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4EAT Diff Lock Switch


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24 replies to this topic

#1 eulogious

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Posted 28 October 2009 - 01:15 PM

Hello all, so I was reading around the internets today and I stumbled across this:

http://www.rs25.com/...da-lite-12.html

Once I found this out, I want to know more so I jumped over here and found these threads talking about it:

http://www.ultimates...ht=4eat locking

http://www.ultimates...t=duty solenoid

http://www.ultimates...ead.php?t=50264

To sum up all the previous posts... In order to achive "true" AWD (meaning no delay/tire slip before AWD is active) you can disable the duty C solenoid (which is in charge of the MPT clutch on the 4EAT) and essential lock the MPT clutch to a 50/50 split ratio. Now when you just put a switch in to disable the duty C solenoid, the TCU will throw a fit and cause the AT Temp light to blink something like 16 times. In order to prevent the TCU from throwing out codes you can build a resistor block to fool the TCU into thinking that the solenoid is still there by providing the same resistance the solenoid provides so you don't get the blinking light and the TCU throwing out codes.

Here's a diagram on the whole setup thanks to obsolete over at the rs25 forums for the diagram. It can also be found on page 5 in the first link. I take no credit for this:

Attached File  resistorblock.gif   8.24K   63 downloads

The biggest downside to this is you might blow your 4EAT up because you are causing too much hydraulic pressure to build up when you disconnect duty C solenoid because the internal spool valve is also controlled by the duty C solenoid and when internal spool valve closes it cause pressure in the clutchplates to build up and blow up the tranny. I am summarizing very quickly here, but that is the jist of the all the threads.

So with all that in mind this is what I am thinking. I want to do all of this, but add another circuit in that would give a set amount of voltage to the duty C solenoid, say like 55% duty cycle (~55/45 split). This way the solenoid is not closed all the way, allowing the internal spool valve to remain partly open and not allowing pressure to build, solving most of the issues, but giving you instant 55/45 split allowing for better snow/mud/crap starts. I would just use a DPDT switch (or similar, not exactly sure what switch to use) and instead of connecting an LED up (maybe work on that later??) I would wire my new voltage limiting circuit to it instead. That way when I turn on the "diff lock" it would bypass the TCU, and activate my voltage limiting circuit at the same time :grin:

I don't want this to turn into a discussion on whether this is a good idea or not (the mod itself), I am going to try it, and if all else fails I am going to do the mod following the instructions in the first post and take the risk. I want this to be a discussion on whether or not this idea will work...

So I have 4 questions:

1. Am I on the right track here? The TCU sends a different voltage to the solenoid to control the split depending on conditions, so I should be able to do the same...

2. Does this idea solve the issues of building up pressure and the clutch plates failing?

3. Do I need a PWM controller circuit to reduce the voltage(PWM) to the duty C solenoid (much harder)? Or can I just use resistors to lower the voltage(non-PWM) to the duty C solenoid using the 12v from, say, the cigarette lighter (much easier)?

4. I am going to be doing this on my 1990 loyale turbo wagon w/4EAT, so does anybody know which wire goes from the TCU to the duty C soleniod on my car? I have the FSM, but it doesn't have anything for the 4EAT, and I can't find any wiring diagrams that I can read for my model (ae82), all I find is legacy and impreza stuff.

I am going to be consulting with a good friend of mine who is an EE, so he should be able to help me with all the heavy lifting (soldering, math, etc) to try to make this work. Also, if I do succeed I will post diagrams and pictures with part numbers and all that jazz. This mod is awesome, but having the added benefit of not completely locking the MPT clutch would make it perfect, but I only hope :)... More to come!

Edit: I should add that I am not an EE in any way, shape or form. There is probably some technical stuff missing in here, but the concept is what's important :)

Edited by eulogious, 28 October 2009 - 01:20 PM.


