Vibration when running engine at 1200-1700 rpm’s and crusing about the same.

[AcesArneson]

The guys are right, start with the balancer but before you do that just check your PCV, this would be my order of searching;
1. Check your PCV to make sure it is working fine (easiest check that could cause your symptoms). Pull the PCV out of the air cleaner and leave it attached to the hose. Start the car and let it idle. You should have vacuum through the PCV at idle. Shut the car off and take the PCV off the hose and make sure it rattles when you shake it. If it doesn't rattle then it is stuck open, replace it. Next check your PCV line hoses, a cracked or broken hose will act just like a stuck open PCV and cause fuel mixture problems which almost always result in hesitation, poor idle and rough acceleration if the hoses are 50 years old just replace them anyway, it's a miracle they haven't started leaking. A telltale sign of PCV issues is oil on your PCV line inside the air cleaner, if you have a lot of oil inside around the foam separator and the bowl of the air cleaner it's likely a bad PCV. Since your car is fine at idle but bad above idle at cruise, I would suspect it is stuck open.
2. Balancer (my money is on the balancer) TDC confirmation. It may have only moved once but if it has it will be out of balance, no amount of timing work will fix that.
3. Pull the plugs and look for evidence of fouling, bad plug, bad plug wire, fouled dizzy point. Likely time for a tune up kit anyway.
4. Doesn't sound like fuel to me but it wouldn't hurt to check the fuel filter and carb.
5. Vacuum lines, have fun!

 

[Joeaus08]

Well, I thought I would tell you guys what my issue was. We trailered the car to Cruisin' the Coast and after driving around for about 4-5 hours we experianced a blown front trans seal. After the transmission was pulled, it appeared the torque convertor bushing failed causing the trans to overheat and blow the seal. We installed new pump gears, new o-ring, gasket, front seal and bushing. While it was down, we added a Fairbanks shift kit and a deeper chrome pan that adds (2) more quarts of fluid capacity, cleaned it up and painted it as well. The bushing that came out was acored pretty good.

During the test drive, it drives great, shifts hard and like its supposed too. Best of all, no vibration! got by with about $300 worth of parts!

I know, my headers look bad, they are next!

 

[mjlan]

Glad the issue got corrected. Its always good to hear what the root cause was, especially when so many ideas were thrown out there.