It depends on why you have no AWD. In my case, the transfer clutch basket was broken. (See photo.) These parts are grinding around inside your tranny. I don't know how long it'll take to cause problems, but I'm sure it's just a matter of time. (I drove around for five days before I fixed it.)
If it's just a slipping clutch, malfunctioning solenoid, or frozen valve; it's completely harmless. If it's not, you're taking chances. You can test the solenoid fairly easily in two different ways:
First, check for
trouble codes. You're looking for trouble code 24, "Duty Solenoid C." You may also have a latent [stored/previous] code 32, "Vehicle Speed Sensor 1," from spinning your front wheels.
Second, open the hood and turn on the ignition, but don't start the car. Listen underneath the car for a quiet clicking/buzzing noise. Under the hood, open the fuse box and put a fuse in the FWD fuse slot. The clicking should go away when you do this. If you notice a difference in the noise, the solenoid is working.
If it's a broken clutch basket, you can pull out the
sensor (Vehicle Speed Sensor #2 I think?) from the tranny. The dark oily hole in the top center of this
photo is where the sensor is located. You'll need a 10mm wrench to remove it. (It'll help if you have a jack or some ramps to get under the car.) When you pull it out, if there are a lot of
metal shavings on it, you're clutch basket is almost certainly broken.
If the clutch basket is broken, it only grinds when you turn sharp corners or spin the front wheels. If it's already broken, it's probably made a big mess of metal shavings, but it'll take longer to make a bigger mess if you don't spin the tires.
Frankly, I don't know what the long-term consequences are if you drive around with a broken basket. I recommend you replace the basket as soon as possible. If it's a plugged fluid passage, it may cause things to wear out quickly. If you can turn a wrench, you can change a broken clutch basket yourself. You don't have to pull the transmission - just the housing at the end of it. I'm not sure where to get a replacement. I welded mine back together, but I'm not willing to recommend that because I've only been testing my repair for a few days now and I don't know if it'll last. (I think it will - it has so far.)
Tranny photos in my locker:
http://www.subaru-svx.net/photos/user.php?UberRoo|15418