#2 grossgary

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Posted 28 October 2009 - 01:45 PM

this has all been talked about before including complicated cycle switches and variable controllers, etc. that's all discussed here. good job on some research an such, nice job, seems like you got a good grasp on it.

there's no damage to be done for nominal driving situations. it's not going to hurt anything if you don't abuse it - like forget it's on, etc.

any amount of work you put into varying the duty cycle is over kill - so essentially do whatever you want - whatever puts your mind at ease or makes you feel good. once you get to that level, you're golden. or if you really do need it, it's going to depend on your usage i guess if you're really tearing it up with your car.

for general daily driver useages, including rough, mountain, unmaintained roads i drive on a basic switch is all that is needed.

#3 eulogious

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Posted 28 October 2009 - 01:56 PM

for general daily driver useages, including rough, mountain, unmaintained roads i drive on a basic switch is all that is needed.


Exactly my thinking. That's why I am going to do it, even if I can't get the voltage limiting circuit working. I was just going to put a switch in, and then I found the other thread, which starting spawning ideas from there and here I am...

I just don't like to have loose ends (the TCU throwing out codes) if I can prevent it, especially if someone has done all the work for me, all I have to do is follow directions :) I am also the type to try to experiment and like to mod things, so this makes for a good project. I would totally not be even going down the road of messing with anything that might involve a PWM circuit, but a really good friend of mine gets off on that stuff, so I figured it would give us both a sweet project to try. That's really the only reason I am doing it. Peace of mind is more of a side benefit in this case ;)

this has all been talked about before including complicated cycle switches and variable controllers, etc. that's all discussed here. good job on some research an such, nice job, seems like you got a good grasp on it.


Thanks, I love the search button :)

Edited by eulogious, 28 October 2009 - 02:00 PM.


#4 eulogious

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Posted 29 October 2009 - 02:43 PM

Anyone?? I guess my main concern is my idea about the 60/40 split and is this going to solve the issue with the internal spool valve? I know nothing about automatic transmissions, so if anyone with knowledge about auto trannys could help me out with this, that would be sweet! I don't want to continue researching this if it won't have any improvement over just installing a switch.

I am making progress answering all my other questions, but if anyone else can help it would save me some time! Thanks!

#5 grossgary

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Posted 29 October 2009 - 03:34 PM

have you read the appropriate Factory Service Manual spec's and operational details from Subaru? I'd start there I suppose.

i didn't check all your links, did you find the other guy talking about building a programmer for this same purpose? that's the only thread i can ever think of that was mildly tech savy about this.

Anyone?? I guess my main concern is my idea about the 60/40 split and is this going to solve the issue with the internal spool valve?

no one on here has quantifiable information on this that i know of. i don't know of any auto trans designers on the board, i wouldn't give a rip what they have to say anyway personally! i work with half a billion dollar toys (NASA birds), these little Subaru's really don't bother me. trans blows up...put another one in there...but i haven't had any trans blow up yet.

Edited by grossgary, 29 October 2009 - 03:37 PM.


#6 Niku-Sama

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Posted 29 October 2009 - 09:40 PM

do you really need this though?
i notice this trans seems to do pretty well at deciding where power needs to go where, when. better than most

#7 zyewdall

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Posted 29 October 2009 - 11:02 PM

do you really need this though?
i notice this trans seems to do pretty well at deciding where power needs to go where, when. better than most


Yes, they're not bad stock... but some of the old posts from Andyjo when he first did this to his OBS seemed like it made quite a bit of different being in 4wd vs normal awd. I can't find those any more (I think they may have been in the off-road forum?).

#8 zyewdall

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Posted 29 October 2009 - 11:15 PM

http://www.ultimates...ead.php?t=49618

Found the thread talking about side by side tests with the locked center on the 4EAT. Sounds like it's worth it...

