Are you sure the 4wd is the problem? Based on your description, it sounds like ball joints, or a u-joints.
As far as running it without the front driveshaft, I don't think it wil work. The A4wd has a speed sensor both for the front axle and the rear. If the rear spins, the sensors will identify that and engage the front. However, with the front disconnected, I can't say for sure what will happen.
Monday, February 22nd, 2010 AT 11:24 AM