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Old 03-13-2011, 07:36 PM   #1 (permalink)
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Default AWD not working

Hey all, brand new to the forum and a new outback owner. Have a 96 outback and the all wheel drive is not working. Its a 2.5 auto, there is no fuse in the fwd slot and also there is no awd light that displays during startup. The olny diagnosis I have done so far is to jack all 4 tires up and put it in gear. The rear drivline is dead, nothing turns. I have read and searched with no luck and could use some help. I am a seasond toyota mechanic with no idea on how this system works. I ran across a few mentions about the vc but nothing detailed. thanks
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Old 03-13-2011, 09:42 PM   #2 (permalink)
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Is there a propeller shaft going from the back of the transmission to the (a) rear differential? (Subaru, around that time, made both FWD and AWD versions and some have been caught by this.)

Automatic or manual? The manual will not have an AWD light. The automatic will, and when the key is turned to On, but the engine not started, it should come on, at least for a short time. If it does not, the bulb is probably burned out. (There is also an AT Oil Temp light that is important for the OBD. It too should come on when the key is at On, and it should not flash -- this would indicate a detected problem.

The manual transmission with AWD uses a center differential with a viscous coupling. Most common problem is the VC seizes and the car is in full time full 4WD. The automatic with AWD uses a multi-plate transfer clutch controlled by the transmission control module. It sometimes fails in the fully on mode, but in your case it could be that the clutch isn't engaged, either due to a control problem or badly worn out clutch plates.
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Old 03-13-2011, 10:04 PM   #3 (permalink)
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The trans temp light comes on and goes out ofter a second or two with no flashing. and it does have a propeler shaft, rear diff, and all the other stuff to make it an awd, I did check Finally found a thread on the subject and it addressed some of the possible causes. The clutch solinoid is ruled out, so now im leaning toward a worn out clutch pack or a speed sensor ( would a fualty sensor throw a code) The car has 197000 on it and the trans was just service. And thanks for the quick response!
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Old 03-14-2011, 07:13 AM   #4 (permalink)
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Quote:
The clutch solinoid is ruled out, so now im leaning toward a worn out clutch pack or a speed sensor ( would a fualty sensor throw a code)
Yes, a faulty VSS should trigger a code (32 or 33).

For the most part, the solenoid could be ruled out because it's normal failure mode is "off", which will apply full pressure to the clutch piston; i.e. full clutch and full time rear drive. But the solenoid is only one part of the control -- there's also a transfer valve which could (although rare) be seized in its closed position. (See attached)

To really know, the best test would be to monitor the clutch hydraulic pressure. There's a port for this on the side of the extension case. This will quickly confirm if hydraulic pressure is being applied to engage the clutch, and if it is, then it's likely the clutch pack is gone.

There have been instances where the clutch drive plate housing has separated from the reduction gear, and I recall one case where the output shaft had broken. In either case the pressure measurements would have indicated the correct levels. Nevertheless, the outcome is the same -- the extension case has to come down, at which time whatever the problem is will be revealed and can be readily repaired. The idea, however, is to be reasonably sure it's something in the case, and not elsewhere, before going that route.
Attached Files
File Type: pdf Transfer system early.pdf (122.2 KB, 252 views)
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Old 03-14-2011, 08:27 AM   #5 (permalink)
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Plain OM thank you so much for the info, may let the dealership test the pressure and the electrical signal before I crack the case to have a look.
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Old 03-21-2011, 10:17 AM   #6 (permalink)
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Ok, delership is a little unreasonable on the cost of diagnosis, so I will stop by the industrial supply and pick up a gauge to measure the hydrolic pressure. The parts stores in this area dont have a anything to do this, big suprise
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