#9 eulogious

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Posted 30 October 2009 - 05:33 AM

no one on here has quantifiable information on this that i know of. i don't know of any auto trans designers on the board, i wouldn't give a rip what they have to say anyway personally! i work with half a billion dollar toys (NASA birds), these little Subaru's really don't bother me. trans blows up...put another one in there...but i haven't had any trans blow up yet.


That's cool, I was talking more about the logic involved, and if anybody who knew about auto's could verify that logic. I should have worded it differently, but it's a moot point now...

I have decided that I am not going to try to create a 60/40 split. After talking with defcon5 over at rs25, I decided that it's not really worth the bother. There's quite a bit more I would have to do in order for this to happen, and there would be very little benefit in doing so, so why bother. Besides that defcon5, several others over at rs25, and grossgary have not had any problems with this mod (as long as you use the mod correctly, which is what I will be doing).

Now I am at the point of trying to locate the wire for the duty C solenoid. In doing even more research, I found this thread over at subaruxt where grossgary did this mod to his xt6:

http://www.subaruxt....r diff&start=15

So this gave me inspiration because I think that I am close. Using the diagrams that I got for the 4EAT show that same connector in my car, but the pinout numbers are different. It's a different car, so ya, that makes sense, but all the wires colors were the same. Sweet I thought, I will just go look at my car... I found the plug, but all the wires are on the opposite side. The same colors, just flipped like this (it won't put in the spaces so the formating is messed up, but you get the idea):

Diagram:
2 1
6 5 4 3
10 9 8 7
12 11

Mine:
1 2
3 4 5 6
7 8 9 10
11 12

Does that make sense? The order and color of the wires are the same for my car, just on the other side. Here's the diagram that I am referring to. The red circles are what I think the Duty C Solenoid circuit is. The blue rectangle is the plug that I am referring to that is flipped on me.

Attached File  Duty C Solenoid.jpg   34.22K   25 downloads

I think the reason for this is because I have a turbo. Defcon mentioned that the legacy turbo wire color was different from the NA, so it would make sense that they would change the layout to make it different on the turbo, if you follow that same logic. I also noticed that there was no "green/red" wire coming off of the plug, at first. This confused me a little. After looking at the plug some more, I found the "green/red" wire going into the plug from the transmission, and the color of the wire coming out going to the inside/TCU was a "pastel" green/red wire. It's totally lighter and a different shade of green than the one coming off of the transmission. That was my AH HA!! moment. When I was looking for the green/red wire, I was looking for a DARK green and red wire, not a PASTEL one :| So I followed this wire as far as I could until it went inside the car. I then proceeded to look at my TCU and see if there was a pastel green/red wire on it. Sure enough there is :banana: But I don't want to get too excited, as I don't have my DMM on me, I can't test it to find out for sure until I get home and have the time. There is no dark green/red anywhere else but there are several other dark green wires, so I thought that the green/red one would be the same shade as the others.

grossgary, was this the wire that you ended up using (the one in the engine bay) for this mod?

I can almost smell success...

#10 john in KY

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Posted 30 October 2009 - 11:26 AM

The flipped flopped pinouts could be caused by you looking at either the male or female side of the plug and comparing the wrong end with the diagram if this makes any sense. If you compare the two connectors side by side you can see how one is the mirror image of the other .

/12345.../ and \...54321\

#11 Gloyale

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Posted 30 October 2009 - 12:10 PM

LEgacy Pinouts are totally different.

Don't guess here.

If you have the an 88, 89, or 90 electrical FSM(sec 6) you DO have the diagrahms for the 4eat.

If not, I can tell you which wires. And actually it is better to splice in to the wires at the connectors behind the passenger side kickpanel. Let's you run shorter wires and no splicing under the hood.

I see problems with your math though.

a 50% duty cycle will not yeild a very strong transfer to the rear wheels. You need to BARELY drive the solenoid to let it build pressure (or not drive it at all, via simple *cut* switch) to achieve 4WD. Operating the solenoid 50% of the time drains alot of pressure off, yeilding slip. When the TCU drives maximum 4wd, it runs the solenoid at 5%......barely draining off any pressure.

