. but yeah - you'd give it 12 volts all the time if it is indeed reversed in that way. i haven't heard of anyone doing it on a newer transmission yet.

it's not a mechanical 50/50 center diff - it's a viscous center diff so it's an open differential until slip happens, heats up the fluid, and then locks it. Subaru made a 50/50 center diff in FT4WD transmissions with center diff lock in the late 80's/early 90's EA and ER vehicles which I prefer myself. it has been said the VLSD center lock up is fairly fast, i'd like to see some videos or something on that.

 

Yes it is! Manuals have a mechanical viscous centre diff which distrbutes torque 50/50 normally until wheel slippage occurs when the( central diff similar to an LSD) viscous coupling heats up fluid with wheel slippage like you said and directs torque up to 80/20 or 20/80 in which direction its needed. It isn't able to / doesn't completely lock up like the 86/88 RXII AWD Leones (Ea82T) did with an actual central diff lock. (electric/switch)
The std manual doesn't rely on sensors/electronics/ecu to direct torque front / rear , except for manuals with VDC stability control.

Std Autos have a multiplate transfer clutch (electonics/sensors/ecu) instead of a central diff LSD (viscous coupling) in manuals.
and later Autos ie with VDC have both (planetary central diff (VTD) and multiplate transfer clutch)


http://www.awdwiki.com/en/subaru/

Edited October 19, 2013 by subnz

[nipper]

The easy solution is to get one with a manual transmission ie has mechanical 50/50 torque split  (80/20 to 20/80  with wheel slip)    so the drive is always there / no delay with  electronics deciding what to do    ( no electronics unless VDC etc ) also better engine braking on descent.

I have a 01 2.5 MT D/R OBW and l don't think/can't remember if  its ever lost traction driving on snow up ski field roads however  have had 2 or 3 moments down in the valley over the years on non snow icy curves (black ice on tarmac)  where the front has lost contact (nothing major)  with the road before putting winter tyres on (on spare rims )

Have seen  a few auto awd subarus  particulary legacies with spinning front wheels on numerous ocassions guess its the 90/10 setup.

Mechanical ones have a delay too. The viscous coupling has to warm up to thicken to cause the torque split.

[nipper]

When was the last time you changed the transmission fluid, that can work wonders on these transmissions, getting rid of any delays in action.

[NorthWet]

The manual in my 90 Legacy wouldn't allow the car to move at all without the rear driveshaft connected...

 

And just to throw gas on the fire, an open differential by definition provides a 50/50 torque split.

 

Cheers!

[idosubaru]

Yes it is! Manuals have a mechanical viscous centre diff which distrbutes torque 50/50 normally until wheel slippage occurs when the( central diff similar to an LSD) viscous coupling heats up fluid with wheel slippage like you said and directs torque up to 80/20 or 20/80 in which direction its needed. It isn't able to / doesn't completely lock up like the 86/88 RXII AWD Leones (Ea82T) did with an actual central diff lock. (electric/switch)

you repeated everything i said.  technical hair splitting aside:

1.  a VLSD locks up when the fluid heats up - or *it slips*

2.  an auto transmission locks up when sensors tell it - or *it slips*

 

technicalities and theory discussion add nothing to those two symptoms.  they both require slippage to operate. there may be room to discuss which is quicker or Northwet's comment, but they both *require* slippage - or a delay...exactly what the original poster doesn't want. this guy doesn't have an MT anyway and the AT is better since you *can* control "lock up" yourself - with no slippage required.

 

I want to control when it locks - not have VLSD fluid or electronics do it for me...same as the original poster of this thread.

can't do that with a MT, you can with an AT.

[subnz]

you repeated everything i said.  technical hair splitting aside:

1.  a VLSD locks up when the fluid heats up - or *it slips*

2.  an auto transmission locks up when sensors tell it - or *it slips*

 

technicalities and theory discussion add nothing to those two symptoms.  they both require slippage to operate. there may be room to discuss which is quicker or Northwet's comment, but they both *require* slippage - or a delay...exactly what the original poster doesn't want. this guy doesn't have an MT anyway and the AT is better since you *can* control "lock up" yourself - with no slippage required.

 

I want to control when it locks - not have VLSD fluid or electronics do it for me...same as the original poster of this thread.

can't do that with a MT, you can with an AT.

 Apologies I shouldn't have got involved in this discusion . because   I don't like automatics.

The question  I   have is that  why was I able to drive away ( 01 2.5 OBW MT D/R -no  VDC) without spinning my wheels, when the auto legacy (2nd gen mid 90's)  wagon parked beside me spun its front wheels for 3 seconds before it moved away before me. This was on a mild slope on packed snow in  a skifield car park.(This was a chains on day for 2wds)

Edited October 21, 2013 by subnz

[forester2002s]

The difference could be the tires...

