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Centre diff lock on AWD auto


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175 replies to this topic

#126 Fatz

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Posted 05 January 2006 - 07:23 PM

i think it is a 95 gearbox could possibly be 96. Twin turbo box, 4 speed auto..What else is needed?
Thanx all

#127 grossgary

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Posted 06 January 2006 - 06:50 AM

are you sure it's AWD? if it's AWD and has a duty solenoid C then you just need to find the Duty solenoid C wiring.

as a last resort crawl under the car and look at the very rear of the transmission, the extension housing that the rear driveshaft is connected to. there should be two sets of wires, one for the rear speed sensor and one for duty solenoid C, i think those are the only wires on the very rear of the transmission. if you can post a picture we can tell you which wire(s) are for Duty solenoid C and you can splice into it there. pretty sure the speed sensor is more *top mounted* and the duty solenoid is on the side sort of. but i'm not positive. the speed sensor might be dead center on the top and hard to find/see but it's been awhile since i've looked at an auto trans.

let us know what you see on your rear extension housing...

#128 subeman90

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Posted 06 January 2006 - 08:04 PM

********** this subject is in the USRM now. I put andyjo's post in about the mod with the pics too. Enjoy and thanks again to Andyjo. ***************

#129 Fatz

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Posted 07 January 2006 - 08:12 PM

hey all i got centre diff lock now:)
all that i had to do was put a fuse in the carrier under the hood, on the car the engine and gearbox came out of, it says 4wd, on my lseries bay, it says fwd, so i never thought of trying it, then someone suggested it to me and it works.... Im over the moon..
cheers all

#130 theletteri

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Posted 08 March 2007 - 03:06 PM

sorry to bring up such an old thread....

i MUST do this mod to my 06 OBS! i have tried on 2 occasions to find this "duty solenoid c" wire but i have come up with nothing. i have the service manual for my car (on CD) and there is nothing about this part. the only thing that i found close to it is a "lock solenoid" or "locking solenoid". would this be the right part? can i even do this to an 06? i cant even find the solenoid wire in the wiring diagram.

any help would be appreciated!

here is my baby

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#131 Manarius

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Posted 08 March 2007 - 04:03 PM

I doubt that your Impreza has the 4EAT, therefore things would be a lot different between technology from ten years ago and now.

#132 Andyjo

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Posted 08 March 2007 - 07:55 PM

Get an oscilliscope... and start tapping into wires while driving... :rolleyes:

#133 Gloyale

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Posted 08 March 2007 - 09:25 PM

I doubt that your Impreza has the 4EAT, therefore things would be a lot different between technology from ten years ago and now.


Any Automatic impreza sure as heck does have as 4eat if it is automatic. Unless it is a 5eat?
And look for "transfer clutch" solenoid.

#134 Gloyale

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Posted 08 March 2007 - 09:39 PM

hey all i got centre diff lock now:)
all that i had to do was put a fuse in the carrier under the hood, on the car the engine and gearbox came out of, it says 4wd, on my lseries bay, it says fwd, so i never thought of trying it, then someone suggested it to me and it works.... Im over the moon..
cheers all


That must be an Australia thing. That fuse puts the US cars into FWD

#135 nipper

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Posted 08 March 2007 - 09:43 PM

That must be an Australia thing. That fuse puts the US cars into FWD


Austrailia has a differn AWd setup then we do i think. i know the austrailian SVX's are nothing like the US ones as far as the tranny is concerned. So it may be possible he doesnt have a solenoid like we do (if the car is austrailian).

nipper

#136 theletteri

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Posted 09 March 2007 - 02:21 PM

thanx for the help guys!

it is a 4eat. i found the 2 plugs that are mentioned in the write-up but i don't have one that is 4x4... it is 5x4. i am going to map out what ones are grounds and then test the others to them and see if i can get ~13ohms on one of them.

i don't have an o-scope nor the ability to drive and test the wires :eek:

i will keep you all posted on my progress.

i also spoke with a subaru specialist up in Sacramento and he is familiar with this mod but he has not seen it done on such a new one. he figures that the 5x4 plug would be the right one...:headbang:

#137 nipper

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Posted 09 March 2007 - 02:32 PM

Hey all, i have a auto AWD series 3 Gen 2 TT box out of a 95?, and i want to make it have selectable centre diff lock, yet i have no idea how to do so.
Has anyone done one of these before?
A mate told me that you have to do something like this...

