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  #1  
Old 02-23-2004, 08:46 PM
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UberRoo UberRoo is offline
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No AWD - rear wheels not engaged. Duty solenoid C? TCU?

I'm just hoping someone has had a similar experience and can advise me. My transmission has been functioning flawlessly for the last 116k miles, but has suddenly lost it's ability to use the rear wheels. I have a latent trouble code 25, "Engine torque control signal" but have had no current trouble codes whatsoever.

As I understand it, when duty solenoid C fails, you're basically stuck in '4WD' as it may be. In my case, the opposite seems to be true. I don't have a wiring diagram that details the transmission, but I do have a pinout of the transmission wiring harness connector. I don't entirely trust the pinout, but I did a basic continuity test of duty solenoid C based off the information I have and it seems to have low resistance, which indicates that it works. Additionally, both electrical failure and seizure of the valve should trigger trouble code 24. The valve seems good - why isn't it being triggered?

Has anyone else had their AWD stop working? Where can I find a complete wiring diagram of the transmission? Frankly, the solenoid is relatively easy to replace and not outrageously expensive, but I don't believe it's at fault in this case. I simply want to know how to test it with certainty without removing it - that, and to find the real problem at hand.

See the attached diagram. Any ideas?
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File Type: jpg svx_duty_solenoid_c.jpg (107.2 KB, 275 views)
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  #2  
Old 02-23-2004, 10:34 PM
gl1674 gl1674 is offline
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UberRoo,

There was some limited experience with duty solenoid A/C failures
on this site. What we've seen that solenoids wear out internal valves - the electrical resistance remains the same, they still make
clicking sounds and they *seem* to open and close fluid passage properly when tested with compressed air. However once installed in the car, the combination of fluid pressure and any duty signal from TCU (even 10% duty is enough), they will open fully and remain open all the time.

The only test that works is the ATF pressure test. There is a test port in the extension housing that provides transfer line pressure.

In your particular case the other possible culprit is the transfer clutch. If you want to test it, you need to plug an ATF pressure gauge to the test port see if you have pressure and if it behaves properly with throttle changes. However the fastest (and the best long term) solution is simply to replace both the solenoid and the transfer clutch plates.
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  #3  
Old 02-23-2004, 11:59 PM
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UberRoo UberRoo is offline
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Yesterday all was well. Today, nothin'. The rear end was clearly working very well yesterday. Today when I jack all four wheels off the ground, only the front wheels turn even if I romp on the gas.

I'm leaning away from the transfer clutch theory and here's why:

If I unplug the transmission harness, as expected I'm locked in 3rd gear, probably have 100% line pressure, and *should* have 4WD - especially with 0% duty cycle. I think it's unlikely that the transfer clutch has simply worn out - with zero load, the rear end should still spin the wheels even with a wasted clutch. I think that a pressure test will only confirm that I have no pressure going to the clutch. Am I overlooking something?

I believe that the duty solenoids A, B, and C, are designed to cycle like crazy and return to home when no signal is applied. The shift solenoids 1, 2, (and 3,) do no cycle except when shifting and will return to home only under hydraulic pressure if there is no signal. The possibility that a duty solenoid might get stuck is a new idea. How or why does this happen? Does the solenoid itself wear out or is it something else?

So I guess my question is, how do I test the solenoid? Like I said, I *think* I tested it but I don't have any solid information to work from. What wires control the solenoid? I found the harness connector underneath the throttle body (and the TCU under the dash.) To get the solenoid to "click," just apply 12v DC to it? Which pins? Is it polarity sensitive? Anyone? Wiring diagram or pinout please? (I can't believe this isn't a FAQ.)

...I'd rather crawl around with an electrical probe than put 'er up on a lift...

Thanks...
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Last edited by UberRoo; 02-24-2004 at 12:11 AM.
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  #4  
Old 02-24-2004, 12:42 AM
gl1674 gl1674 is offline
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The duty solenoids get the 50Hz duty cycle. With ignition on and engine off you can hear them buzz as you change throttle position. You probably need to put the car into garage and open windows. I'm not sure which ones you can hear.

