Torque Bind, FWD Fuse, and the Duty Solinoid

[RallyKeith]

Since I'm now trying to absorb as much info on the automatics I've been reading all the threads on Torque Bind and people who think they have it. My question is this:

 

How does the clutch pack for the center diff work as far a fluid/pressure presence vs lock up?

 

I assumed that the clutch pack is locked until fluid/pressure is presented. This would explain how the FWD fuse works and why you can't tow with two wheels on the ground. Putting in the fuse would send a full signal to the duty solinoid allowing full fluid/pressure to the clutch pack and thus un-locking the diff.

 

So my beef is this, if you have a car that is exhibiting torque bind, and putting in the FWD fuse gets rid of it, then how can the problem be the duty solinoid? By putting in the fuse and having it go away, that to me means the solinoid is working.

 

This however then raises the question that if putting in the FWD fuse and applying full signal to the duty solinoid does infact open the diff, then to me the problem is not with the diff itself or the duty solinoid, but something else or maybe even the TCU that is supposed to be telling the diff to open.

 

Thoughts? Am I way off on how I think the diff works? Please help me (and the rest of us) Learn!

 

Keith

[All_talk]

Hey Keith

 

The rear drive clutch pack is open with no pressure applied, but the duty solenoid works opposite of what you’d think, it applies full pressure at low voltage and no pressure at full voltage. So the FWD fuse puts full voltage to the solenoid and removes the pressure from the clutch pack.

 

From what I have read there are two common causes for torque bind, In the older (pre ’97 I think) the tail shaft runs directly in the aluminum tail housing without bearings, and once worn it can bind or ratchet in the housing. The second is the failed (or failing) duty solenoid “C” which leaves you locked in AWD. If installing the FWD fuse removes the torque bind then the solenoid is good and the problem is something else.

Here's a pic of the clutch pack and solenoid C, more pics inside the 4EAT here:

http://photobucket.com/albums/v204/All_talk/Subaru/4EAT/

 

 

Gary

[friendly_jacek]

Nice pictures!

 

I'm no mechanic but from reading the forum, there are 2 more possibilities (and potentially even more):

Dirty ATF causing sticking of the clutch pack (this appears to be a common one).

Scored clutch pack casing friction and draging (damage from eneven tires, etc).

[Legacy777]

Just to clarify....there is no center diff on the automatics. All of the rear power transfer is handled in that rear extension housing. The clutch packs and everything is powered using line pressure from the pump.

 

As mentioned, with the duty c solenoid full open or unplugged completely, the rear is getting full line pressure, (aka 50/50 torque split). Inserting the FWD fuse causes the solenoid to close all the way causing no power to go to the rear wheels.

 

Another clarification....you can NOT use the FWD fuse on the automatics to tow the car with just the rear wheels on the ground. In fact, you can NOT tow an automatic car with the drive wheels on the ground. Lubrication is provided by the pump, which is driven off the engine. So if you have an AWD automatic, all four wheels MUST be off the ground.

 

Regarding what causes torque bind....yes there are some issues with transmission, but I'd say the majority of the issues span from infrequent ATF fluid changes.

 

If you really want to extend the life of an AT, change the fluid often, (more then what the owner's manual recommends), use good synthetic fluid, and add a trans cooler.

[982.5GT]

I drive a 98 2.5 Legacy, w/ AT

 

If I "fixed" my torque bind with an AT flush + conditioner, and continue to maintain the car (keeping tires even, good alignment, and continuing to flush the AT fluid every 30,000 miles), then can I still expect the TCU or the duty c solenoid to go at some point too?

 

 

Just to clarify....there is no center diff on the automatics. All of the rear power transfer is handled in that rear extension housing. The clutch packs and everything is powered using line pressure from the pump.

 

As mentioned, with the duty c solenoid full open or unplugged completely, the rear is getting full line pressure, (aka 50/50 torque split). Inserting the FWD fuse causes the solenoid to close all the way causing no power to go to the rear wheels.

 

Another clarification....you can NOT use the FWD fuse on the automatics to tow the car with just the rear wheels on the ground. In fact, you can NOT tow an automatic car with the drive wheels on the ground. Lubrication is provided by the pump, which is driven off the engine. So if you have an AWD automatic, all four wheels MUST be off the ground.