You need to supply 12v to the Duty C solenoid in the centre diff and it will lock like a selectable box.

Is there anything else involved? Where do i find the solenoid??

Cheers guys.
Fatz
P.S im not sure if matters change seeings that this it a aussie car, if anything is different or not:confused:


So we all missed it. you want to cut the power to the Duty C solenoid, not hold it open. Holding the solenoid open is the same as putting the FWD fuse in the holder. It dumps all the pressure to the clutch pack so you get zero rear wheel drive.

nipper

#138 cookie

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Posted 09 March 2007 - 03:15 PM

shhhh, he was happy.

#139 nipper

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Posted 09 March 2007 - 03:43 PM

shhhh, he was happy.


:clap: ;) :cool: :headbang:

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#140 Gloyale

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Posted 09 March 2007 - 06:40 PM

So we all missed it. you want to cut the power to the Duty C solenoid, not hold it open. Holding the solenoid open is the same as putting the FWD fuse in the holder. It dumps all the pressure to the clutch pack so you get zero rear wheel drive.

nipper



It has a similar effect, but is not really the same. The FWD fuse cicuit carries no power(perhaps mV) it is a signal wire to the TCU. When you insert the fuse it connects that terminal of the TCU to ground and "tells" it to send max power (95% Duty cycle) to the Solenoid. That power is output from a different terminal. The power for the solenoid does not run through the FWD fuse circuit.

12v wired straight to solenoid has the same effect of fully energizing the Solenoid. But it doesn't and should not be made to have anything to do with the FWD fuse. I have a feeling that reports of "fried switches" from this mod are a result of some version of mis wiring like this.

Not trying to say you're wrong Nip, just clarifying. Better Clarity is always good for the forum.

#141 nipper

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Posted 09 March 2007 - 08:05 PM

It has a similar effect, but is not really the same. The FWD fuse cicuit carries no power(perhaps mV) it is a signal wire to the TCU. When you insert the fuse it connects that terminal of the TCU to ground and "tells" it to send max power (95% Duty cycle) to the Solenoid. That power is output from a different terminal. The power for the solenoid does not run through the FWD fuse circuit.

12v wired straight to solenoid has the same effect of fully energizing the Solenoid. But it doesn't and should not be made to have anything to do with the FWD fuse. I have a feeling that reports of "fried switches" from this mod are a result of some version of mis wiring like this.

Not trying to say you're wrong Nip, just clarifying. Better Clarity is always good for the forum.


i was giving the readers digest version (i have fully explained it many many many many times). Sometiems i get tired of repeating myself ... and getting :Flame: for critisizing the switches.

Actually it fully energizes the solenoid. This dumps all the pressure, so there is zero torque applied to the rear wheels. The switch to the C solenoid does the opposit, which puts the car in full unmodulated 50/50 lockup.

so this time you can be the target :-p

(that and im sick with an apendix that can't make up its mind what it wants to do)

nipper

#142 Gloyale

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Posted 09 March 2007 - 10:26 PM

i was giving the readers digest version (i have fully explained it many many many many times). Sometiems i get tired of repeating myself ... and getting :Flame: for critisizing the switches.

Actually it fully energizes the solenoid. This dumps all the pressure, so there is zero torque applied to the rear wheels. The switch to the C solenoid does the opposit, which puts the car in full unmodulated 50/50 lockup.

so this time you can be the target :-p

(that and im sick with an apendix that can't make up its mind what it wants to do)


nipper

[

12v wired straight to solenoid has the same effect of fully energizing the Solenoid. But it doesn't and should not be made to have anything to do with the FWD fuse. I have a feeling that reports of "fried switches" from this mod are a result of some version of mis wiring like this.


