Q. A couple of months ago you wrote an article on rear suspensions, which included truck arms. I would like to have a little more information about them.
Where would the projected intersection point of the arms be located on the chassis? Are the arms a standard length or does the length vary per application?
Via the Internet
A. Truck arms work the same as the popular ladder bars that many street rods use, the main difference is the material they’re made from. Truck arms as made by GM are fabricated I-beams—they were used on ’60-72 Chevrolet and GMC pickup trucks and a similar version made from U-shaped sheetmetal could be found under early Oldsmobiles. Chevy and GMC trucks used one big U-bolt on each side to secure the rearend housing to the arms, Olds used a bracket assembly and rubber mounts to fasten the components together. Ladder bars normally attach to brackets welded to the rearend housing with adjustable clevises to allow for pinion angle adjustments (something Olds/Chevy/GMC didn’t have to be concerned about). At the chassis the truck arms and ladder bars attach to a crossmember near the transmission’s U-joint, the pivot points are as close to the centerline of the chassis as practical to reduce binding when the vehicle leans in a corner.
While not particularly sophisticated as suspensions go, truck arms and ladder bars work quite well. They eliminate wheel hop under acceleration and braking. They are simple with just a pair of bushing as wear points, easy to install, and very affordable.
Stock Chevy and GMC truck arms where two pieces of material joined to make an I-beam. Coil
Several suppliers offer replacement arms fabricated from tubing for Chevy and GMC trucks.