It seems vendors like to say that for drops more than 4" that a long track bars should be used. Lets take a look. Stock Length Track Arm I modeled the rear suspension using Autodesk Inventor to see the articulation of the rear axle as constrained by the stock track bar and trailing arms. Truck is a '65 C10 with 5" drop springs. Image below is an aerial view with frame at ride height: I turned off the visibility of the gas tank so the rear axle / track bar could be seen more clearly. Image below is the frame is at ride height (rear cross members removed to allow viewing of track bar) Note angle of track bar in the following photos Image below is fully bottomed out; frame is on the top of the rear axle tubes. (NOTE: This moves the axle to the left approx. 11/16" from the std. ride height position) Image below is fully articulated, hanging on left side, bottomed out on right side. (Note: This moves the axle to the right a negligible amount < 1/16") Image below is fully articulated, hanging on right side, bottomed out on left side. (Note: This moves the axle to the left approx. 1/2" from the std. ride height position) Now lets look at a popular bolt on "Long Track Arm" Image below is the frame is at ride height. Image below is fully bottomed out; frame is on the top of the rear axle tubes. (NOTE: This moves the axle to the right approx. 1/2" from the std. ride height position) Image below is fully articulated, at hanging on left side, bottomed out on right side. (Note: This moves the axle to the right a negligible amount about 1/8") Image below is fully articulated, hanging on right side, bottomed out on left side. (Note: This moves the axle to the right approx. 1/4" from the std. ride height position) Summary The longer bar helps, but not significantly. I am betting that’s why GM never used them on these trucks. I haven't been a big fan of these long bars simply because they aren't really needed on a street driven truck. Think about it. A stock 3/4 ton truck with stink-bug high rear end height, now fully load it down. Your street driven truck will never see more suspension travel than that, right? Now if your running a rock crawling 4x4 with a lot of suspension travel like my buddy Tony's Bronco in the photo below, the long track arm will make a whole lot of sense.... lots of articulation here: Hope this helps! John
I always understood the reasoning behind the longer track arm in extreme lowered applications is mostly for clearance/obstruction purposes...locating the rear housing mount lower. Great modeling and explanation!
John, Great visuals, really illustrates the point. Question- I have seen panhard rods/track bars that are welded directly center of the differential, i.e.. a very short bar. Wonder how this would affect the location of the axel in comparison to your other illustrations. Haasman
The shorter the bar even for street applications would result in a quicker off center axle alignment, I would go with a longer bar or factory lenght if at all possible, those running bags really need to run a watts link as shown here for the amount of travel their suspension see`s. When I lowered my truck I used an adjustable bar, at normal ride height it resides perfectly horizontal from frame to axle.
