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4EAT Center Diff Lock Question


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57 replies to this topic

#1 Soutthpaw

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Posted 09 October 2006 - 10:49 AM

I need to know how solinoid C is activated. I already know the wiring diagram but can't find out if it is activated by voltage or by varying resistance. also what are the values for the solonoid when it is fully enganged and when it is fully disengaged. if it fails the tranny is supposed to go into full AWD lock-up. So am i correct to assume if it was unplugged it would default to full lock-up

#2 Andyjo

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Posted 09 October 2006 - 11:25 AM

The solenoid is controled by a a Pulse width modulation signal. but yes, if you get rid of that signal (cut the wire, put a stich in it, etc..) it will throw the car into "4wd" mode, or pretty much torque bind. So yeah, the failure mode is locked up.
If you wanted to make a varying control on the diff (change your front/back split) you would have to have some 555 timers, to create your signal, and then a pulse width modification system to alter how much the solenoid plays...
make sense? ;)
more info in putting a switch in there: http://www.ultimates...ead.php?t=50264

I need to know how solinoid C is activated. I already know the wiring diagram but can't find out if it is activated by voltage or by varying resistance. also what are the values for the solonoid when it is fully enganged and when it is fully disengaged. if it fails the tranny is supposed to go into full AWD lock-up. So am i correct to assume if it was unplugged it would default to full lock-up



#3 Soutthpaw

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Posted 09 October 2006 - 05:31 PM

Ok I was reading that link before I asked the question. basically if i put a switch in which is normally closed (when off) if I turn it to ON it will create the 4 wd mode correct?
Does that trigger any OBD codes??

I am not sure why you need to pull a ground of Pin 4? why cant you just use a spst swich in line (series) with the #11 wire?

Thanks for the article by the way. I got a center diff lock swich from the junkyard out of a 88GL 10 I can use that. I pulled up the wiring diagram for the 88 to see what the configuration of the switch is it has built in illimunation, and depending which 2 wires i use it can be normally open or normally closed in the off position.

DJ

#4 NorthWet

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Posted 09 October 2006 - 05:35 PM

...I got a center diff lock swich from the junkyard out of a 88GL 10...

Did you check to see if the LSD was still under that GL10???

#5 Soutthpaw

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Posted 09 October 2006 - 05:47 PM

Did you check to see if the LSD was still under that GL10???



Nope, but its still at the local self serve junk yard. which years had LS diffs, what were the gear rations and do the Outbacks have LS? if not can they be swapped over??? I am in Colorado so there are usually 5 to 10 of the old Subarus in the local yard at any given time ... there is about 3 xt6's there now. the 2 door coupe one... not sure I got the model name right prob at least 5 wagons and a few sedans as well as a couple of the old early 80 wagons.

#6 OB99W

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Posted 09 October 2006 - 07:24 PM

[...]more info in putting a switch in there: http://www.ultimates...ead.php?t=50264

Two of the pics didn't show when I tried the link; URLs that I found work correctly are:
http://www.ultimates.../10420conv2.jpg
http://www.ultimates.../10420conv7.jpg

On the other hand, those shots may not be the most important. ;)

#7 NorthWet

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Posted 09 October 2006 - 07:31 PM

The (early) LSDs were all 3.70 (except the mysterious, oft-mentioned but never-documented XT6 3.90), available as an option on any EA82-ish Subaru (87 and later???), most commonly found on turbos, and almost certainly on a vehicle with a locking center-diff. The diff tag quite clearly identifies it as an LSD.

#8 nipper

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Posted 11 October 2006 - 12:44 AM

Ok I was reading that link before I asked the question. basically if i put a switch in which is normally closed (when off) if I turn it to ON it will create the 4 wd mode correct?
Does that trigger any OBD codes??

I am not sure why you need to pull a ground of Pin 4? why cant you just use a spst swich in line (series) with the #11 wire?

Thanks for the article by the way. I got a center diff lock swich from the junkyard out of a 88GL 10 I can use that. I pulled up the wiring diagram for the 88 to see what the configuration of the switch is it has built in illimunation, and depending which 2 wires i use it can be normally open or normally closed in the off position.

DJ

word to the wise, almost everyone that seems to put this switch in within a year blows thier clutchpack. There is more to the AWD unit aside from the duty C solenoid. There is also an internal spool valve that plays a part in this. That is controled by the duty c and internal tranny pressure.

i strongly dont recomend this switch.

The switch will trigger the tranny temp light on the next start.

Why do you want this switch anyway? the TCU does a very good job at operating the awd.

nipper

#9 Andyjo

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Posted 11 October 2006 - 07:47 AM

word to the wise, almost everyone that seems to put this switch in within a year blows thier clutchpack. There is more to the AWD unit aside from the duty C solenoid. There is also an internal spool valve that plays a part in this. That is controled by the duty c and internal tranny pressure.