If you want to build a fancy controller to lock 4wd, but still relieve pressure, it will need to be a PWM cicruit. Simply dropping the voltage will not work, espescially when you are talking about trying to run it at the low end.

Example: you need to run it at about 5% CYCLE. 5% of 12v is not even 1 full volt. it would just do nothing to the solenoid....no operation.

you need to feed it short pulses of 12v, not just grossly lowered volts.


TCM codes mean absolutely nothing....hardly a loose end. There is a pilot pressure valve that limits maximum pressure mechanically...........
Simple switch is all you need.

#12 eulogious

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Posted 30 October 2009 - 02:27 PM

LEgacy Pinouts are totally different.

Don't guess here.

If you have the an 88, 89, or 90 electrical FSM(sec 6) you DO have the diagrahms for the 4eat.

If not, I can tell you which wires. And actually it is better to splice in to the wires at the connectors behind the passenger side kickpanel. Let's you run shorter wires and no splicing under the hood.


I wasn't planning on guessing. I have a DMM that I am going to use to make sure that I get the correct wire before I start cutting. I DO NOT want to cut blindly into things and hope that it works out for the best :)

I do not have an 88,89 or 90 FSM, let alone section 6 from any year. The FSM that I have I got off of the forums. That would be FANTASTIC if you could tell me what wire to splice into, if you could include the diagram for the 4EAT I would be eternally grateful. I have been looking for that since I got the car. The turbo doesn't change anything? I don't know if it does, obviously, but it did in the legacy, so I would like to just make sure...

The location that I was going to use is directly off the TCU, well a few inches back from the connector anyways, then I have to run even less wires :grin: Under the kick panel was my second pick. I followed all the wires into that side of the car...

I see problems with your math though.

a 50% duty cycle will not yeild a very strong transfer to the rear wheels. You need to BARELY drive the solenoid to let it build pressure (or not drive it at all, via simple *cut* switch) to achieve 4WD. Operating the solenoid 50% of the time drains alot of pressure off, yeilding slip. When the TCU drives maximum 4wd, it runs the solenoid at 5%......barely draining off any pressure.

If you want to build a fancy controller to lock 4wd, but still relieve pressure, it will need to be a PWM cicruit. Simply dropping the voltage will not work, espescially when you are talking about trying to run it at the low end.

Example: you need to run it at about 5% CYCLE. 5% of 12v is not even 1 full volt. it would just do nothing to the solenoid....no operation.

you need to feed it short pulses of 12v, not just grossly lowered volts.


Yup Yup, this is why I decided to abandon the idea of a 60/40 split circuit. defcon over at rs25 already made a variable circuit, but it was alot of work, for really no added benefit, besides to say you did :) Don't get me wrong, it's sweet, but really is of no use to me, that's why I decided to just do a switch. Way easier, and if something goes wrong in the future, WAY less to troubleshoot. There really is no need to mess with the TCU that much. It does a good job as it is, just on starts in crappy weather, it sucks, kinda.

TCM codes mean absolutely nothing....hardly a loose end. There is a pilot pressure valve that limits maximum pressure mechanically...........


The TCU throwing out codes is not a big deal, I am just the type of guy who will spend 15 bucks on some resistors to prevent the errors, just because that's the way I am. The codes do no harm, but I like to mess with electronics and cars, especially when there is a How-to that tells you how to do it all, and then prevents anything from flashing at me. That's just me :grin:

I had no idea that there was a valve that limits the maximum pressure mechanically. That statement proves that this mod really doesn't do any harm to the transmission. Thanks for that! *goes away all warm and fuzzy knowing his transmission is safe*

Gloyale, thanks for your insight! I appreciate everyone elses input so far as well! Thanks!

