4EAT Center Diff Lock Question

[johnceggleston]

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

 

well, if the gear selector is in 1 or 2, you get the 50/50 split. i can't see you rock crawling in "D". but then 50/50 isn't locked 4wd either.

 

i wonder if you can trick the tcu(?) into thinking you are in 1 or 2 when you are in fact in D or 3. this would give 50/50 in the snow for instance with out having to shift into 1 or 2. a plus in bad conditions, and it would engage before the wheels slipped. subaru has decided that either we don't need this advantage or it's not good for the car/trans.

 

i posted in another thread that when you select "2" you can feel the AWD engage an instant after you start rolling (slight uphill is most noticeable). you can feel a substialtial load being put on the drive train. this would imply less effeicent operation, but if you need 4wd, go for it.

[OB99W]

[...]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...

With respect to the inductive kick and related effect on the switch (or relay) contacts, it makes no difference whether the circuit is switched in the "ground" or "positive" lead.

[Soutthpaw]

With respect to the inductive kick and related effect on the switch (or relay) contacts, it makes no difference whether the circuit is switched in the "ground" or "positive" lead.

 

Thanks to everyone for contributing to this thread, it seems to be pretty informative, I am no electrical or electronics engineer so if anyone is I'm enjoying learning in this thread, I enjoy the Diagnostics and troubleshooting on a professional basis as well..

I am wondering where we can find someone with intricate knowledge on how the ECU sends a signal to the Solenoid... and why it causes the failures.... I am guessing it will be beyond most tranny rebuilders and most subaru technicians. Anyone have a good contact at SOA that might actually be able to get a definitive answer..

 

Is there anyone here who has actually had a tranny fail after doing a mod like this??? was it specifically the transfer clutch pack that failed???

[nipper]

Thanks to everyone for contributing to this thread, it seems to be pretty informative, I am no electrical or electronics engineer so if anyone is I'm enjoying learning in this thread, I enjoy the Diagnostics and troubleshooting on a professional basis as well..

I am wondering where we can find someone with intricate knowledge on how the ECU sends a signal to the Solenoid... and why it causes the failures.... I am guessing it will be beyond most tranny rebuilders and most subaru technicians. Anyone have a good contact at SOA that might actually be able to get a definitive answer..

 

Is there anyone here who has actually had a tranny fail after doing a mod like this??? was it specifically the transfer clutch pack that failed???

 

As i have said earlier, quite a few have. No one here knows the logic, just the inputs and outputs of the TCU. The signal itself is a pulse, with the ECU monitering the voltage spikes to make sure the solenid (as it does with all solenoids) is operating.

 

Granted no one has done this on a freash transmission, but with a 3500 or more gamble, ild just rather let the puter do what it is designed to do.

 

nipper

[operose]

I drove my legacy hard and far from whenever that long thread was until a couple of months ago, and if anything the transmission acted less "funny" with age.. the car is parked right now simply because I don't want to maintain it anymore??

 

I never had transmission temp light issues, either, with just a regular switch I had from something else wired in. hell, I never even soldered the wires because I forgot. they are twisted and heat shrinked.

 

 

(again, do this at your own risk.)

[MountainBiker]

if the gear selector is in 1 or 2' date=' you get the 50/50 split. [/quote']

I don't know who started this myth, but it is a myth, and I really wish people would stop propogating it.

 

Put the gear selector in 1 and turn a circle in a paved parking lot. Do you get binding? No, you do not. If you had the clutch pack fully pressurized, you WOULD get binding.

[nipper]

I don't know who started this myth, but it is a myth, and I really wish people would stop propogating it.

 

Put the gear selector in 1 and turn a circle in a paved parking lot. Do you get binding? No, you do not. If you had the clutch pack fully pressurized, you WOULD get binding.

 

The myth comes subaru, so they may know something about it.

 

AS I HAVE SAID BEFORE there is alot more to the AWD system aside from the duty c solenoid.

 

There is the solenoid.

There is an internal spool valve.

There is the clutchpack WHICH IS DESIGNED TO SLIP TO ALLOW FOR TURNS

 

You get 50/50 in reverse and low.

 

The spool valve determines the pressure, the duty c determines how the pulsing of the clutch pack.

 

Its like a light switch, the DUTY c is the on off, and spool is the amperage. At low speeds the spool vavle allows max available pressure to the clutch pack, and high speed it reduces the pressure to the clutch pack so the force is consistant to the clutch pack. The spool regulates line pressure from the tranny to the clutch pack, the c regulates the amount of split.

 

Odd, cookie and i just talked about threads like this, and why and whne i choose to bow out. i am choosing to bow out of this one. Sometimes some of these are like

 

nipper

[MountainBiker]

So if Subaru says you get a 50/50 TORQUE split in 1st gear, then you are only as good as an open diff, which also gives you a 50/50 torque split.