Yes it is just 12volts. Polarity is positive of course. The other end of the solenoid is connected to the chassis/ground.

A fluid passage blocked with a small piece of clutch material or metal debris would explain your symptoms. Sorry I don't hand the manual at hand, but typically how Subaru does valve bodies is they have a small calibrated passage from the line pressure to the chamber connected to the solenoid. If the solenoid is open, it drains the pressure in the chamber to the sump and allows continuous fluid flow around the solenoid and through the calibrated opening. if the solenoid is closed, the pressure builds up. My point is that a grain of sand is enough to block the calibrated passage and once it is there, it is likely to stay there.

Where I'm getting at, electrical connections and wiring are much easier and more pleasant to play with, but the best chances to get it fixed is with the hard to reach and messy hydrolics.

It may turn out that cleaning the extension valve body is all you have to do. However you may need new gaskets that nobody stocks, don't expect it to be one day job.

In my own case I had solenoid A go at 154k miles - It would jump wide open and stay wide open. An "autopsy" did not show anything broken inside. The moving parts had obvious wear, but nothing broken in half...

Do get it fixed ASAP - don't drive without AWD. You risk too much load on the front diff (can break) and more damage to the transfer clutch/bearings in transfer case due to oil starvation - no transfer pressure means no lubrication there.
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  #5  
Old 02-24-2004, 05:53 AM
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svx_commuter svx_commuter is offline
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Hi
I had this problem with the SVX AWD, no RWD.
The transfer valve was stuck so no pressure went to the plates.
No codes and the clutch plates were fine.
A check on the transfer pressure in the extension housing will point this out. The threads are straight and not an NPT but a 1/8 npt fitting can be retapped to the metric size.
There are a few pictures in my locker.
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  #6  
Old 02-24-2004, 06:28 AM
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So would intermittent AWD seem to be a worn transfer clutch then?
And how bad a job is it to replace this?
How bad are the parts prices?

Mine has taken to lighting the front wheels up occasionally if I'm leaving from and incline in the wet, etc. You can hear the rear wanting to engage, and other times all 4 engage fine.

Thanks!
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  #7  
Old 02-25-2004, 01:01 AM
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UberRoo UberRoo is offline
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Looks like you guys are right-on about it being a mechanical problem. I sweet-talked the guys at my local dealership and they let me thumb through their service manuals (See attachment.) I found the pinouts and wiring diagrams and tested it.

The TCU puts out the correct voltage for all situations (with ignition on and in drive, less than 0.5volts with the throttle open and 8v-14v with the FWD fuse installed regardless of throttle position.) The solenoid also reads ~12ohms which is also good.

I found a quiet place and could hear the solenoid "buzzing" when in drive with the ignition on - which goes away when you apply throttle (or put in the FWD fuse which presumably stops cycling the solenoid and just sends it constant voltage.)

The factory service manuals really don't help much with trouble-shooting mechanical problems, however, in a Subaru technical training manual I got from a friend, another possibility is discussed.

From the training manual:
*******************
"Torque bind caused by seized MPT [multi-plate transfer?] clutch.

The MPT Clutch can become seized due to excessive slippage caused by Teflon seal rings, which are pinched and split from a previous repair for a different complaint/procedure. The latter complaint of binding may have been preceded by a complaint of no 4WD application. This would only be noticeable in conditions that would have required 4WD to keep the front wheels from breaking loose.

1. The "POWER" light does not flash upon start up indicating a probable mechanical failure.

2. Installation of the front wheel drive fuse makes no difference.

3. The Select Monitor [external diagnostic computer?] shows normal operation of 4WD duty. However, there is a code for speed sensor "1" in memory due to the fact that some wheels slippage had occurred when the MPT clutch had been slipping before it seized. A quick check of both speed sensors as compared to the speedometer all show approximately the same speed.

