I'll do my best to explain this. I have an 87 Trans Am (was a carb 305) that now has a '92 Camaro carb 305 in it. When I get the RPM's around 2000, it has a vibration that travels throughout the car. It isn't horrible, but it is certainly noticeable. It occurs in gear, as well as park and neutral. I am working with a very intelligent mechanic to fix this problem. So far we have: Checked to see if there is any wiggle in the harmonic balancer (very very little), We checked the flex plate and it seems to be the correct one and in good condition. However, Bruce swears it's bolted on backwards. Does anyone know if the weight on the flex plate should face the engine or the tranny? We unbolted the torque converter clutch and it still vibrates although not as bad. Motor mounts appear to be good. We also removed the belt to eliminate the accessories and it still vibrates. The previous owner swears the flex plate and the camaro motor are matched. He also put high performance cams in as well, which leads Bruce to believe that maybe he didn't adjust the lash on the valves correctly and that is causing the vibration. Jesus, it seems like it could be anything!! If you guys have any pointers, hints, tips, advice, or heaven forbid, the solution, I'm all ears!!!! Thank you!!!!

 

I don't think the flex plate on backwards would cause this but I would be wrong. The weight should face the block. I would check all your plugs and make sure your not missing on one cylinder and just not hearing it.

 

Your flex plate might have a crack in it you don't see. The mounting pads for the converter are concaved and should face the converter.

 

Also, the damper being "loose" or having wiggle room won't tell you much if it doesn't because the weight on it could have come loose or have shifted and the damper itself be tight. Just something to look out for.

It still vibrates with the trans disconnected, so it's definitely in the "engine".