#13 eulogious

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Posted 30 October 2009 - 03:32 PM

The flipped flopped pinouts could be caused by you looking at either the male or female side of the plug and comparing the wrong end with the diagram if this makes any sense. If you compare the two connectors side by side you can see how one is the mirror image of the other .

/12345.../ and \...54321\


That makes sense. I thought about that too. I guess then my question is where does this plug go to/come from? If the are wires coming off of the transmission into the plug, then they are backwards, if they are coming from the TCU into the plug, then they are correct. I just don't know what the view is for that plug. I guess that's why I am confused. I just made the assumption that it was coming from the transmission (I really don't know how to read wiring diagrams), not the TCU, but you know what happens when you assume...

#14 eulogious

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Posted 31 October 2009 - 07:39 AM

That makes sense. I thought about that too. I guess then my question is where does this plug go to/come from? If the are wires coming off of the transmission into the plug, then they are backwards, if they are coming from the TCU into the plug, then they are correct. I just don't know what the view is for that plug. I guess that's why I am confused. I just made the assumption that it was coming from the transmission (I really don't know how to read wiring diagrams), not the TCU, but you know what happens when you assume...


So I went ahead and pulled the connector apart to see what I was looking at, and I was looking at it wrong. The plug in the diagram goes to the TCU. It's female (DUH!) so now I know what a female connector looks like on a wiring diagram ;) That's what happens when you assume I guess. You look like an rump roast!

On a happier note, I have found the wire for the duty C solenoid :banana: And sure enough, the diagram that I have is the correct one, at least for the wire, up to that point. It changes somewhere along the way though. I ended up trimming the insulation back just enough to expose some bare wire, on the Green/Red wire in the engine bay going to the TCU, and tested it with my DMM. With the FWD fuse in place, the wires voltage is 8.6 just as expected, and with the FWD fuse removed, gear shift lever in 1st, and foot to the floor, the voltage reads .333 just as expected. YAY!! The sad news is that the wire does change color somewhere along the way. The Green/Red wire that is coming directly off the TCU, shows nothing when doing the same tests :( So now that I have found the correct wire, I am going to use the wire in the engine bay, and run wires into the car. I have to repair were I removed the insulation anyways, so I might as well use that spot to splice in. I also already have a spot to run through the firewall, since I did that while installing my boost gauge, so I will run the wire next to the boost line.

I would still like to know what color that wire is once it gets inside the car and also have a diagram that I know is the correct one. Like I said the diagram that I have says the wire doesn't change color, but the Green/Red wire on the TCU is not the duty C solenoid wire, so ya...

I will post back more after some more progress!

#15 Log1call

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Posted 31 October 2009 - 04:30 PM

Have you read that the rear wheels are driven more aggresively when you move the shift lever to first?

If you want more aggresive power to the rear, whilst still having slip when needed and no tcu trouble codes, I'd just wire the first gear indicator on all the time on the inhibitor switch.

The solenoid won't work properly with dc going into it. It's the nature of electromagnets to have more pull when they have more voltage but they still try and travel the same distance. This valve the solenoid opens is not a tapered needle that adjusts gradualy, well not very tapered anyway, so the solenoid valve is going to be very very sensitive to voltage. That's why they use a duty cycle system.

I also don't think that using a resistor is going to prevent trouble codes... the tcu will detect that the slip is not occuring between front and rear and it will set a code when it can't compenstae for the problem.

#16 Gloyale

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Posted 01 November 2009 - 12:26 PM

Under passenger side kick panel, find the Black, 20 pin connector with the TCU wires running through it (it has 2 sheilded wires in the bunch to help I.D.)

On the middle row, edge of the connector, is a Green w/ Red stripe wire.

That is the on you want.

Cut it, and splice a switch inline.

If you like, you can use a Double Pole, Double Throw(no center off)

wire the C solenoid wire through one set of poles, and run 12v to an LED that comes on when you throw the switch.

#17 grossgary

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Posted 01 November 2009 - 01:37 PM

If you like, you can use a Double Pole, Double Throw(no center off)

that's what i use.

