My buddy's 350 in his 39 has developed a bad vibration at about 1100 rpm. At idle and above 1100 rpm it smooths out. Seems to run great and gets ok gas mileage. We have done the following trying to fix it.
Replaced HEI distributor
Replaced spark plugs and wires
Timed it.
Checked vacuum...20 inHg
Checked booster on power brakes
Checked balancer
Checked all vacuum lines and PVC valve
Disconnected torque converter to flex plate. No joy
Checked motor mounts
Checked compression...around 170 to 180 psi on all cylinders
Looked for missing hardware on flex plate
What the heck are we missing?
Thanks.
