What causes 1989 Jeep Laredo front end to shimmy?

Answer 1

alignment, worn tires, bad suspension parts...can contribute.

I tried 1) shocks, 2) tires. Other parts were OK'd by one mechanic, but others were ready to replace anything. I find that when tires are allowed to go out of balance, the shaking returns slowly (with gradual imbalance) but goes away immediately with rebalance. The new shocks seemed to help with control if vibration started.

What you're encountering is called a death-wobble and there's three common causes: 1) Unibody Cherokees wont accept anything larger than 32" tires without consequences, the weight of the tire/wheel combo causes the tires to fight against each other and wobble at highway speeds - when it happens all you can do is to pull over and slow down until it's back under control.

2) Wheel imbalance will often cause heavy enough vibration to start the death-wobble and the larger the wheels are or the more hard impacts they take while driving can cause weights to fly off and the wheels become imbalanced.

3) The front suspensions tracking bar has a ball-socket similar to a tierod end that will wear out and become very loose, when this happens you lose stability between the left and right tire allowing excessive wiggle and again you're back doing the death-wobble. Replacement tracking bars generally have grease fittings and lifetime warrantys which is a HUGE improvement over the OEM part, some also come with a removable/replaceable end that's also very nice.