#18 eulogious

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Posted 01 November 2009 - 05:14 PM

Have you read that the rear wheels are driven more aggresively when you move the shift lever to first?


This is true with the newer 4EAT's, basically from about 2000ish on from what I have read in the subject but I could be wrong. Mine is year 2 for the 4EAT, and it does not do this. I technically can't move the lever to first either. This might seem like an rump roast thing to say, but the cars that have a first on the gear shifter seem to have better luck than those that have a 1 hold button. I have the button :) I also tried it in a parking lot, no binding...

I also don't think that using a resistor is going to prevent trouble codes... the tcu will detect that the slip is not occuring between front and rear and it will set a code when it can't compenstae for the problem.


Haven't tried it yet, but several others have, and have had no problems. The only time you should have errors, is on start up anyway from what I have read. If you start the car with the switch on, and no resistor pack, the AT Temp light will flash 16 times or so and then stop and never flash again. Other than that, you don't get any messages/errors I believe, even without the resistor pack. I could be wrong on this, but I don't think others have had any issue with TCU codes just running a simple switch. The only reason I am doing the resistor pack is because I like electronics, and if I can prevent a problem by using simple electronics, I will. Like I said before, that's just me :grin:

Under passenger side kick panel, find the Black, 20 pin connector with the TCU wires running through it (it has 2 sheilded wires in the bunch to help I.D.)

On the middle row, edge of the connector, is a Green w/ Red stripe wire.

That is the on you want.

Cut it, and splice a switch inline.

If you like, you can use a Double Pole, Double Throw(no center off)

wire the C solenoid wire through one set of poles, and run 12v to an LED that comes on when you throw the switch.


Thanks for that! I will have to go give it a go and see what I can come up with. I already have the DPDT switch and a LED, so I am already with ya on that :grin:

So I have built the resistor pack, now all I need is some time to go out and install the actual switch into the car. Hopfeully I will have time to get out tomorrow and take a closer look at everything. I will update when I make some more progress. Thanks everyone for your help! I wouldn't have gotten this far without your help, thanks!

#19 eulogious

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Posted 03 November 2009 - 03:34 AM

Ok, so I have installed the switch and everything works perfectly :banana: I did some testing too to see if the resistor pack really managed to do anything. So I wired up my switch and all, but I left the resistor pack ungrounded to see what the TCU would do. After my successful test drive, I turned the car off, and then turned it back on, and my power light flashed 16 times. Turn the car off and then back on again, the light wouldn't flash. I then started the car, flipped the switch on and then off, turned off the car, turned it back on and got the blinking lights again. Ok, so it works, but the TCU is getting the duty C solenoid error. This is what I was expecting. I then grounded the resistor pack, and then did the same experiment again. This time I got no error codes! So the resistor pack does prevent any errors. I will post back with more pics and info on how I did it all. Thanks everyone for all the help so I could do this mod!

#20 coldfusion21

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Posted 18 November 2009 - 02:09 PM

please do report back. I am planning on doing this soon in my 90 legacy.


Trying to figure out how I am going to get the wiring diagrams though.

Can i pull the TCU plug and check for continuity from the FWD fuse to the connector and locate the correct wire?


I plan on doing a separate switch for FWD/AWD too. That way i can switch to manual mode (just like everyone else is doing with the resistor packs) and then either provide 12v (like the FWD fuse does) or nothing at all (like everyone else is doing)

#21 coldfusion21

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Posted 18 November 2009 - 02:29 PM

please do report back. I am planning on doing this soon in my 90 legacy.


Trying to figure out how I am going to get the wiring diagrams though.

Can i pull the TCU plug and check for continuity from the FWD fuse to the connector and locate the correct wire?


