1999 Jeep Shimmy

Maybe tires are worn. Have you had them rotated and balanced? Could be many things. Take it to a tire shop and have them look everything over. Wouldn't hurt to get an alignment or steering dampner.

1995 Jeep Wrangler - 137,000 miles

i am having the same problem.
The car is fine until I hit 65 mph - then it shakes violently and stops when I go below 40. :(

my mechnic has already done a balance and rotation of the tires -- and wasn't that. Any other suggestions?

Please help!

Yea I have a 1988 jeep cherokee and it does the same thing. I have changed all four u joints but it hasn't helped. I've been told that an adjustable track bar would help but i'm not sure. Any idea of this would help?

Try a heavy duty steering shock dampner, rancho make good ones, or get the original equipment replacement from a dealer, but I recommend the rancho or similar aftermarket brand, they are generaly
more heavy duty.