Revealing mistake: In the beginning scene when they jump over the drawbridge there is more than a foot of space at the bottom of the rising bridge. No car, no matter how big, could have cleared that space without flipping over. Also when they land on the other side you can see a "flap" at the bottom of the bridge which would allow the car to drive over it.
Revealing mistake: During the big chase scene at the end, right before the Nazis accidentally drive off the bridge, the Bluesmobile is seen doing a backflip over their car. Watch carefully as the Bluesmobile first lifts off the ground- an air-ram is visible firing under the car, which causes the car to begin the flip. (Note: This scene has been cropped in some releases so that the air-ram isn't visible, but it is still present in other releases of the film).
Revealing mistake: When the Chicago police cars have the first major pileup underneath the elevated roadway, a number of the cop cars are seen flipping over by using two rail-like beams along the road. When the rest of the cop cars come to a stop in the next shot, the beams are gone.