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2007 Forester XT
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Thank you to everyone who has contributed to this discussion! I have been working on this mod, and finally got it installed and working on the weekend in a 2007 Forester XT. I have some feedback to add, but I cannot post images because I'm new! As soon as I can add images, I will.
 

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Registered
2007 Forester XT
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15 Posts
Thank you to everyone who has contributed to this discussion! I have been working on this mod, and finally got it installed and working on the weekend in a 2007 Forester XT. I have some feedback to add:

**My apologies in advance for the very long post**

The aim of this switch is to force the Transfer Duty Solenoid to lock the drive 50:50 front and rear. This maximises the drive to all wheels thus reducing the chance of getting stuck.

For a Turbo Forester, the aim of this device is to provide current to the Solenoid and resistance to the TCM when the switch is ON.
For a non-Turbo Forester, the aim is to provide NO current to the solenoid and resistance to the TCM when the switch is ON.
For both models, the aim when the switch is OFF is to connect the existing wiring (Solenoid->TCM) so the TCM can manage the behaviour of the Solenoid.

I found that this later model SG was different to what had been documented in this thread.
I’ve been working on a 2007 Subaru Forester XT and have documented what I’ve done below.


The TCM is located up under driver’s side dash toward the centre console – a black box with 2 white plugs – labelled WE SUBARU 31711AL110 112300-9170 Denso.
1. I unbolted it from frame using 12mm socket.



2. Find the correct wire.
a. The wire I required is circled above – on the right-hand plug when the writing is upright. The lower plug when the TCM is bolted to the vehicle frame.
It’s plug B54 wire 5 that we need – white with green stripe (WG)
This colouring is similar to other models, but its location in the plug is different. See the snippet from the Service Manual below.





3. I back-probed the connection and monitored the voltage change while shifting between gears and accelerating hard (to generate wheel-spin and force the TCM to shift power to the rear wheels)
This confirmed I had found the correct wire:
- Voltage <1 when in park
- Voltage approx. 1.7 when in Drive 0% throttle
- Voltage approx. 3.8 when in 1st 100% throttle

4. To build the switching mechanism, I used:
- 1 x LY2NJ Relay – Double Pull Double Throw 2 Normally Open, 2 Normally Closed - https://ebay.us/hfBLsy
- Traction Rocker switch - https://ebay.us/gwfSRw (can use any switch you want)
- 2 x 8ohm resistors in parallel to give 4ohm in total: https://ebay.us/yS0paE
- Heatsink - https://ebay.us/446jBY
- A couple of metres of twin core wire
- A bit of heat shrink tubing to keep stuff neat and tidy
- A number of spade and ring crimp connectors
- A couple of bolts to connect the resistors to the heatsink

The smarts of all of this are in the Relay. Note that we require a Double Pull Double Throw, because we want two actions to occur when the relay is ON (current to Solenoid, resistance to TCM). Note that the relay essentially works as two parts – the left Common (COM) is only connected to the left Normally Closed (NC) or the left Normally Open (NO). Never to the right side.
The first thing is that the COM terminals are connected to the Solenoid (Left COM) and the TCM (Right COM). **I actually did this as the very last thing, and built the rest of the kit on the bench first, but it makes more sense to think about it happening first**
When there is no current supplied, the NC terminals are connected to the COM terminals. By looping a wire from one NC to the other, when no current is supplied the circuit is completed. This essentially is the same as not having cut the wire at all.



Next step is to provide power to activate the relay.



When current is applied to the COIL terminal, the relay disconnects the NC terminals from COM and connects the NO terminals to the COM terminals.
I wanted 12v to be applied to the Solenoid when the switch is ON. So I looped 12v from the switch wire to the NO terminal on the Solenoid side.



Once this is done, when power comes in from the switch, the Solenoid is disconnected from the NC loop back to the TCM, and connected to 12v from the left NO terminal. Great! We get 12v to the solenoid.

Next step is to provide resistance to the TCM.



