vibration in a 1972 plymouth roadrunner?

does it change with engine RPM if so my guess would be the tourqe converter is imbalanced.

I was already a teenager when Hot Wheels came out (late 60's), so at that time I was fascinated by Mad Magazine, Hot Rod Magazine, music and good drugs! But every Friday night you'll still see me cruisin' for burgers in my red 1957 'Corgi' Chevy Bel Air...The chicks love it! Then when I run out of gas, I come home and build the Eiffel Tower with my Meccano! I still have my 50 year old set, complete with motorized crane! When I'm feeling really nostalgic I'll dig out my Lincoln Log's, or my 'Tinker Toys'! Man I wish I was a kid again! Thanks, now it's time for an adult beer! Edit - I'm curious what kind of a** would give thumbs down to these answers...that's just plain stupid! I betcha that same moron will give me one as well. Makes me wonder about people for sure. They need to play a game of G'nip G'nop, or Toss Across, and loosen up a little!

I have owned several roadrunners and only encountered the problem you discribe once. It was in a 1972 340 4 speed I had in 1985. Isearched out all the normal items (clutch, balancer,etc.), it turned out to be a slightly bent fan blade that was barely noticable until removed to look at.

I would start with checking the motor mounts first see if they are in good shape. Next I would check the harmonic balancer to see if it slipping apart. Take a look at your flex plate and see if possibly it is bent, cracked or had a balancing weight come off. The last thing would be if the engine itself is out of balance. If the motor has been blueprinted it may have been internally balanced. If you have had to replace the flex plate or harmonic balancer you can totally throw the motor out of balance. Also if it has been balanced you may have had a slug of heavy metal fall out of the crank. When they balance a crankshaft if the rod/piston combo is heavy they have to add weight to the cranck throw to counter balance them. Hopefully it is something simple but if you suspect the engine have it looked at ASAP an out of balance engine will start to take out bearings and such very quickly.

Could be a lot of things. If its the engine thats vibrating it could be the plugs are fouled, or one (or more) of the cables are cracked. Another likely cause might be a vacuum hose is off or cracked and leaking.

There are MANY things that could cause vibration. These are just some ideas where to start.

Glen is right on with his answer about the mounts

check the front engine pulley. it has a rubber insert that allows it to cancel engine vibrations. the rubber may be shot. do not run the car with a bad balancer since it can damage the engine. other things to check - loose flywheel/ clutch, bad throwout bearing, bad bushing between the rear of the crank and the tranny, broken motor mount, bent belt pulley on the alt, water pump, or AC compresser, loose mounts for alt,AC compresser etc,

Is it automatic?, If it is it could possibly be the torque converter out of balance,coming apart inside..I have had it happen to me on an old plymouth.

Take it to get check by a mechanic!!

You can't live with that1 I'll give you $1000.00 for it, okay?

nothing that is what it is suppose to sound like