Brazilian Dodge Dart 76 (similar to 69 usa)
it looks like you have the tube sticking out of the vise way to far,,,,look at the instruction book,,i think you are using the wrong adapter to measure the height of the tube sticking out,,,
sticking out to far is making it to hard to compress it to the proper size causing the bad end and cracking
slso make sure you cut the end square and debur the inside of the tube before clamping it in that clamp