You cannot drive a car with a bad U joint for more than a few hours. Without the joints, the car driveshaft will not rotate freely. The level of damage on the joint will determine how long you can drive the car, but it cannot be for more than a few miles. A lousy car joint can induce transmission fluid leak, another damning factor while driving. If your car has a transmission leak, not only will it quench after about 200 miles, it might cause severe damage to the transmission system.