Constant Contact Side Bearing (CCSB)

A constant contact side bearing, or CCSB, is a type of truck side bearing that maintains continuous spring pressure between the truck bolster and the car body. Unlike older clearance-type side bearings that only touch when the car rocks, a CCSB stays in contact at all times.

Where It Sits

Side bearings are located on the top of the truck bolster, outboard of the center bowl, one on each side. The CCSB mounts on the bolster and bears upward against the mating body side bearing wear plate fixed to the underframe of the car body. The car pivots on the center bowl, while the two side bearings steady it at the outer edges.

What It Does

By preloading a spring or resilient element so it is always pressed against the body, the CCSB applies a controlled friction and roll restraint between truck and body. This frictional resistance damps truck warp and resists the high-speed weaving known as hunting, which improves ride stability and reduces wheel and rail wear. It also helps control body roll without preventing the truck from turning under the car on curves.

Wear and Inspection

A CCSB has a working travel range and a defined setup height; modern long-travel designs allow a limited amount of travel before the unit goes solid. Worn-out springs, units that have gone solid, or incorrect setup heights are correctable conditions. Side bearing setup and condemnable limits come from the AAR interchange rules and field manual.