70 ft. lbs is not harmful. I have a gut feeling it's best to leave it alone.
BUT, if your determined to loosen that bolt:
Is the emergency brake "On?
Did you fit a pipe over the breaker bar to extend its length?
Are you using a long 5/8 impact socket on your breaker bar so as to avoid the use of a short extension?
Watch these videos:
https://www.bing.com/videos/rivervie...6BA7&FORM=VIRE