Measuring For a Spring

There are two different methods you can use to determine which spring length you need:

Method A: If you are using an axle with vertical perch bolt holes, you simply measure center to center of the spring perch bosses (taken from the top side of the axle) and deduct 5 inches. This will be the length you need for a spring-over application.

Method B: If you already have your axle, perches, and shackles, you can assemble them and situate the shackles so that they are horizontal. You can then measure from the centerline of one shackle pin to the opposite one as shown in the diagram. This will give you the length of the spring you need.

Note: If you have chosen the correct spring, your shackles will be at a 40°- 45° angle when the spring is under a load with full vehicle weight on it.