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I have a 2 inch fiberglass crack just behind the sill plate (pass side) on my 78. What would cause that. Frame is solid , no rust. Hope it's just too much torque from the 454
Never heard of an engine doing that, but maybe a ball hit it? Even that wouldn't be enough. I say something hit it. I'd stick a strand or two of fiberglass underneath it and go from there.
when you say sill plate i think of the lower door jamb, if this is where
you mean is it possible that someone slammed the seat belt buckle
in the door?
i know with my 78 i have to be really careful because
the passengers side does not retract sometimes and i almost
caught myself slamming the door on it.
Typically,the C3's get stress cracks in the radius corner openings at hood...If you race in autocross like I did years ago with stiffer suspension,only cracks I got were in the lower spring pockets at crossmember and once broke my drivers seat slide in half...