I agree that removing the trans mount does nothing to help figure out what is causing the vibration in the first place. My objective of the test was to try and figure out how the vibration that was produced in the engine/transmission was being transmitted through the seats and steering column/wheel. Since replacing the motor mounts did not help at all and I did not have another trans mount I thought that removing it would isolate the rear of the transmission from the body. I don't believe that there is anything wrong with the transmission mount that I have. There is no contact anywhere between the mount and the crossmember or body. Since the vibration occurs while running the engine in Park, driveline geometry does not come into play. I removed the mount on a 2 post lift, left the crossmember in place and removed the through bolt and two bolts into the transmission without lowering or raising the end of the transmission appreciably. I then started and ran the engine only in Park. I don't think any transmission mount will be able to dampen the vibration that is coming from the engine/trans so I am going to focus on finding the source of the vibration.

I have used a vacuum gauge a lot during this search. Yesterday I went back through the ignition system. The distributor is an original points unit that I refurbished. It does not have the electronic vacuum advance on it, it has a conventional vacuum advance can. Timing at 750 RPM idle with VA disconnected is 15 BTDC, vacuum is 16" and steady. Vacuum was measured off port on rear of carb. VA is hooked to a ported signal from the front of the carb. Carb is an original Holley 4368. Timing all in at 2850 RPM is 35 w/o vacuum advance.

With the engine idling I took a RPM reading from my timing light and then removed the wire for a cylinder at the distributor cap and recorded a second RPM reading. I repeated this for each cylinder and at an initial ( all wires in place idling normally) RPM of around 1040 and a second test at a RPM of around 740. For the 1040 RPM test the RPM drop varied from a high of 115 RPM to a low of 55 RPM. For the 740 RPM test the high was 50 RPM and the low was 30 RPM. With a plug wire disconnected the RPM's jumped around a lot, so I had to try to make an estimate of the average RPM from watching the numbers on my timing light. This obviously introduces some errors in the data. Other than confirming that each cylinder is firing I'm still trying to figure out what the data is telling me.

I also used a IR temperature gun to measure the exhaust temperatures as near to the outlet of each cylinder as possible. They varied from 640F to 540F on all cylinders but #1. It measured 470F to 490F on multiple tests. Again, not sure what the low temperature on one cylinder is telling me. Temperature variation could be just leaner or richer mixture at each cylinder since I'm relying on a carb.

I've been working on cars and engines as a hobby and made my living as an engineer working in and around lots of industrial machinery for more than 50 years. I've never run into a problem like this that seems to have no answer. I'm sure the answer is there and I will find it eventually, but it is at this point trying my patience. Thanks again to everyone that has helped me try to figure this out.

Regards,

John