I did this by putting 2 x 8ohm resistors in parallel to give a total resistance of 4ohms. I wired the other side of these to ground, using the existing ground connection I had on the relay. These resistors are turning current from the TCM into heat, so I mounted them on a heatsink. I also bought 50w resistors, which should be overkill but they are larger which will also help with heat dissipation.

5. Once I had the device built and tested, and I’d found the wire and triple-checked it was the correct one, it was time to install. I cut the wire and put a male and female spade terminal on each end, so that if I wanted to take the device out, I could without any issues. I then connected these terminals to ones on the device.
6. Next was finding a power source. I ended up tapping in to the cigarette lighter circuit and earthing to a bolt in the centre console. I used a t-tap to get positive and a ring terminal for ground.
7. Next was finding a place for the switch – I went with centre console. The blanking plate popped out easily and I fed the wires (both the positive/ground pair from the cigarette circuit and the positive/ground pair going to the relay. I connected these to the switch, on which I had already jumpered the ground pins. I’ll show you what I mean below. This is only to keep the wiring neat.




8. Once this was done, we were finished! I tucked the relay and resistors in the side panel of the centre console just below where the cigarette wiring is. I put all the panels back in place and re-tested. Everything worked as expected.



9. The best test for this is driving in a tight circle on pavement with your feet off the pedals. With the switch OFF, the car should happily go round in a circle (power distributed front/rear as required). With the switch ON, the car should come to a stop in around 90 degrees or less. Ours was almost instant. This is because the front wheels follow a shorter path (inside line) and this generates torque bind as the centre diff no longer allows that power to be shared – it’s locked 50:50

10. Obviously, all the normal caveats apply. Do this at your own risk, I’m telling you what I did in the hope it will help someone to do a good job. I’m not telling you what you should do. You get to make your own stupid decisions! Also, this function is best used when you know there is a difficult obstacle ahead – turn it on before you get to the obstacle and turn it off once you’re clear. Not to be used on pavement. Not to be used for extended periods of time.

11. The only thing I wasn’t sure of is the voltage – the manual says 2-3v, we saw up to 3.8v, and we’re supplying 12v to it. I don’t expect this would be a problem, but I’d appreciate anyone’s advice or experience on that?
 

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Registered
2002 Forester 4EAT w/ Center Diff Lock
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8 Posts
Like the toggle switch. Did you steal it from an old F-15?
Haha, nah. It's just a switch cover I bought off amazon. Since I don't have an indicator light for when it's on, I didn't want to accidentally hit it and leave it on when it shouldn't be.
 

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2007 Forester XT
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15 Posts
You're absolutely welcome. I'd learnt so much from the rest of this post, (and there is so much info in it) I thought I should collate everything I'd learnt and put it into a single (hopefully coherent) post.
 

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2010 XT Premium Auto 4 Speed Auto
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5 Posts
Hi, my name is William and this is my first post on this forum having just found it.

I have read most of this thread but am still not sure if my 2010 Forester XT Premium 4 speed auto can be modified to be able to alter the front/rear torque split.

I have a number of power and handling mods on my Forester and I am very happy with the exceptional 0-100k performance which is in the very low 5s and handling is quite good considering the height of the vehicle.
My one real complaint is that it performs too much like a front drive especially when entering from a side street under power, I have to be careful not to spin the front wheel(s).

I want to be able to direct more power to the rear wheels to avoid this, can it be done electronically?

I read earlier that manually selecting gear 1 will deliver a 50/50 split is this true?

I will be trying this afternoon but am keen to hear what you guys have to say.
 

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12,715 Posts
G'day & Welcome @Bigwbb

Manually selecting 1st or 2nd on a 4EAT along with 75% throttle will direct more power to the rear wheels (the actual split has been often debated so I won't go there).

Are you sure that you are getting some power to the rear wheels under normal conditions? Does your model have a "FWD" fuse slot and is it empty?
 

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2010 XT Premium Auto 4 Speed Auto
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5 Posts
Torque split and FWD fuse response to Kevin

Hi Kevin, thank you for your response.

I couldn't find a FWD fuse slot anywhere and there is no 'FWD' display on the dash.

