Metal clanking when accelerating at 65mph, 69 roadrunner 383 4spd.

[67 Coronet Conv]

Detonation...

Yep same thing happened to me years ago, more like a pinging sound in the exhaust. Backed off the timing and all is good.

 

[Beep69]

Beep69....Did you find your issue?

No. After driving more It appears that the noise only occurs when I push hard on the gas pedal and down past 3/4 and to the floor. It even did it in 3rd gear at around 45 to 50. When I gradually push the gas pedal down even at 70 mph it didn't make the noise.

 

[SlinktRR]

No. After driving more It appears that the noise only occurs when I push hard on the gas pedal and down past 3/4 and to the floor. It even did it in 3rd gear at around 45 to 50. When I gradually push the gas pedal down even at 70 mph it didn't make the noise.

I would check the axle bearings. When they go they make a knocking sound that comes and goes with speed. Usually sounds like its coming from under passenger compartment.

 

[Nxcoupe]

Sounds like a ujoint to me.