I had my mustang on jackstands for a couple of weeks to change out the clutchpacks for the rearend. I didnt finish because I got stuck with a broken s spring that I need to replace. we are getting a snowstorm in virginia tonight so i kept the broken s spring in, put the axles and wheels back on, took the car off jack stands, then pushed it slightly forward to the end of my driveway. I stopped the car, pushed the brakes, then put the car in gear then let off the brakes, only for the car to keep rolling. I used the handbrake and chocked the wheels instead. I tried first and second but the car kept rolling. This problem was not there before I put the car on jackstands and I havent started the engine this whole time. any suggestions? bad clutch? broken diff?