 

A car with all-seasons (hard rubber tread), and somewhat worn down, might spin its wheels.

 

However a car with good winter tires (soft rubber tread) might drive away easily.

[CNY_Dave]

My wifes forester ('04 4eat) and my outback ('03 4eat) both have no noticeable delay for the AWD to 'kick in', some cars seem to have a slight delay as a normal fact-of-life, but something there has to be different...

[idosubaru]

 Apologies I shouldn't have got involved in this discusion . because   I don't like automatics.

The question  I   have is that  why was I able to drive away ( 01 2.5 OBW MT D/R -no  VDC) without spinning my wheels, when the auto legacy (2nd gen mid 90's)  wagon parked beside me spun its front wheels for 3 seconds before it moved away before me. This was on a mild slope on packed snow in  a skifield car park.(This was a chains on day for 2wds)

no apologies needed, talking on forums isn't as easy as in person. 

 

doubtful both had the exact same brand, tread depth, and age tires.  a FWD with Nokian snow tires could outperform a 4WD with all seasons in certain situations.  then there's ground clearance, weight, different parking spots aren't exactly the same...one could be rutted, icy, the other packed snow, more slope, more uneven...etc. maybe that car wasn't in great mechanical condition - high miles, warn clutch packes, there are rear VLSD's...but they can not work well sometimes...i've seen Subaru's get out when another 4WD vehicle coudln't and those are the stories shared on subaru forums...but i've seen the other way around happen too - a Subaru get stuck when it seemingly shouldn't. and there's probably 10 other variables i haven't thought of.

[subnz]

no apologies needed, talking on forums isn't as easy as in person. 

 

doubtful both had the exact same brand, tread depth, and age tires.  a FWD with Nokian snow tires could outperform a 4WD with all seasons in certain situations.  then there's ground clearance, weight, different parking spots aren't exactly the same...one could be rutted, icy, the other packed snow, more slope, more uneven...etc. maybe that car wasn't in great mechanical condition - high miles, warn clutch packes, there are rear VLSD's...but they can not work well sometimes...i've seen Subaru's get out when another 4WD vehicle coudln't and those are the stories shared on subaru forums...but i've seen the other way around happen too - a Subaru get stuck when it seemingly shouldn't. and there's probably 10 other variables i haven't thought of.

 Thanks fair comment,  a little off topic now:

Talking of rear LSD's,   my sister and brother in law who are farmers had a 2000 Toyota Hilux doublecab 3.0 N/A diesel part time 4WD with rear LSD, it spent most of its life off road on farm in muddy conditions but used like a car on road too. It was amazing how

further it could go in 2wd before having to select 4wd in the mud compared to their previous Hilux 4WD with no rear LSD.

[idosubaru]

yeah man, LSD increases traction 50% from 2 to 3 wheels.

[ivans imports]

My first step to slugish awd is a drive with 2wd fuse in this holds soilniond open and will clear any debrie that may be pluging curcit about 5-10 kms with 2wd fuse in then try awd out

[CNY_Dave]

My first step to slugish awd is a drive with 2wd fuse in this holds soilniond open and will clear any debrie that may be pluging curcit about 5-10 kms with 2wd fuse in then try awd out

 

Sticking the fuse in and removing it a few times with the engine running, car in 1 and someone inside with the brake on ( ) might help too, the pressure pulses might help knock any crud loose.

[presslab]

The 4EAT MPT (and by extension VTD) do not require slippage to transfer torque.  The torque transfer is calculated based on throttle position, gear selector position, current gear, and road speed.  If the torque transfer from the calculation is not enough and the wheels still slip, then the computer will detect this and apply even more torque.  If there is a mechanical problem with the MPT (which is common) then the calculated torque transfer will not be adequate, and there will be a delay in torque transfer.

 

The viscous coupler of the manual transaxle does not require slippage either, as it is paired with a differential gear set.  In this way the torque is 50/50 if all wheels have traction.  When one wheel loses traction, the viscous coupler will increase torque transfer to the front or rear, whichever has more traction.

 

Neither require slippage to transfer torque.  In my opinion both systems are excellent, when working properly.

[ivans imports]

On race buggy I ran a line direct to awd clutch pack gave it full line preshure no slipen there 100% locked as soon as its running 8 years in no problems with awd setup

[CNY_Dave]

Would just setting the solenoid the right way (0V or +12V) be different than a more custom method?

 

As I recall the fluid schematic fill line pressure goes to the spool valve controlled by the solenoid? Or does it get a regulated feed?