Torque Bind? - Subaru Outback - Subaru Outback Forums
 
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post #1 of 5 (permalink) Old 11-11-2012, 07:54 PM Thread Starter
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Torque Bind?

1998 Outback Automatic, 180,000km. She’s been dealer maintained (I’m tired of working on cars outside in winter) and has been through two major services. A couple of years ago I was getting symptoms which I now think are torque binding - need a bit of throttle getting in or out of tight spots. The inboard rear wheel skips a bit when turning tight on a loose surface. I mentioned it to the dealer - they put in additive (maybe helped a bit), then suggested I try to avoid tight turns!

After reading through several threads here, and some excellent system descriptions (thanks!), I tried the FWD fuse. That seems to make no difference other than turning on the FWD light. The inside rear wheel still skips on gravel. If I understand correctly, the duty c should be activated full time, thereby stopping power transfer to the rear wheels which obviously isn’t happening.

Could this maybe just be an electrical problem with the duty c solenoid? Where is the solenoid on a ’98 and can I put a meter on the connector?

The ATF looks clean on the dip stick and she doesn’t get ridden hard or pull a trailer. I imagine the major servicing has replaced it before, although I don’t know how thoroughly. Should I try the aggressive ATF flushing anyway in the hopes that the issue is a gummed up valve or sticky clutch?

What about the inside rear wheel skipping - is that likely an unrelated problem with the rear diff?

One more thing... I just read elsewhere here that "when the shifter is in 2, the trans will start in 2 and stay in 2. it will not start in 1 or shift up to 2 and the rear wheels are at maximum power ~60 / 40 split, front and rear." As it happens, my car spends much of its time going up and down a long, steep, windy hill in a residential area, so it spends a lot of time in 2nd to maximize power uphill and braking downhill. Could that be causing any of this?
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post #2 of 5 (permalink) Old 11-12-2012, 08:24 AM
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When the fuse is installed, the AWD transfer clutch should remain disengaged, with no effective connection between the transmission output and the rear drive train.

If there were a short, or open, circuit between the transmission control module and the AWD solenoid (duty C), the on-board diagnostics should pick this up, and cause the AT Oil Temp light to flash. So: With the key at ON but the engine not started, does the AT Oil Temp light come on and go out when the engine is started and does it flash at any time, or stay on after the engine starts?

If the rear wheel skips when turning on loose surfaces with the FWD light showing, it could be that power is still being transferred to the rear drive, or it could be a binding rear differential. The first can be better detected if the car is on a slippery surface, where the front wheels can be made to slip when going straight (e.g. slippery upward slope). If the AWD is disabled, the rear wheels shouldn't spin (whereas when the AWD is working, if one or both front wheel spins at least one rear wheel should spin as well). If the AWD clutch is still (incorrectly) engaged, the rear wheels (also on the slippery surface) will tend to spin as well. (You will need one or more extra people to watch the front and rear wheels to be sure of what is actually happening -- don't depend on sensing this from the driver's seat.)

If the rear wheels spin even with the FWD indicator, then the AWD clutch is not disengaging. This could be caused by a malfunctioning solenoid or transfer valve (they work together) or mechanically binding transfer clutch plates. The first can be verified by checking the hydraulic pressure being sent to the clutch. There should be a port on the side of the transmission extension case for this, but I don't have details for the 1998 transmission. If the pressure remains high when the fuse is in, then the problem is clearly the solenoid. If the pressure is low, then the problem is probably mechanically binding clutch plates. In any event, it means taking down the extension case and replacing the solenoid and possibly the clutch.

If the rear wheels don't spin with the fuse in when going straight on a slippery surface, yet one rear wheel skips when the car is in a tight turn, the problem could well be in the rear differential.

Have you owned the car from new? If you're not sure if the ATF was changed, then doing multiple changes with some running in between could work (if the problem is related to the fluid or gummy deposits) and would be worth a try.

There is no fixed, preset AWD clutch engagement in manually-selected gears. The rate at which the AWD clutch pressure is increased in response to various parameters such as the throttle position and engine load is more rapid in the lower gears (1 and 2), but there's no gear in which the power to the rear is maximized at all time.

Using second gear when starting off on a slippery surface is often recommended for both MT and AT cars of all makes. The reason is that in second gear, less torque is being applied to the wheels because of lower transmission torque multiplication, and this lessens the tendency for the wheels to break loose and spin.
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post #3 of 5 (permalink) Old 11-12-2012, 03:18 PM Thread Starter
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Thanks much plain OM. I bought the car with about 90,000 km on it and immediately had a major service done. Got another done at about 170,000 km (along with heads and water pump to cure an overheating problem).

Makes sense about the diagnostics picking up an electrical fault if there was one. The AT Oil Temp light is on steady with the other idiot lights when I turn on the ignition, but all go out within a couple of seconds of starting - no flashing at any time. Also, spending a lot of time in 2nd doesn't sound like it would be likely to have caused torque bind (I thought if the clutch was at high pressure a lot of the time that might have helped cause sticking).

I'm fairly sure that power is still getting to the rear wheels with the FWD fuse in because in a tight turn on loose gravel, I can make the inside rear wheel spin a little. But I'll try the slippery hill test you suggest to confirm that. Then I'll get it up off the ground and see if I can see a port for checking hydraulic pressure and I'll change the ATF while I'm at it.

I'm still not clear on whether the inside rear wheel skipping indicates a rear diff problem, or would that also tend to happen if the rear diff was OK, but AWD engaged and I had a bit of torque bind (e.g. malfunctioning clutch or transfer valve). Just trying to confirm that I am not actually chasing two problems.

Thanks again for the help, I will roport further on what I discover.
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post #4 of 5 (permalink) Old 11-12-2012, 07:34 PM Thread Starter
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Update

I have done a thorough test on a steep hill of loose gravel (with observer). There is no doubt that the rear wheels are still driving with the FWD fuse in. I have replaced the ATF and added seafoam - I will drive it a few days and change again. Checked the rear diff oil too - level is good and oil looks and smells OK.

Assuming the ATF flushing does not cure this, I guess this means an expensive trip to a transmission shop or Subaru dealer... unless anyone has any other ideas? I could not see an obvious port for checking pressure on the transfer clutch - anyone know where it is on a '98?
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post #5 of 5 (permalink) Old 11-12-2012, 08:13 PM
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Quote:
I could not see an obvious port for checking pressure on the transfer clutch - anyone know where it is on a '98?
See attached which I believe is 99, but should be similar (test plug is on the extension case). Test pressures might be different but, again, there should be similar changes if all is well. In particular, if significant pressure is apparent with the FWD fuse in place, then the solenoid/transfer valve isn't working properly.

Try the multiple ATF changes with some engine running in between -- this sometimes works to free things. If not, the tail section has to be removed to access the solenoid and the clutch pack. 4eat tail section rebuild without removing transmission will give you some idea of what's in there.
Attached Files
File Type: pdf MSA5TCD99L192.pdf (17.8 KB, 47 views)
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