I think you are misunderstanding this statement. I was trying to address what people have said about the lock switch. I am trying to say you should not be running 12v to anywhere to do it. except maybe for an indicator light through a dp/dt switch. then I mention the FWD fuse because it is related, and some people have talked of trying to incorporate it in the mod. It is a seperate cicuit. 2nd way to effect the same thing, but not the same.

I know what the lock switch does, I have it. It interupts the Solenoid wire= no volts. I know what the Fuse does aswell. I have a seperate switch mounted inside, wired with spades going into the connector, with a fuse inline for convieniece. It's a seperate switch and circuit still though. It won't however function if the "lock" switch is open, interupting the solenoid wire. I get it. I am just being clear that the FWD fuse circuit should never be given power. And that the Solenoid Circuit should never be wired to ground. They are two circuits that interact but are not actually connected. One signals the other.

And really I am not trying to Flame. :Flame: I newbed it with the "elite master" thing way back but I really am not on here to fight:mad:

I am here cause I love to see more people driving old subes:)
and to pick to death old threads the OP isn't even reading Probably:lol:

Short version:

IE: DON"T WIRE THEM TOGHETHER!

#143 johnceggleston

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Posted 01 April 2007 - 01:37 PM

not to :horse:, but i had a thought about how to creat a switch that wouldn't throw a code or hurt your trans if left on. the down side to this idea is that i don't think it will "lock" your AWD into 4WD. at best it would give you 50/50 split and still allow for slipping / speed differential between front and rear.

question / idea:

instead of actually controlling the power / signal to the duty c, why not control the signal FROM the rear speed sensor. letting the TCU think the rear wheels aren't turning will fully ingage the rear wheels (50/50 split) and still allow for some slipping which will prevent damage. of course if you just disconnect the speed sensor you may get a code for that, but i bet you could put some kind of resistor on the circuit to prevent that. if you were really creative , you could use something that would allow a varible setting. you could actually adjust the power split.

anyway, just a thought.

#144 nipper

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Posted 01 April 2007 - 02:19 PM

not to :horse:, but i had a thought about how to creat a switch that wouldn't throw a code or hurt your trans if left on. the down side to this idea is that i don't think it will "lock" your AWD into 4WD. at best it would give you 50/50 split and still allow for slipping / speed differential between front and rear.

question / idea:

instead of actually controlling the power / signal to the duty c, why not control the signal FROM the rear speed sensor. letting the TCU think the rear wheels aren't turning will fully ingage the rear wheels (50/50 split) and still allow for some slipping which will prevent damage. of course if you just disconnect the speed sensor you may get a code for that, but i bet you could put some kind of resistor on the circuit to prevent that. if you were really creative , you could use something that would allow a varible setting. you could actually adjust the power split.

anyway, just a thought.


Well the speed sensor is a square wave. No resistor would help there. 50/50 power split is difffernt from full lock. 50/50 on demand would be great. Wht someone needs to do is throw a three channel scope on the two wheel sesnosr and on the duty C solenoid and see how they all interact. From there we could make a pulse generator of some kind and dial in the amount of 4wd we want.

nipper

#145 Gloyale

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Posted 01 April 2007 - 07:17 PM

I think johnceggleston might be on to something. Nipper is correct that th square wave generated by the rear speed sensor is not replicaple by a resistor. However the sensor does have a simple resistance value, and placeing a resistor of that value in it's stead would make the TCU think it was still there. It wouldn't see a wave from it, so it would assume rear driveshaft speed as zero. I am not sure how this would affect the TCU's control of the split? I guess I'll have to try it. Too bad all the snow is gone for a real test. I'll have to go find some mud!

#146 nipper

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Posted 01 April 2007 - 07:59 PM

I think johnceggleston might be on to something. Nipper is correct that th square wave generated by the rear speed sensor is not replicaple by a resistor. However the sensor does have a simple resistance value, and placeing a resistor of that value in it's stead would make the TCU think it was still there. It wouldn't see a wave from it, so it would assume rear driveshaft speed as zero. I am not sure how this would affect the TCU's control of the split? I guess I'll have to try it. Too bad all the snow is gone for a real test. I'll have to go find some mud!