 

Subaru also says that we have Symmetrical AWD, and that they "transfer power from the wheels that slip to the wheels that grip". These statements aren't technically true, but they aren't outright lying either (they gotta prevent lawsuits).

[johnceggleston]

So if Subaru says you get a 50/50 TORQUE split in 1st gear, then you are only as good as an open diff, which also gives you a 50/50 torque split.

 

Subaru also says that we have Symmetrical AWD, and that they "transfer power from the wheels that slip to the wheels that grip". These statements aren't technically true, but they aren't outright lying either (they gotta prevent lawsuits).

 

i'm not sure it's a 50/50 torque split, some one some where explained the 50/50 as the duty c cycle. i'm not real sure what that means, but until we have an awd on a 4 wheel dyno and actually test it, we'll never know. but the 50/50 is an effective way to describe the difference between "mostly FWD" (90/10) and AWD (50/50).

 

except for off roading , how many have gotten a subaru stuck? or a better question, how many have driven a subaru past 6 stuck 4WD SUV's? the computer does a pretty good job making these cars go. and my experience has been, almost 200K subaru AWD miles and one 300$ awd drive repair.

 

i'm hooked. my only disappointment is that since i moved and changed jobs, i'm only driving 16K miles ayear, down from 30k. i think my car is going to rot before i wear it out.

 

do you subaru??

[idosubaru]

i don't recall any failures resulting from this modification. can we link to actual threads or will someone post about failures? i haven't had any and i've actually done this mod years ago and know others that have actually done it as well. my experience is mostly with first gen 4EAT's in the XT6 which never have torque bind, DS C, or clutch pack failure. the newer gen 4EAT's have these issues no matter if you play with the wiring or not! do a search and see all the threads that come up....without any switches being installed.

 

more interesting is that the first gen 4EAT's (like in the XT6) experience far less issues with TB and other clutch pack/duty solenoid C issues. actually i can't recall any in my history of owning 15, working on others, being on the XT6 boards for like a decade. being older and more prone to have been abused they should experience more issues...but instead they have none?

 

the TCU is not adequate for my usage and does hinder functionality for me, so there's no need to debate whether or not this mod is necessary, that's rediculous.

[Andyjo]

i don't recall any failures resulting from this modification. can we link to actual threads or will someone post about failures?

 

Gary, Mine blew up.... well... the switch burnt out, locking it on the highway... i didn't realize it until i got about... 270 miles... i believe someone else had their switch burn out too... i think if you're going to do it, you may have to use a relay... which might reduce your chances of having a switch burnout... then locking it up.. and trashing your tranny :-\

[idosubaru]

that does suck, but that's not failure due to normal and intended useage though. if i improperly install subaru plug wires and they give a CEL right away, i don't say that Subaru wires cause problems. not saying you installed anything wrong but the mod failed, either wiring, connections or the switch wasn't up to the task? i just used an off the shelf radio shack switch. i used it once for about 50 miles, but that was in some serious doo-doo of the white variety, no road to speak of.

 

i have a light installed so i can see it light up if it's accidentally hit (which has happened). so i can turn it off. i thought about wiring in the manual XT6 diff lock button since it would look stock, but went against that notion because it's so easy to accidentally turn it on.

[nipper]

its a very low voltage ciruit. The awd fuse powers the C solenoid so it is on and locks out AWD. Cutting the power to the duty c gives you max pressure 50/50 awd. This is why the clutches fry up. At max pressure you get very little slip in the clutchpack, so when they have to slip they chew themselves up. The duty c not only affects the balance of f/r awd, but also the pressure to the clutch pack via a spool valve in the hydraulic circuit.

 

nipper

[idosubaru]

well put nipper. i would think it goes without saying that's certainly not a toy, very rarely needed by most people and i even rarely use it. normally the TCU does do a fine job. when i do use it, it is needed and i'm always on ice, snow, mud, streams. the worst is low speed or sitting in very slick/steep terrain where the intial spinning (just before TCU detects slip and does anything about it), starts a rut or sliding that you don't want. in those kinds of conditions it is very helpful. or when pulling someone out of snow/mud, for the same reasons you don't want to even start slipping, as you won't have the traction to get them out. of course i'll try first without it in those situations, stop and lock up if necessary.

[MountainBiker]

I take a different approach, I use the switch proactively. When I'm offroad and I'm coming up on something that looks sketchy, I flip the switch before I enter the section.

 

Right after I did this mod a couple years ago, I would leave it on for long periods of time (50 miles or more) when offroad. Now I engage it in sand and mud, and for other sketchy sections uphill and downhill. I try to flip the switch off when I come up on tight turns, in order to lessen the strain on the clutch pack.

 

And like I've said before, I don't get a TCM warning/MIL light.