I plan on doing a separate switch for FWD/AWD too. That way i can switch to manual mode (just like everyone else is doing with the resistor packs) and then either provide 12v (like the FWD fuse does) or nothing at all (like everyone else is doing)

#22 eulogious

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Posted 18 November 2009 - 04:41 PM

please do report back. I am planning on doing this soon in my 90 legacy.


Trying to figure out how I am going to get the wiring diagrams though.

Can i pull the TCU plug and check for continuity from the FWD fuse to the connector and locate the correct wire?


I plan on doing a separate switch for FWD/AWD too. That way i can switch to manual mode (just like everyone else is doing with the resistor packs) and then either provide 12v (like the FWD fuse does) or nothing at all (like everyone else is doing)


If you are planning on doing this in a legacy, then follow the rs25 link in the first post and it has some links to some FSM's. I don't know if they have a 1990 legacy or not, but it will get you started. I did this on my loyale, which has a completely different pinout and every thing, so I would NOT follow my exact instructions. I believe if you read through all the pages on the rs25 forum they mention what the wire is for the legacy. I can't remember if they do or not, but you might want to check there first, you will probably have better luck.

For me, I don't see a point in wiring up a switch to activate FWD. I am not planning on trying ebrake turns or anything, so I see no point for my needs, which is why I just kept it simple. If you really want a good read, you should check out what presslab did with some paddle shifters. Search these forums for 4EAT paddle shifters, and you will be blown away by what that guy did. Seriously impressive stuff. I know my way around electronics, but not anywhere near what that guy knows.

I am still waiting on my FSM's to arrive (should be any day now), and I will post back after I have some time to do a proper write up with the FSM scans.

#23 frogstar7055

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Posted 18 November 2009 - 08:10 PM

I've done this mod and have only used it a few times.
It definitely works,instant traction front and rear.

And in first and second you get the same result but not until 75% wot.
That's why you can do circles in first without it binding like when it's locked up.

#24 coldfusion21

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Posted 18 November 2009 - 08:18 PM

If you really want a good read, you should check out what presslab did with some paddle shifters. Search these forums for 4EAT paddle shifters, and you will be blown away by what that guy did. Seriously impressive stuff. I know my way around electronics, but not anywhere near what that guy knows.



I am a volvo guy at heart and i followed one guys project where he did this to an all electronic volvo transmission, used a stamp microprocessor and now has a paddle shifted turbo volvo.


I did some thinking and the FWD isn't worth it, I agree. I can always leave my switch alone and put in the FWD fuse if i really need it.


I will look through the rs25.com stuff, but to test what they say i could check it as described with the FWD fuse correct?

#25 eulogious

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Posted 19 November 2009 - 03:55 AM

I've done this mod and have only used it a few times.
It definitely works,instant traction front and rear.

And in first and second you get the same result but not until 75% wot.
That's why you can do circles in first without it binding like when it's locked up.


I have heard this as well, but nobody has been able to confirm that this works, especially on a 1990 4EAT out of a loyale. The legacy and the loyale 4EAT transmissions use different TCU's, even when the cars are the same year, the legacy has a different TCU than the loyale or ae82 series for that matter. The legacy TCU has a better cpu in it and some other things that mine does not. I think that contributes to the confusion on what works and what doesn't. You would think that subaru would have just made one TCU for the cars and put the same one in all, but they didn't. I could be wrong when I say that the 1st gear trick doesn't work because I haven't done WOT on it to find out, but like I said, the TCU's are different so that might mean something... Either way, that's why I did the switch.

I will look through the rs25.com stuff, but to test what they say i could check it as described with the FWD fuse correct?


That's what I did to find the wire, I just grabbed my DMM and started testing wires as described in the rs25 forum until I found the correct one. Just make sure you have the TCU, not the ECU :rolleyes: I was testing the ECU at first, because the loyale puts the TCU in a different place than the legacy's. Oops, oh well...

Feel free to ask me any questions, and I will help were I can, but since I don't have a legacy, I don't know how much help I will be, but I will help as much as I can! Good luck!




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