If the mismatch between the two axles is too high for two long, the TCU will disconnect the AWD. Also if there is no pulse it assums the 2nd sensor is dead and disables the AWD.

nipper

#147 johnceggleston

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Posted 02 April 2007 - 03:44 PM

If the mismatch between the two axles is too high for two long, the TCU will disconnect the AWD. Also if there is no pulse it assums the 2nd sensor is dead and disables the AWD.

nipper


every time you turn around good ol' subaru figures a way to protect us from ourselves. and once again, if they designed it to cut out the AWD if the difference in speed is too great, then there's a reason for it.

i don't know square waves from ocean waves, but it would be nice if only 60 or 70% of the pulses got to the tcu.

based on someone's alternate front speed sensor (his speedo drive gear in the front diff failed) you could put and alternate sensor on the drive shaft / axel with only 3 magnets instead of 4. that assumes they are the same type of speed sensor and the it could be mounted. and of course that it wouldn't damage the car.

regarding the TCU disconnecting the rear wheels: at start up , and this is a long shot, maybe the TCU would fully ingage the rear for lower speeds and then disengage at some point. if the tcu disconnect the AWD unit when would it come back on line, at next start up or whan the speed deceases.??

i think im' lost, where's the remote.?

#148 the_postie

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Posted 03 April 2007 - 01:56 AM

Not to0 sure what you guys are up to.I can tell ya that power up the duty c in tt box,this box is vtd different to the awd clutch pack normally found in 4eat,fully locks the rear but in a standard 4eat unlocks.This box{vtd }you can spin the rear wheels while the front is braked.Lock the back in and it behaves almost like a rear wheel drive car.On road you can have no input to the rear transfer[speed sensor dissconnected] and it behaves like open centre diff front to rear,like a range rover box.The vtd extension can be added to a standard 4eat box but requires a different tcu or a bit custom electrical work.These are great offroad espically with a 3000 rpm stall:burnout:Even if you don't lock the rear it will go most places.

#149 Gloyale

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Posted 07 April 2007 - 01:05 PM

Not to0 sure what you guys are up to.I can tell ya that power up the duty c in tt box,this box is vtd different to the awd clutch pack normally found in 4eat,fully locks the rear but in a standard 4eat unlocks.This box{vtd }you can spin the rear wheels while the front is braked.Lock the back in and it behaves almost like a rear wheel drive car.On road you can have no input to the rear transfer[speed sensor dissconnected] and it behaves like open centre diff front to rear,like a range rover box.The vtd extension can be added to a standard 4eat box but requires a different tcu or a bit custom electrical work.These are great offroad espically with a 3000 rpm stall:burnout:Even if you don't lock the rear it will go most places.


Wish we had that option in the states. But honestly, simply cutting power to the C solenoid works great to lock the rear. It does excactly the same thing in terms of clutch operation as putting an old PT auto into 4wd. Full pilot pressure to the clutch packs. There is still a mechanical(spring loaded) drain in the transfer valve. Turbo PT tranny's had almost 300 psi going to the clutches. 4eat max line pressure is around 235 psi. The "switch" method works great.

#150 nipper

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Posted 07 April 2007 - 01:11 PM

every time you turn around good ol' subaru figures a way to protect us from ourselves. and once again, if they designed it to cut out the AWD if the difference in speed is too great, then there's a reason for it.

i don't know square waves from ocean waves, but it would be nice if only 60 or 70% of the pulses got to the tcu.

based on someone's alternate front speed sensor (his speedo drive gear in the front diff failed) you could put and alternate sensor on the drive shaft / axel with only 3 magnets instead of 4. that assumes they are the same type of speed sensor and the it could be mounted. and of course that it wouldn't damage the car.


i think im' lost, where's the remote.?


Its not magnets Square wave ius just wht it is, its square. The TCU knows that the waves are supposed to be X degrees apart, if it sees anything else its going to assume that the signal is faulty and act accordingly.

You need 100% of the pulses to get to the tcu, just at a slower pace.

nipper




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