I have a '37 Chevrolet pickup with a 250 inch engine, Turbo 350 trans, 3.42 gear. I drove it this way four three years. Last year I replaced the 3.42 with a 3.08 and then over the winter I installed a rebuilt balancer due to mine having pulley wobble. All this summer I have been fighting a vibration at 65 mph. It comes from the Lokar shifter mounted directly on the tail shaft of the transmission. The rest of the truck doesn't shake or vibrate. It could have been there the whole four years, but I never new it with the 3.42 gear and the rpm difference.

I have rebalanced all the tires, double checked the driveline angles, checked converter for missing weights, check flywheel (new), replaced the fan, fuel pump, fuel filters, ignition modual (HEI), plug wires, plugs, two intakes, five different carburators, two different exhaust manifolds, and fuel grades.

I now believe its internal, or the new balancer. I don't recall having the problem last year. This spring, I assumed it was carburator icing up, but when it did it again in July (100 degree day) I new I had a problem. This is a show truck so I only drive it 1000 miles or less a year. I can drive through it, sometimes, say get up 70, then next time I would have to drop down to 60 or even 50 to get it to smooth out. At idle in park, the engine is dead smooth, at 2400 to 2500 it shakes, which is at 63 to 66 mph. From a dead stop, it will run right up to 4000 rpm in gear with out a vibration till you let off and coast down to the speed limit. While coasting down, I notice the vibration in the shifter. If I throw it in neutral, it goes away right away.

I guess what I am asking is, can a worn cam gear cause any problems at higher speeds? Can a balancer cause a vibration if it runs true?
What could cause a internal vibration?

I ask about the cam gears because they are the only used parts in the engine. I broke the new gear, pulling it off a different camshaft, and it was a holiday weekend and the only way to finish up was in stall a used set. This winter I plan to replace them if I pull the engine out for other repairs.

One thing I still need to do is recheck the driveshaft for balance. It was built new by a driveline shop so I don't expect it to be bad, plus it shows no sign of missing weight. The whole truck is basically new with only 4800 miles. Am I stuck at 63 mph??? Joe