Sometimes it has an awful shake in its ride and other times it rides smooth.

If this is accoring at the same speeds everytime start with just getting your tires rotated and balanced! It will only cost like $40. Then if keeps shaking have your tires checked to make sure they're in good condiotn. Then you go from there.

You probably need an alignment or it could have something to do with your tires. Maybe a wheel barring. Take it in and let them put it through a diagnostic test.

Could also be a broken belt in 1 of the tires. I've seen it many times, it only happens at certain speeds.

You need to have your tires graphed. Tires that are out of round can cause a car to shake.

what kind of lincoln?

if it shakes on acceleration and on gear shifts, there might be a need to flush and change the transmission fluid. Town cars, crown Vics and grand Marquis are sensitive to dirty fuid. My Crown gets done every 30-35,000 miles. Cheaper than a new transmssion

l have a lincoln also same yr only mine is a continental and im not sure what model you have. l have the same problem it feels like it bucks and my break light comes on. l wont be much help in answering, but you should bring it to a lincoln dealer just to be safe. They know more than the average mechanic lincolns are more advanced than most.

Seriously, have your tires inspected! rotated! and balanced!, this should ''smooth'' the ride out especially noticable at freeway speeds.

Wal-Mart tire-lube-express can do ALL of this for about $30.00 plus tax and it is lifetime rotation and balance.

Best wishes, make sure you get this checked.
''/JOe