Almost everyone gets a burnt out switch too, which causes a lockup... the switches burn out because (from what i'm thinking) is that the signal is just too strong for it. (ie too much amperage), even though i was running a 30A switch.. it still managed to fry itself. :-\

#10 johnceggleston

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Posted 11 October 2006 - 08:26 AM

i wonder if the "no power/fully locked" causes less fluid to flow as a lubricant and that helps cause damage to the clutch pack.??

Almost everyone gets a burnt out switch too, which causes a lockup... the switches burn out because (from what i'm thinking) is that the signal is just too strong for it. (ie too much amperage), even though i was running a 30A switch.. it still managed to fry itself. :-\


i'm not sure, there aren't many things that pull 30 amps. and from what i saw, this duty c isn't one of them. some one recently wrote a fairly technical description of the "signal" to the duty c, it didn't sound high amp to me.. i'd be interested to read the elec. spec, for a new one. but i doubt it's printed on the back of the box.

#11 Hocrest

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Posted 11 October 2006 - 08:39 AM

I'm no electrical genius, but if this was drawing enough power to fry a 30 amp switch, why doesn't it fry the 18-20g(?) wire that it feeds through?? Anyplase else where the engineers are expecting a high load, they are using a heavier wire???

It seems like something else is going on???

#12 Wayne Boncyk

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Posted 11 October 2006 - 10:23 AM

Well, in the case of my Duty C, putting a fuse in the FWD socket causes about 0.7 amps to flow in that line, which is probably a control circuit in the TCU rather than the drive to the Solenoid itself. I don't get how you can fry a 30 amp contact switch with this signal... unless it really is to the solenoid, and there's a heck of a flyback kick (i.e. a sharp rise in voltage that happens when you rapidly open an inductive load) when the switch is thrown.

#13 MountainBiker

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Posted 11 October 2006 - 11:44 AM

word to the wise, almost everyone that seems to put this switch in within a year blows thier clutchpack. There is more to the AWD unit aside from the duty C solenoid. There is also an internal spool valve that plays a part in this. That is controled by the duty c and internal tranny pressure.

i strongly dont recomend this switch.

The switch will trigger the tranny temp light on the next start.

Why do you want this switch anyway? the TCU does a very good job at operating the awd.

nipper

Yes, do this mod at your own risk!

However, I've been using a switch and a set of resistors since January '05, with no problems. My setup is not quite the same as Andyjo's, it's a little more complex to prevent the dash light and to provide a soft bleed of voltage on the solenoid. In that time, I've only gotten the tranny temp light twice, and it wasn't on the next start, it was right after resuming AWD.

Why do it? To eliminate the delay in transferring power to the rear wheels in tough situations, to get 4wd on deceleration, and to save the clutch pack when driving on sand (TCU significantly slips the clutch when on sand).

#14 Soutthpaw

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Posted 11 October 2006 - 02:40 PM

Almost everyone gets a burnt out switch too, which causes a lockup... the switches burn out because (from what i'm thinking) is that the signal is just too strong for it. (ie too much amperage), even though i was running a 30A switch.. it still managed to fry itself. :-\


No way is that solinoid pulling even close to 30 A

#15 Soutthpaw

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Posted 11 October 2006 - 02:44 PM

Yes, do this mod at your own risk!

However, I've been using a switch and a set of resistors since January '05, with no problems. My setup is not quite the same as Andyjo's, it's a little more complex to prevent the dash light and to provide a soft bleed of voltage on the solenoid. In that time, I've only gotten the tranny temp light twice, and it wasn't on the next start, it was right after resuming AWD.

Why do it? To eliminate the delay in transferring power to the rear wheels in tough situations, to get 4wd on deceleration, and to save the clutch pack when driving on sand (TCU significantly slips the clutch when on sand).


So do you want to share with us how you set up that switch with resistors. I am thinking of putting the car up on jack stands and then hooking my lab scope to the duty solinoid to see what is really happening with that solinoid.

I dont think it is a voltage spike causing the switch to burn out because we are not dealing with high voltage like in a secondary ign where you need a condenser or something to handle the power surge.

I was looking on Alldata, I am thinking based on their diagram showing the intended operation of the solenoid that the reason trannys are failing is that folks who do this mod are using it on hard surfaces for cornering. It probably needs some slippage as the solenoid normally decrease the duty cycle in cornering.

#16 MountainBiker

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Posted 12 October 2006 - 11:55 AM

So do you want to share with us how you set up that switch with resistors.