 

Regarding what causes torque bind....yes there are some issues with transmission, but I'd say the majority of the issues span from infrequent ATF fluid changes.

 

If you really want to extend the life of an AT, change the fluid often, (more then what the owner's manual recommends), use good synthetic fluid, and add a trans cooler.

[All_talk]

Just to clarify....there is no center diff on the automatics. All of the rear power transfer is handled in that rear extension housing. The clutch packs and everything is powered using line pressure from the pump.

 

I may be reading this wrong but it sounds like you are saying the rear wheels are driven hydraulically driven?

 

Not true, the inner shell is attached to the end of the main output shaft, the rear wheels are mechanically driven by the same shaft as the front wheels, the line pressure only engages the clutch pack.

 

But yes, there is no center diff, the 4EAT is like a FWD trans with a PTO to drive the rear.

 

Gary

[RallyKeith]

All Talk: thanks for the pic, but I already had one of these apart and saw everything myself. Playing with the clutch pack I could see that with no pressure it was "open" and would require pressure to lock-up. However, It does seem that I had the duty solenoid's operation backwards.

 

But, for the record, can we agree that if putting the FWD fuse in stops your torque bind that the problem is not the Duty Solenoid?

[All_talk]

But, for the record, can we agree that if putting the FWD fuse in stops your torque bind that the problem is not the Duty Solenoid?

 

Yes

 

Gary

[Legacy777]

I drive a 98 2.5 Legacy, w/ AT

 

If I "fixed" my torque bind with an AT flush + conditioner, and continue to maintain the car (keeping tires even, good alignment, and continuing to flush the AT fluid every 30,000 miles), then can I still expect the TCU or the duty c solenoid to go at some point too?

 

It's probably not too likely they'll go too, but who can say for sure.

[Legacy777]

I may be reading this wrong but it sounds like you are saying the rear wheels are driven hydraulically driven?

 

Not true, the inner shell is attached to the end of the main output shaft, the rear wheels are mechanically driven by the same shaft as the front wheels, the line pressure only engages the clutch pack.

 

But yes, there is no center diff, the 4EAT is like a FWD trans with a PTO to drive the rear.

 

Gary

 

Technically, both front and rear wheels are hydraulicly driven

 

I wasn't clear, hydraulic pressure engages/disengages the clutch packs which causes power to be sent to the rear wheels

[kummer]

my post from a diff forum. apply the same.

 

my car does that. so would you go so far to say that mine is unplugged? with out coding??? and how would it come unplugged on its own??? whats my issue? i have read torque bind = trans flush. fwd fuse= does nothing. duty solenoid “C”??? = where do i buy one. i want to know. what is most likely to fix this??? i cant pay and arm and leg hunting it down! oh and it also does it backing up. 187,XXX miles 1995 2.2 LX

 

▼▼▼▼ info from other site▼▼▼▼

 

 

there are 3 large connectors on the rear of the engine passenger side where it meets the trans. the largest goes to the trans. if you unplug it you will put the car in ''limp'' mode, 3rd gear only, and it should lock it in 4WD. if you drive it in tight slow circles you should feel, binding jumping, or bucking, like a 4WD truck with locked front hubs on dry pavement. if it does this then the mechanical parts are good, i think.

[johnceggleston]

i have read torque bind = trans flush. fwd fuse= does nothing.

 

so you have torque bind? and the fuse provides no change?

 

does the FWD light come on with the fuse in place?

 

does your AT TEMP light flash 16 times at start up? (does it come on with all the other lights in the ''on'' position just before you turn it to start?)

 

lots of times this condition is caused by dirty fluid so a drain and fill may help. you can do it yourself, just like an oil change. doing it 3 times with driving in between (~1 gallon of fluid each fill.) will change out most of your old dirty fluid. MAKE SURE you know which is the ''trans '' drain plug and dip stick. there is also a front differential drain plug and dip stick.

 

if your AT Temp light is not flashing when you start the car, then the computer thinks the duty c is still ok. but if the FWD light does not come on with the FWD fuse in place then the duty c is not working. this assume your AT Temp and FWD warning light are working properly.

 

what is happening with your car??