[nipper]

I take a different approach, I use the switch proactively. When I'm offroad and I'm coming up on something that looks sketchy, I flip the switch before I enter the section.

 

Right after I did this mod a couple years ago, I would leave it on for long periods of time (50 miles or more) when offroad. Now I engage it in sand and mud, and for other sketchy sections uphill and downhill. I try to flip the switch off when I come up on tight turns, in order to lessen the strain on the clutch pack.

 

And like I've said before, I don't get a TCM warning/MIL light.

 

you dont get a light because the "failure" corrects itself. You only get a light if there was problem on the last time the car was on. If the problem corrected itself it wont show the fault.

 

nipper

[MountainBiker]

you dont get a light because the "failure" corrects itself. You only get a light if there was problem on the last time the car was on. If the problem corrected itself it wont show the fault.

 

nipper

Actually, I don't get a light because of the resistors. Before I had those in place, I did get a light. In fact, Andy and many others have also reported getting the light whenever they used the switch.

 

I also don't get a light, even if I leave the switch in the locked position when I shut off the car and remove the key, and then restart.

 

I don't get a light, because with my setup, the TCM cannot tell what I'm doing. As far as it "knows", it is still controlling the transfer clutch solenoid. That is what one of the resistors is for, a dummy load that mimics the transfer solenoid.

 

BTW, anyone notice the buzzing you get from the transmission when in R,1,2,3, or 4? Open your driver's door with the engine running and you'll hear it. Then place the selector in P or N, and the buzzing slowly goes away. That buzzing noise is the transfer clutch solenoid!

[nipper]

Actually, I don't get a light because of the resistors. Before I had those in place, I did get a light. In fact, Andy and many others have also reported getting the light whenever they used the switch.

 

I also don't get a light, even if I leave the switch in the locked position when I shut off the car and remove the key, and then restart.

 

I don't get a light, because with my setup, the TCM cannot tell what I'm doing. As far as it "knows", it is still controlling the transfer clutch solenoid. That is what one of the resistors is for, a dummy load that mimics the transfer solenoid.

 

BTW, anyone notice the buzzing you get from the transmission when in R,1,2,3, or 4? Open your driver's door with the engine running and you'll hear it. Then place the selector in P or N, and the buzzing slowly goes away. That buzzing noise is the transfer clutch solenoid!

 

never heard it, i went out and listened for it, and mine doesnt buzz.

 

nipper

[MountainBiker]

never heard it, i went out and listened for it, and mine doesnt buzz.

 

nipper

Maybe it's just the later models then, or maybe I'm sensitive to the frequency. I've heard it on all Foresters from 2001-2005

[Wayne Boncyk]

never heard it, i went out and listened for it, and mine doesnt buzz.

 

nipper

 

Maybe it only buzzes with this resistor setup? Mine has never buzzed either.

[nipper]

Maybe it only buzzes with this resistor setup? Mine has never buzzed either.

 

the resistor is making it buz. Apply a resistor in line with a duty solenoid, or almost any solenoid and ti will buzz (not fully engage). On the plus side this may be why he is not chewing up his clutch pack. he als is cycling the solenoid much faster then the TCU does, so he is allowing for the plates to slip like they should.

Maybe he has found the holy grail

 

nipper

[Wayne Boncyk]

the resistor is making it buz. Apply a resistor in line with a duty solenoid, or almost any solenoid and ti will buzz (not fully engage). On the plus side this may be why he is not chewing up his clutch pack. he als is cycling the solenoid much faster then the TCU does, so he is allowing for the plates to slip like they should.

Maybe he has found the holy grail

 

nipper

 

Yeah - makes sense. Not sure how much AWD you'd really be getting with a setup that doesn't fully engage the solenoid, though.

[nipper]

Yeah - makes sense. Not sure how much AWD you'd really be getting with a setup that doesn't fully engage the solenoid, though.

ssssshhh dont tell mountainbiker that

 

nipper

[porcupine73]

Oh is that what that buzzing noise is? I hear it on '00obw with key in run (but engine not running) and shifting the AT gear selector. Maybe since it's pumping no ATF at the time the sound is more audible.

[MountainBiker]

You people don't understand. The buzz is 100% not related to the resistors I've added. The buzzing is in stock vehicles and mine too, because my TCM thinks it is stock. Like I said, maybe my ear is sensitive to this frequency, because I hear it on all the 4EATs I've come across.

 

BTW, my 4wd works so good (when I've engaged it) that if I try to make a u-turn, even on dirt, I grind to a halt due to binding. When I make tight turns in sand, I get massive understeer. It doesn't get much better than that.

 

I'm not trying to force anyone to do this, and there are risks involved, especially for those that don't engineer a good system. With the proper design, install and use, transfer clutch life can be extended, and offroad capability can be improved.