Chevy Luv Junkyard Jewel, Part 5: Four-Link
The Missing Links
For those of you following along with our little Junkyard Jewel Chevy LUV project, you may recall that we have two link bars left over from a TCI triangulated four-link kit, so we're left with two more bars to build—the lowers, in our case. We'll be sticking with a triangulated four-link, and we've chosen to build the lower bars out of 2x2 square tubing as we plan on doing a 'bag over bar set up.
Now, there are entire books written on four-links alone, so we're not going to get into the science of the whole thing, but four-link setups have been used to plant huge power to the ground, help compensate pinion angle changes through suspension travel, and allow for great articulation (twisting—think rock crawlers) of the suspension. The common varieties are the parallel and triangulated four-links, with the parallel having two equal length bars on each side above one another in-line with the framerails, requiring some type of means to control the side to side movement of the axle. A Panhard bar is commonly used to deal with this, however, because the bar is mounted to a framerail on one end, and the axle on the other, as the differential moves up and down, the arc of the bar causes the axle to sweep slightly side-to-side, the longer the Panhard, the less the movement, but there will always be some. For you guys tuckin' big rollers, this slight side-to-side movement could wreak havoc on your fenders and wheels. A more recent trend to deal with this is a Watt's link, which is slightly more complex, and has two opposing link bars, anchored each on one of the frame rails, and on the other to a link with a center pivot that is bracketed to the rear axle housing. The opposing arcs of the two bars, along with the center pivot link work together to keep the axle centered, and look pretty trick doing it, but adds a fair bit more complexity to your four-link setup. Google it—you'll get the idea. The long-time favorite in the minitruck world has been the triangulated four-link, by moving the rear of the upper link bars inward at an angle to the center of the differential housing, the angle of the bars effectively takes care of the side-to-side movement of the axle. And by playing with the lengths of the link bars, they can be set up to handle the pinion angle changes the same way as the parallel four-link.
For our lower four-link bars, we made a stop by Zeebs Performance Restoration to get an idea of exactly what it takes to scratch build a nice set of bars. Working off the length of our upper link bars (29 inches), the width of our framerails (36 inches), and considering the angle of the upper bars, we mocked up our setup on a bench top and ended up with a lower bar length of 26 inches. Why the difference in length? Because the upper bars are running at an angle to the frame rail, the effective length of the bars from point A to point B becomes that of a shorter bar, and by building the lower bars that same length, the arcs of the upper and lower bars becomes the same, which in turn maintains pinion angle change as the suspension goes up and down. If all four of the bars were the same length, as the upper bars are angled, their effective length would now be that of a shorter bar, resulting in the upper and lower bars each having their own arc, different than the other, causing the pinion angle to pitch up and down more than desired. Anyone who has had some bad driveline vibrations at different ride heights likely has first hand experience of this.
Now the reality is, most of us don't have the equipment to scratch build the pieces to build our own link bars, nor the money to have a reputable shop spend the hours required as outlined in this article (time spent, by the way, was in the neighborhood of six hours). Sure you could use a chop saw instead of a lathe, and a grinder instead of a band saw, but quality of the finished product and time spent will still be an issue. There are options, however—anything from complete built-to-your-specs four-link kits, to all the bits and pieces you need to weld up your own link bars. Zeebs sells Welders Series parts that would have given us all the parts we would have needed, with assembly/welding being the only task left for us. Consider the various aspects of cost; the time spent, cost of parts, and quality of the finished product, sometimes building it yourself isn't always the best option, take the time to do your research.