My -76 Cadillac Eldorado is vibrating when I am driving. Anybody who knows what this may be?

Could be a lot of things what speed does it do it at.

Around 50-60 miles per hour the Car is vibrating. This car is a convertible.

Sounds like its probably an unbalanced tire. An unbalanced tire causes a vibration anywhere from 45mph to as fast as the car will go. There is no specific speed where it starts and stops other than 45+. Take it to a shop look for a coupon usually runs about $30 USD for a rotation and balance.

The tires is only two years old. The mark is American Classic, white side. They were balanced before I put them om the car.

Do you get the tires balanced and rotated every other oil change?

Nope, do you mean there is a combination? What have oil change and tires in common?

Oil change every 3000 tires rotated and balanced every 6000. I'd say %95 of the world doesn't know that the shock absorbers should be replaced every 50000. People tend to rely on their mechanic to tell them what needs done. After driving a vehicle for so long you don't even notice noises that occur and the general wear put on a vehicle seem completely normal.

ok

To understand you right, tires rotated means per mile? I'm from Norway, please excuse my bad english.

English is good, only thing that gave away you being foreign is your name, and yes its in miles. I'm curious what are your oil change intervals 5000 Kilometers? If you really want your car running its best hop on the web and search for maintenance intervals.

Thank you for the answers. It was helpful.

Did you get it checked?

Not yet. I had to change a tire because there were a crack. Look like somebody had fun with a knife. I change the oil one time a year. I drive only summertime with my Cadillac. Store the car in a garage wintertime. We repair wintertime and drive summertime.