Typical 4wd Steering Setups
Crossover: Drag Link To Knuckle
A drag-link-to-knuckle type crossover steering is probably the most common aftermarket steering system setups. It's also one of the most ideal designs. The drag link drops from the pitman arm directly to the passenger-side knuckle, preventing any type of radial drag link and tie rod play due to ball joint movement. From the passenger knuckle, the tie rod provides steering control and movement to the driver-side knuckle.
Crossover: Drag Link To Tie Rod
This type of crossover steering is probably the most common factory-produced system. With this setup, the drag link angles down from the pitman arm and connects to the tie rod. The tie rod not only keeps the knuckles parallel, but also controls movement of both knuckles. The design inherently has a minor bit of play, even when brand new. Since tie rod ends are spherical and rotate for knuckle motion, the tie rod is thus allowed to twist a few degrees. With the drag link connected to the tie rod, the drag link will be pulled away from the pitman arm or pushed toward it as the tie rod rotates causing a minor bit of wandering.
For various reasons, sometimes to eliminate feedback to the steering wheel, stress on the steering box, or to get around a protruding framerail or Panhard rod, double crossover steering is utilized with a bellcrank and a tie rod in between the bellcrank and the pitman arm. From the bellcrank the drag link drops to the tie rod or knuckle, but on the driver side while the bellcrank sits on the passenger-side framerail.
A common OEM solid-axle steering setup consists of a Y-link design where the tie rod ties into the drag link instead of providing a solid link between the two knuckles. Here the drag link drops from the pitman arm to the passenger-side knuckle, and the tie rod picks up straight off the drag link and follows to the driver-side knuckle. This system has one negative aspect: as the drag link and tie rod "flatten out" during suspension compression, the tires will point (or toe) out. As the suspension droops, the tires are toed in. With a stock suspension, the limited amount of travel makes this change in toe negligible.
(IFS) Recirculating Ball And Tie Rod
In an independent front-end setup that uses a steering box, the steering has a centerlink in between the steering box's pitman arm and an idler arm. Two tie rods drop from the centerlink to the knuckles, and control knuckle movement. This is an OEM design that is still utilized today in vehicle manufacturing because of its strength advantages over the newer and more advanced system of a rack-and-pinion.
Rack-and-pinion steering is a more modern independent-suspension steering design and is slowly making its way into independent-suspension 4x4s. The rack-and-pinion setup has a pinion joined to the steering shaft and its gears meet up to a rack, or geared track that moves from side to side as the steering wheel is turned. Two tie rods leave the rack and end at the steering knuckles, controlling wheel movement.