i own a 65 electra and at 45mph it starts to vibrate. When i throw it in neurtral it still is there. Had every thing checked brakes tires balanced etc. Could it be the drive shaft or u joints. It starts at 45 and stops at around 55 or 60 and is smooth from then on. Any ideas ??
driveshaft could be worn out (some are actually two pieces, and have a rubber insulator between the two, that rots out after a few decades), or it could simply have something stuck on it and is getting thrown out of balance. Could have lost a balance weight from a wheel might have a wheel that's warped or dented could have a bad tranny mount could have a broken motor mount might need new front end bushings might just need an alignment u joints might be bad, but they usually making a clunking noise at shifts or under hard acceleration
If you have changed transmission and or engine, the pinion angle may be different or out of alignment. just my opinion... goo
had a truck once with same problem, sold truck to a GM mechanic who later discovered the harmoic balancer was wrong for year of motor , just a thought
