Subaru Repair: problem with turning wheels in awd, viscous coupling, gm dealers

Question
Just bought a 1996 legacy wagon.  Noticed the FWD light was on; found the fuse
to set it back to AWD; now when I turn into a parking space or make a sharp
turn (left or right) the front wheels thump and the engine starts to sputter; I put
the fuse back in to go back to FWD and the problem disappears;  I want to use it
in AWD.  Is this a problem with my wheels or the AWD?

Answer
Your problem is probably in the transfer case part of the transmission. First, check your tires. On a AWD Subaru, your tires must all match - same size, same tread pattern, same brand, same model, and same amount of treadwear. If everything matches, then, if you can get it on a lift, set the tire pressures to be the same and then measure the circumference of each tire. If any one tire is more than a 1/4 of an inch different than another, you need new tires. They all have to match for the AWD to work correctly.

If the tires are ok then it is probably a problem in the transfer case section of your transmission.

If you have a manual transmission, you may be in trouble. Have a Subaru expert check it, because the center differential or viscous coupling may be bad. I am not sure how serviceable that is. We have only seen this problem a few times on a manual, and it was fixed by replacing the entire transmission with a used unit.

If you have an automatic transmission, you still may be in trouble, but there is one cheap fix you can try. Drain the transmission fluid - which is real easy on a Subaru. Find the drain plug for the transmission, remove it, drain the fluid, install a new drain plug gasket before putting the new gasket in, and then refill with new fluid - about 4.5 quarts. After filling the trans, add GM limited slip additive, available from most GM dealers. It is a 4 oz bottle and it is great stuff. Drive around in circles and figure 8's, both directions, for about 5 minutes. Most of the time, if the problem is in the transfer case part of the trans, this fixes it. If it doesn't, you probably need transfer case clutches, valve body, and maybe even a housing - $1000 - 1500 around here.

Good luck!