4. MPT clutch pressure checks show lower than specifications.

5. A resistance check of the duty solenoid "C" circuit shows that the circuit is complete and the solenoid is within resistance specifications.

6. Disassembly of the transfer housing reveals an overheated and seized MPT clutch. In addition, the Teflon seal rings are pinched, cut, and deformed."
*******************

Michael Blue, this section of the training manual may particularly interest you. Intermittent AWD sounds symptomatic of this problem. Maybe - maybe not. You might read the symptoms closely and see if they describe your problem.

svx_commuter, what was the solution to the stuck transfer valve? Did something just need cleaning or was replacement necessary? (I'm wondering if might be able to agitate a sticky part and flush the system. Wouldn't that be nice?)

As for me, I doubt the article apples, but my loss of 4WD might be an omen that my MPT is about to seize. In either case, sounds like I'm gonna have to crack 'er open. ...darn...
Attached Images
File Type: jpg solenoid_c_wiring_diagram_small.jpg (313.2 KB, 240 views)
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Last edited by UberRoo; 02-25-2004 at 01:20 AM.
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  #8  
Old 02-25-2004, 01:45 AM
Paxton71
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I just fixed this on mine last night.

I just got back from the test drive.

I had broken the transfer clutch hub off of the reduction gear.

SubaFreak kindly sent me some used Legacy parts to fix it. I saw the legacy parts are also wearing where I broke the hub off of my gear. (the stamped steel hub is welded to the top reduction gear.)

There is a thrust bearing that seems to spin against the clutch hub instead of against itself. Mine broke on a remanufactured 1994 trans so I'm not sure of the milage. I'm guessing 90,000 miles are on the 1994 tranny in my 1992 car.

I had intermittant 4x4 for a week then FWD. No codes ever flashed. (OK VSS when I spun the rear axle by hand with the fronts stopped triggered a code, but that was with the car up on jackstands after it was decidedly broken)

I really hope this isn't your problem too. You'll know when you take the transfer case off the back of the tranny. The broken hub is easy to spot. Sol. C is easy to test. clutch disks are easy to remove and measure.

Good luck.
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  #9  
Old 02-28-2004, 11:14 PM
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UberRoo UberRoo is offline
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Oh yeah. Snap! The clutch basket broke right off the gear. Upon close inspection, it appears that the basket was "resistance welded" to the gear. (Similar to spot welding.) You can clearly see that the basket wasn't completely bonded because where it wasn't bonded, the basket just peeled away and the casting texture of gear is apparent. A manufacturing defect if you ask me.

So, I threw the basket and gear on the lathe and spun off all the mashed metal. Everything else looks pretty good except for a thrust bearing race, but it looks serviceable. I just finished building up the basket with my welder. (I'm taking a break.) Next I gotta align it with the gear and weld it on. I'm sure you all think I'm crazy. We'll see I guess.

****************

Update: Welded the clutch basket to the gear, installed the gear back on the shaft, the transfer clutch, and threw it back in the tranny. Now all I gotta do is button it all up and put some fluid in it. Oh yeah, and test drive it.

Photos:
http://www.subaru-svx.net/photos/user.php?UberRoo
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Last edited by UberRoo; 02-29-2004 at 01:20 AM.
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  #10  
Old 02-29-2004, 03:51 AM
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UberRoo UberRoo is offline
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I HAVE AWD!!!! My ego is the size of Texas right now. Ever smile 'til it hurts? Yeah. That feeling.

Now comes the real test: Longevity. I tore out of my driveway shooting gravel out the back until I hit the pavement with a series of small but satisfying chirps. I did this a dozen more times, with all four wheels clawing away. I'd have to put some thought into being more abusive than that. I think she'll hold captain.

The timing of this was good too. The ATF needed a change anyway. Once again I'm pleased with Subaru's engineering because sadly, the hardest part of this was getting one of the oxygen sensors unscrewed.
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