66 dart 225 auto starter ?

You could have a mismatch of starter and ring gear. It would depend on the year of your transmission (automatic I presume) and the year and type of starter. If it's a '64 or later transmission (converter) and '64 and later starter, they should work together. '60-some '63's could have the earlier stuff which don't play with the later parts.....can't mix and match.