In a straight line with full throttle I have to wrestle with the steering wheel a little to keep it in a straight line, that is fine and frankly a bit of fun and the front wheels will spin only a small amount as it launches, so I am sure that power is getting to the back wheels.

The real problem is when entering traffic from a side street under power where the front wheel with least grip starts to spin and the traction control starts carrying on like a pork chop - turning off VDC helps but there is still a fair amount of wheel spin.
This is in no doubt due to the fact that the car's weight is transferred to the rear thereby lifting the front end, especially the left front wheel when turning left and of course the right front wheel when turning right.

The ultimate would be to get 40/60 or even 20/80 torque split (F/R) via a switch somewhere but I don't know if this is even possible.

I drove a mate's 2016 Audi SQ5 twin turbo diesel, the power (0-100kph) is comparable but the Audi keeps pulling much harder after that but I am not concerned with speed beyond around 100kph anyway, just getting to 100kph quickly.
The most important difference was the obvious differences in torque split, no front wheel spin problems with the Audi.
 

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2007 Forester XT
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15 Posts
@Bigwbb Your 2010 would be the first of the SH models, right?

I'm not familiar with the SH, but if you have a Service Manual you'd be able to work out if it has a Multi-Plate Transfer (MPT) Clutch with a Transfer Duty Solenoid, or Variable Torque Distribution or one of the other AWD systems.

Have a look at these to get an idea about how your AWD system works:
https://www.stanleysubaru.com/blog/2012/march/22/how-does-subaru-symmetrical-all-wheel-drive-work.htm
Subaru AWD System Fully Explained | YouWheel - Your Car Expert

If it did have MPT (and probably VTD too), i think it would be possible to put in a variable voltage regulator in along with the switch and use this knob to control the percentage of drive to the front/rear. You'd want a voltage meter to show you want the current voltage was too. And use the switch to turn it off altogether.

For example, turn the knob down to zero to get front wheel drive. Turn it up to 12 to get 50:50 front-rear.

The problem is you'll need to know BEFORE you need the additional traction, and you'll need time to turn it on and adjust the knob to the right value. All BEFORE you need it. What you probably want is the TCM to do this for you, but more aggressively than it currently does. That's a much more difficult problem, and one you wont fix with a switch and a knob.

The switch I've put in was done with off-road performance in mind. You can see the obstacle before you get to it, you can flick the switch and get a better split of power. You can turn it off once you're clear of the obstacle. It doesn't play nicely with turning on hard surfaces, which is exactly what you're trying to do when flying out of a side street.
 

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2010 XT Premium Auto 4 Speed Auto
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Torque split... again, still

Hi Alexdv, thanks for your help.

I spoke to a trans specialist here in Adelaide who is widely accepted as 'the man' in SA and I can personally vouch for this as he has built a rock-solid trans for me in the past for a 11.8 second quarter mile Holden Commodore.

Yes apparently it is a MPT Clutch system with a Transfer Duty Solenoid, the problem is that the way the solenoid works is different in the Forester than any other Subaru.
Without going into details the 50/50 split could be achieved quite simply but it would put too much load on the solenoid when engaged and therefore could only be used for moments at a time which makes it a bit of a pain (if left on for too long it would quickly burn out the solenoid).
Ideally I would like to be able to engage it and leave it on for as long as necessary rather than having to be ever-vigilant in turning off right after the need is taken care of - bit of a pain.
The only other way is to alter the software that controls the solenoid which is obviously not cost-effective even if you could find someone to do it.

And just for the record, I never 'fly' out of a side street, I simply want to apply power confidently thereby not holding up others on the road by entering busy traffic and then going slow.

Again, thanks for taking the time to respond, I hope this post helps others with this Torque split business.
 

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2007 Forester XT
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Thanks for the follow-up Bigwbb.

Yep, I think you're right on the money there - the solenoid solution isn't going to work for what you need to achieve.
It would be great if it was possible to start with a split closer to 50:50 (rather than a front-wheel bias as is standard) and allow the TCM to adjust as needed.
But this sounds much more like a TCM software adjustment than the sort of changes people have made in this thread!