[jimkasper2]

Doing a search on torque bind, here are my symptoms-

 

98 Outback Automatic about 68,500 miles. Bought used at about 35,000. Have done two drain and fills on trans and differentials since I bought it, using Mobil One synthetic fluids. Last time about 65,000 miles, two times drain and fill on tranny.

 

No check engine lights or flashing transmission light. Car is currently driven sparingly, about 3,000 miles a year, country driving.

 

Torque bind started about 8 months ago. More pronounced turning right. Put fuse in, FWD lights up, no flashing transmission light, and torque bind gone.

 

I guess I will have to have it diagnosed, but any thing else I should tell the service guys? I hate to go in naked.

 

Jim

[mrtoyou7747]

98 OB 225000

I changed the duty solenoid at about 100K. Do they go bad again?

 

I was told that the reason for the torque bind was that the Duty C solenoid had a design defect that was fixed with subsequent parts. Is this true?

 

I am remiss in changing the tranny fluid could this be the problem?

[WoodsWagon]

If the duty C goes bad, the a/t temp light will flash 16 times when you start the car.

 

If the fluid is dirty, putting in the FWD fuse will make the bind go away. Change the fluid 3 times with a bit of driving in between each change.

 

If the bind doesn't go away with the FWD fuse in but the a/t temp light isn't flashing, you may need to replace the clutchpack as the tabs sometimes wear into the splines of the drum and get jammed.

[mrtoyou7747]

The 98 is an OBDII vehicle does the A/T light still flash with a problem?

 

Is there a danger in having the transmission "flushed"

[johnceggleston]

The 98 is an OBDII vehicle does the A/T light still flash with a problem?

the AT Temp light flashes at start up when there was an electrical fault on the LAST drive cycle. it will also flash with SOME obd2 trouble codes, but not all. just a few.

 

Is there a danger in having the transmission "flushed"

drain and fill is considered safer, and it is easy, just like doing the engine oil. you should do it 3 times with driving around the block in between. the trans holds about 10 qts. and a drain it only produce about 3.5 - 4 qts.

[petronews]

Hi everyone, BIG thanks for the info I was getting from you so far, it is invaluable. Sorry if i missed any "Hello" topic to introduce myself properly, but right now my mind is set to a different puzzle that I am eager to solve, would You like to help.

 

What I have:

1) 1997, 4eat naturally aspirated 2.5l Subaru Legacy Outback with rear lsd.

2) new selenoid C

3) new clutch pack

4) new ATF

4) torque bind
5) the infamous 16 flashes of "power" – right after starting the engine

6) inserting a fuse does nothing – no fwd light comes on, MPT remains locked (except this morning, before driving the car, when everything was fine)

7) voltage in the fwd fuse socket shows 5.5 Volts (that's low, innit?)

 

The rest of the riddle:

 

I lost AWD about a month ago, and drove the car with the FWD fuse installed and a FWD light on the dash for about 300km since then – came back from where I noticed problems and drove it to the shop for repair last week. The car was fine in FWD. At the shop I removed the fuse, and the dash light came off.

 

The mechanic found out that the tail housing must have been previosuly repaired and put together with glue instead of a gasket. Previous owner had a massive ATF leak and the car was repaired by subaru unexpierienced shop close to the highway.

 

My mechanic found the clutch packs worn out completly, and described it as "MPT fubar". There was a lot of steel shavings in the fluid. 

 

Somehow he figured the selenoid C is also blown, as there was no reaction of it after plugging it to the 12V battery.  

 

He replaced both the selenoid C and the entire MPT set, properly minding the important issues of measurment and order of installation.

 

He got the entire inside well cleaned from the bits, put everything together and gave it new ATF.

 

He didn't change the filter, He didn't measure the line pressure nor did he check the FWD fuse operation.

 

During a test run he noticed the binding problem and when i arrived to pick the car he suggested me to drive home (100km) and see if it goes away. He was hoping that the binding is caused by left over steel shavings that will eventually flush.

 

I did about 10kms and turned around as I didnt feel comfortably with the binding. I installed the fuse and to my big suprise noticed that it does nothing. As it was late at night, I went to my friends and made an appointment with the mechanic in the morning. The next morning I was even more confused – as I turned the ignition, the FWD light was ON, and the car was FWD. I removed the fuse and discovered the binding problem was gone. All puzzled and helpless I decided to give it a test – I drove the car in various conditions for the next hour, including climbing steep snowy slopes and making fast highway runs and the problem came back, leaving me and my mechanic completly clueless. I went home and started to investigate. 

