The Making of a Good Leaf Spring Suspension
To get the proper replacement springs requires correct measurements—the wrong way to do it
Achieving a smooth, nice riding and handling leaf spring suspended vehicle is very simple, provided some basic rules are followed.
1) Multi-leaf springs: Only with multi-leaf springs can the correct spring design be achieved. Springs support weight, absorb road shock and set vehicle height. With multi-leaf springs, critical design factors such as stepping, rate, load, and spring height can be fine-tuned.
2) End type: Square ends, or constant thickness ends are great for trucks, while diamond pointed or trimmed ends will improve ride quality.
However, for the smoothest riding spring, the ends must be tapered.
Tapered leaf ends move the friction area away from the leaf ends and spread it over a much larger area, resulting in less force needed to flex the spring.
3) Blocks: The use of blocks to either lower or raise a vehicle is the leading cause of axle windup and poor vehicle handling. The most secure suspension is one where an imaginary line drawn between the spring eyes is as close to the axle seat as possible. The use of blocks takes this line away from the axle seat resulting in a fulcrum point. This leverage point allows the axle to pivot around the spring seat causing axle windup and handling problems.
Springs will deform for a variety of reasons, including removing leafs like we did.
4) Shackle angle: As a spring flexes, it grows in length. The purpose of a shackle is to allow for this growth. Although spring rates are fixed by its makeup, the amount of force required to move a spring can be greatly increased by incorrect shackle angle. Any shackle angle exceeding 15 degrees is too great.
What’s Next for the Hot Rod Hauler?
Originally, we dropped the rear of the Hot Rod Hauler 3 inches by modifying the stock springs, and that left us just enough room between the axle housing and the framerails for suspension travel. We’ve since installed a proper pair of de-arched springs to lower the truck the same 3 inches as the modified stock springs, plus we’re relocating the spring hangers to drop it another 3 inches. Of course, now we have to modify the framerails for axle clearance—but that’s yet another story. CCT