I certainly wasn't trying to suggest you weren't driving safely! :)
 

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2010 XT Premium Auto 4 Speed Auto
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5 Posts
No worries

Hello again Alexdv.

I think you are right, I will contact MRT in Sydney to see if anyone has actually looked at modifying the TCM software in order to achieve a 50/50 split as the norm as you suggest.

Mate, no worries - I just didn't want anyone to get the wrong idea - all good.

If I have any success with the MRT team I will let you know.

Cheers.
 

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2008 Forester SH 2.0 XT Automatic
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4 Posts
@alexdv @Bigwbb Confirmed!!! On the first model of the SH forester ,the switch works. The wire is at connector B55 pin 5 , YG just as shown in the manual. Giving the Solenoid 12v enables the lock up at 50/50 to happen and to experience the torque bind in a tight circle.

As mentioned earlier its best to use it minimally on obstacles and then OFF it.
Pet peeve with the SH forester is no switch provisions given.
Not sure how it will interact with the VDC when it kicks in and the switch is on. But best guess is the VDC will compliment the mod when it kicks in. i will test it over time to truly find out.

This thread has been great with detailed info . Thank you to all you pioneers.
 

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2010 XT Premium Auto 4 Speed Auto
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Hi ragerice,

Thanks for the info, I am keen to find out how the manual switch that you mention and the VDC interact.

I spoke with a guy called Quinton at MRT in Sydney regarding this FWD bias business.

Many people in this thread will probably be aware of MRT, they provide a number of upgrades for Subaru and Mitsubishi ecus along with associated mechanicals.

Quentin has informed me that power is distributed at 25% per wheel as standard and that the TCM then attempts to alter those figures based on load, wheel slip etc etc.
This seems to fly in the face of reality when behind the wheel, I suspect that he is probably right but that the TCM is simply not quick enough to adjust, especially when it is trying to keep up with more power than originally anticipated, not sure.

Either way modifying the TCM software is not an option as MRT do not have access to it - unlike the engine ecu software which they modify extensively.

Not sure if there are any other players in the market regarding TCM software.
 

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2007 Forester XT
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15 Posts
Great work @ragerice!

Glad to hear it works on the SH too. Thanks for confirming the wiring required too.

If yours a turbo or NA? Seems to make a difference to wiring too.

On my hitlist at the moment is swaybar disconnects! And the torq masters r160 auto locker once it's released.
 

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2008 Forester SH 2.0 XT Automatic
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4 Posts
@Bigwbb VDC still kicks in with the manual switch on but since the TCM cannot access the transfer solenoid the lock up still remains 50/50 but am guessing the Stability control will still do its thing on other fronts like the braking of individual tyres and cutting engine power if need be according to the parameters its fed.

My best hope is that with stability control on and lock up at 50/50 it might act like a virtual lsd. And just to note i also installed the complete VDC off switch via the yaw box . This allows for stability control to be off while still maintaining abs and cruise control unlike pulling the fuse off which disables all. This gives you complete control of the car avoiding those times when VDC takes away engine power from you.

Yeah i know MRT , and i think the solution you are looking for might be tricky because this mod i believe should be used sparingly on tarmac as it would cause quite a bit of wear and tear and not good for cornering at all. And the cars have different torque split to a max of 50/50 from 0 to 12 v being received on the transfer solenoid. So for rear bias am guessing unless the solenoid is engineered differently it will be impossible.

on Modifying the TCM with the research ive done, no one seems to have cracked it...?

Il post progress as i experience it more.
 

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2008 Forester SH 2.0 XT Automatic
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4 Posts
@alexdv Thank you .
Your work gave me the confidence to go through with it.
Mines a turbo sh 2.0 first model.
For the SH the disconnects its abit tricky but really not gone in for that deep dive but will do.
The locker , am just weary on the day to day driving as a daily . Once that is cleared il get direction from there.
But have a feeling i will still do it either way lol
 
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