No problem. I had posted a link on the super-long diff lock thread from earlier this year, but I just checked, and it looks like my linky is dead.

Here is a new link to a post with the updated schematic. Check out the link that says MtnBiker, and I can vouch for the non-turbo setup working very well:
http://www.subarufor...18&postcount=66

If people are interested, here is a link to my trials and tribulations of trying to design this thing:
http://offroadsubaru...viewtopic&t=686

DISCLAIMER:
While I believe this mod to be safe when used correctly, use it at your own risk. If any thing harmful happens to you, your car, your possessions, innocent bystanders Posted Image, or passengers, don't blame me, this forum, or anyone else but yourself!


#17 Andyjo

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Posted 12 October 2006 - 01:26 PM

DISCLAIMER:
While I believe this mod to be safe when used correctly, use it at your own risk. If any thing harmful happens to you, your car, your possessions, innocent bystanders Posted Image, or passengers, don't blame me, this forum, or anyone else but yourself!


I agree.
and just a note: a brand new 4EAT runs about 4000 bucks...

#18 nipper

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Posted 12 October 2006 - 05:35 PM

So do you want to share with us how you set up that switch with resistors. I am thinking of putting the car up on jack stands and then hooking my lab scope to the duty solinoid to see what is really happening with that solinoid.

I dont think it is a voltage spike causing the switch to burn out because we are not dealing with high voltage like in a secondary ign where you need a condenser or something to handle the power surge.

I was looking on Alldata, I am thinking based on their diagram showing the intended operation of the solenoid that the reason trannys are failing is that folks who do this mod are using it on hard surfaces for cornering. It probably needs some slippage as the solenoid normally decrease the duty cycle in cornering.


your close. Not only does the duty c regulate the application, but the spool valve regulates how much force is applied to the clutch pack.

Example:
The duty C (easy numbers) pulses 30 times in 60 seocnds to give you 50/50 split. The spool vlave regulates how much force is applied to those clutches depending upon line pressure. I am not sure if this is an inverse relationship. This would be a function of engine RPM, as the engine drives the pump. The digram ive seen is not really clear on this function. This function mechnaical (hydraulic) and not electrical. It operates in cunjunction with the Duty C. There may ebven be a balancing act, since the duty C is more directly related to this spool valve then the clutch pack itself.
The bleed off of the Duty C is probably the magic potion thats missing to make a switch work.
The FWD fuse is just a signal to the ECU.

nipper

#19 Wayne Boncyk

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Posted 13 October 2006 - 12:18 PM

Ah, Nip! Now I get it!! I was confused -- these guys really ARE putting a switch in-line with the Duty C solenoid itself, not with that TCU point off the FWD switch.

HMMM -- I can see why you could eventually fry any mechanical switch that you might put in series with the solenoid. This solenoid cct is perfectly capable of applying a back EMF (voltage) of several times the DC voltage needed to hold the solenoid "ON," when it is abruptly disconnected. The solenoid is driven by a solid-state PWM control, probably a power FET. That circuit also probably has enough damping built in that it can handle the transients that the coil of the solenoid throws back its way when it turns off... but if the cct is interrupted at an arbitrary point in time, while that FET is still turned ON for example, the switch contacts that are doing the interrupting are likely to see both the current from the FET driver and a current spike resulting from the induced high voltage on the line resulting from the electric field collapsing as the solenoid is de-energized. Instantaneous currents of many amps could be possible in such a case -- they only last microseconds, but that would be enough to melt switch contacts.

Putting resistors in the loop can limit those high instantaneous currents, but they will also muck with the duty cycle of the solenoid, and that might contribute to premature failure of the solenoid istelf.

A little electrical engineering knowledge is truly a dangerous thing! I am only guessing at an explanation that makes sense; I could know if this is for sure the reason that switches and solenoids fail if I could see a schematic of the real circuit.

#20 nipper

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Posted 13 October 2006 - 12:49 PM

Ah, Nip! Now I get it!! I was confused -- these guys really ARE putting a switch in-line with the Duty C solenoid itself, not with that TCU point off the FWD switch.

HMMM -- I can see why you could eventually fry any mechanical switch that you might put in series with the solenoid. This solenoid cct is perfectly capable of applying a back EMF (voltage) of several times the DC voltage needed to hold the solenoid "ON," when it is abruptly disconnected. The solenoid is driven by a solid-state PWM control, probably a power FET. That circuit also probably has enough damping built in that it can handle the transients that the coil of the solenoid throws back its way when it turns off... but if the cct is interrupted at an arbitrary point in time, while that FET is still turned ON for example, the switch contacts that are doing the interrupting are likely to see both the current from the FET driver and a current spike resulting from the induced high voltage on the line resulting from the electric field collapsing as the solenoid is de-energized. Instantaneous currents of many amps could be possible in such a case -- they only last microseconds, but that would be enough to melt switch contacts.