HELP! I cannot measure the pressure line myself and I was unable to read trouble codes – i didnt find the connector to ground pins and the secret handshake did not work. Any clues, ideas?

[CNY_Dave]

The FWD fuse grounds a signal from the TCU, signalling the TCU to please apply +12V to the transfer solenoid (duty C solenoid).

 

On my '03 if the trans light is flashing the TCU ignores the FWD fuse, and if the fault clears while driving the FWD fuse does nothing until the car is shut off and re-started.

 

I do know the valve the duty C solenoid operates (the solenoid is actually a valve itself) depends on very clean fluid, as there are some pinhole-sized feed/bleed ports. The valve has it's own filter.

 

If random bad things happen, could be the filter is missing or the valve has crud in it that will never flush out because the holes are so small.

[johnceggleston]

sometimes the TCU can cause issues. there have been reports of the circuit boards having scorch marks. but just a part not working when HOT , even with no scorch marks seems possible.

 

i had a 95 lego L auto that had an intermittent issue. when it got TB i put the fuse in. some times the fuse would work and somnetimes it wold not. some time the FWD lite was on and sometimes it was off.

 

two possible causes, either the TCU or the duty C is intermittent.

 

i vote TCU, unless you doubt your mrchanics ability.

Edited March 21, 2013 by johnceggleston

[petronews]

CNY_Dave, are you sure the fuse doesn't override the TCU?
johnceggleston, i agree, but why would the problem develop after replacing clutch pack and duty C… I didn't expierience the bind before losing the rear, the fwd fuse was operational and TCU didn't flash anything before the repair. Right now I doubt in my mechanic ability as much as I do in new parts reliability as the easiest answer would be faulty duty C selenoid. That's why I am asking about the correct voltage in the FWD socket. Faulty wiring could be the problem, too, or shorted mass.

 

Could You please measure voltage in the Your fwd sockets?

Edited March 21, 2013 by petronews

[eulogious]

What CNY_Dave said is correct.  The FWD fuse plugs into the tcu, and the tcu then enables FWD.  The fuse does NOT bypass the tcu.

 

If your duty c was bad for a long time, it could have actually destroyed the transistor in the TCU itself, making the TCU not work right.  I have 3 tcu that have a bad duty c.  So this is a "fairly" common thing.  It might have worked for a while, then for some reason installing the new solenoid blew it.  Or your mechanic fried the tcu.  Hard to say.  BUT I would replace the TCU and see where it gets you.  They are cheap in the yards.  Just make sure the TCU you get comes out of a car with the same gear ratio as yours.  Wrong TCU might cause weird issues.

 

Oh, and the voltage will be either 0 (grounded) or 12v+ (I forget on the older models which way it is, on my 1990 leggy its 12v+) for the FWD fuse.  Anything else means you gots an issues with your wiring...

Edited March 21, 2013 by eulogious

[CNY_Dave]

Since the signal from the TCU to the FWD fuse is from the TCUs microcontroller, at some point it could have gone to 5V on that pin instead of 12V, or it could indicate a pretty severe current drain in the TCU.

 

The TCU is easy to pull, pop the top off and take a look at. Some are repairable, a bad track can be replaced by wire, a bad driver can be replaced with one scavenged from another TCU, my '03 has several drivers of each type. Also, I found a chip that IO used to build my inverting one that could be used to replace one of the drivers, but you'd have to finagle a way to keep the 'sense' line happy, the driver chip incorporates a line that the microcontroller looks at to make sure the solenoid line isn't shorted or open.

[petronews]

Thanks guys, blewn TCU would explain a lot. The other day I wanted to measure the TCU harness and connectors and check with the service manual charts, but i really couldn't tell where that damn TCU is. My car is LHD, I found the ECU under the passanger feet floor, but no sign of TCU under the steering column…  I found the lpg computer. Is the TCU big? I'll try it again. 

[CNY_Dave]

TCU on my left-drive is a metal box that sits above and left of the brake pedal.

 

Two connectors plug into it, right next to each other, one white and one grey on mine.