The wheels came off

What does "when the wheels came off" mean, and from where did it originate?

It means the wheels came off and the vehicle, etc., has come to a full stop. Reminds me of:

"You've Been A Good Old Wagon But You've Done Broke Down" -- Ben Harney (1871-1938). www.loc.gov/folklife/Gordon/sideBbandB4.html