Putting resistors in the loop can limit those high instantaneous currents, but they will also muck with the duty cycle of the solenoid, and that might contribute to premature failure of the solenoid istelf.

A little electrical engineering knowledge is truly a dangerous thing! I am only guessing at an explanation that makes sense; I could know if this is for sure the reason that switches and solenoids fail if I could see a schematic of the real circuit.


well they have too. The FWD fuse sends a signal to the TCU to power the duty c (hold it open) so the AWD is disabled. In order to get AWD on demand, you need to interupt that circuit between the TCU and the solenoid. The rest of your argument is valid.

nipper

#21 OB99W

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Posted 13 October 2006 - 04:18 PM

[...]Here is a new link to a post with the updated schematic. Check out the link that says MtnBiker, and I can vouch for the non-turbo setup working very well:
http://www.subarufor...18&postcount=66

If people are interested, here is a link to my trials and tribulations of trying to design this thing:
http://offroadsubaru...viewtopic&t=686

I'd look, but it seems that registration is required, and I really don't need the temptation af another forum to post on. :)


... but if the cct is interrupted at an arbitrary point in time, while that FET is still turned ON for example, the switch contacts that are doing the interrupting are likely to see both the current from the FET driver and a current spike resulting from the induced high voltage on the line resulting from the electric field collapsing as the solenoid is de-energized. Instantaneous currents of many amps could be possible in such a case -- they only last microseconds, but that would be enough to melt switch contacts.[...]

Not having seen the circuit, I can't be sure, but Wayne's explanation for the problem seems logical. Perhaps proper application of damper/snubber diodes might be the solution, but I'm not willing to do the design and then depend on a disclaimer to protect my hide. :D

For non-EE's, interesting reading, may or may not be applicable (and a 1N4004 probably isn't the best choice for usage with the "C" duty solenoid):
http://www.oz.net/~c...ivekickback.htm

#22 Wayne Boncyk

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Posted 13 October 2006 - 04:37 PM

I'd look, but it seems that registration is required, and I really don't need the temptation af another forum to post on. :)


Not having seen the circuit, I can't be sure, but Wayne's explanation for the problem seems logical. Perhaps proper application of damper/snubber diodes might be the solution, but I'm not willing to do the design and then depend on a disclaimer to protect my hide. :D


THAT'S why I didn't offer up a design! ;)

For non-EE's, interesting reading, may or may not be applicable (and a 1N4004 probably isn't the best choice for usage with the "C" duty solenoid):
http://www.oz.net/~c...ivekickback.htm


Definitely it's applicable - better than I could've written myself!! But you're right, the choice of diode needs to be made after you know the characteristics of the coil; I'd use an appropriately valued zener if I were really trying to do this. Personally, I'm with Nipper on this thread - given that the solenoid and the mechanical valve interact in a complex manner to put just the right amount of coupling out to the rear end, I'd be wary of anything that disabled only part of the system until I knew what effect that action would have on the rest of the system.

#23 Hocrest

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Posted 13 October 2006 - 05:26 PM

Probably a better way to engage a "Diff Lock" is to determine what signals the TCU to engage a 50/50 split. And then figure a way to cheat that??

#24 nipper

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Posted 13 October 2006 - 05:42 PM

The AWD is basically controleed by the differntial in front and rear axle speeds, along with selecting low gear, reverse or wide open throttle. This leaves the option of a signal generator in one of the wheel speed senors.
reproducing WOT will cause too many issues, and so will selecting low.
If you cut out the VSS you loose awd completly. If there is more then a 50 mph differential between front and rear AWD cuts out.

nipper

#25 Soutthpaw

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Posted 14 October 2006 - 07:40 PM

Probably a better way to engage a "Diff Lock" is to determine what signals the TCU to engage a 50/50 split. And then figure a way to cheat that??


That is what I was getting at when I started the thread, thanks for putting it in simple terms


I read that link on inductive kickback... based on that diagram you would need to inturrept the ground side of the switch. however if you interrupt the Pos side, you are creating a break before the solenoid so the problem of wearing it out would not apply... Also it does not explain why people who are using this mod are killing their clutch packs.
I think what is happening is that constantly locked-up fluid is not getting between the clutch pack friction surfaces. they are drying out or overheating and burning up. The cause would be driving too agressively or too long with the Lock-up on. I would use it mainly for slow speed crawling when needed. AWD is better for snow and icy roads than 4wd anyway. Wish I had the Traction control option... oh that s another thread




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