Flex Joints for Suspension Movement

Articulation and Rotation for Suspension

Jay KopycinskiPhotographer, Writer

Suspension systems are comprised of components that allow parts to rotate and flex as they cycle through travel and articulation. Some type of flex joint is needed to allow this movement whether it’s on an IFS a-arm or some form of linked suspension.

Each of these joints contains some material for movement and inserts may consist of rubber, urethane, or steel spherical joints, depending on application. Vehicle manufacturers tend to use rubber joints where they can to minimize noise and vibration transmission into the vehicle. Urethane bushings are a step up in performance over rubber due to their higher material density, but often need to be kept lubricated to prevent squeaking. Some aftermarket and race suspension arms use rod ends (heim joints) at the arm hinge points, providing greater strength and durability, especially under severe use conditions. These joints transmit even greater levels of chassis noise into the cab, but don’t suffer from flex and play as bushings do.

High quality rod ends use a Teflon or similar material liner between the rod end body and the spherical ball, and are recommended for off-road use. Metal-on-metal rod ends can be lightly greased to extend their useful service life, but this is generally impractical in an off-road application due to the dirty environment. The impact loading on a suspension link causes rod end loads that will exceed the film strength of any lube used, and metal-to-metal galling will occur. Once a rod end starts to wear and loosen over time, it may not make a large difference in the vehicle behavior. However, the resulting noise created by the sloppy joint can be annoying, and may eventually lead to body failure.

Spherical uniball assemblies may be used at the spindle end of a front suspension arm instead of OEM ball joints. In the case of uniballs in suspension arms, they tend to be tighter and produce more noise than a standard ball joint. Preventive maintenance to keep the uniball assembly clean of dirt can prolong their life and prevent accelerated wear to the liner.

A number of joint types are available for suspension applications. Determining which type is best is often a question of strength, available mounting area, tolerance for transmitted noise in the cab, and the need for tight, precise suspension operation.