So there i was cruising in my dart like i always do......it's a daily driven car.
68 dart with the original slant six, a 1976 cast iron OD 833 and the original 7 1/4 rear end.
I am cruising down the highway imagining that i am drafting Richard Petty and suddenly at 80mph i hear a very loud "BBBRRRRRRRRRRRRR" i slow down because it skeeered the crap out of me and the sound and vibration shook the whole car. As soon as i slowed down to 75 it went away and everything was smooth again.
So i get a little brave and push it back up, and when i hit 80 "BBBRRRRRRRRRR" again.
No idea what it is, i stopped and checked .....trans and rear fluid check out, only happens at 80 or above.
Freaky
Any idea what it is???