Dave, Mine is a ‘48 3100 but with a 327/700R4/3.73 Posi/255-70-15’s on Progressive aluminum rims-also front disc brakes, and I’ve also kept the original solid front axle. The sweet spot at highway speeds is about 72mph, although I’ve had it up to 85mph (at which speed my common sense kicks in?). No vibration. I doubt your vibration can be attributed to the solid axle. Many years ago at the shop I started at the manager required that if a tire had a dot on the sidewall (orange, yellow, red) that it be lined up with the valve stem hole on the wheel. The explanation being that the tire and wheel companies marked their product accordingly such that the alignment of the dot and valve stem would insure that the high spot of wheel was matched to the low spot of the tire thereby keeping the radial runout of the assembly to a minimum. Common sense. Not to long ago I got a new set of tires at Firestone and my “sweet spot” was GONE! Bad vibration at 55-65. Back to Firestone and a rebalance improved the situation marginally. I got my dial indicator out and the left-front had .090” radial runout!!!! After close inspection I could see the orange dot on the sidewall on 3 of 4 tires and they were NOT aligned with the valve stem. Back to Firestone and I had them remount the tires: problem solved! Dave, above you said you dial indicated “everything”. Have you checked your lateral and radial runout on your wheel/tire assemblies? This will also confirm if you have any flat spots on your tires from sitting. Specs attached…. Good luck, Dave
