Roller Bearing Adapter

A roller bearing adapter is the part of a truck that sits between a wheelset roller bearing and the sideframe pedestal. It is the load path through which each corner of the truck rides on its bearing.

Where It Sits

Each wheelset carries a roller bearing at each end. The adapter is a shaped steel saddle that rests on the curved outer surface of the bearing and fits up into the pedestal jaw of the sideframe. There are four adapters per truck, one at each pedestal. The pedestal roof above the adapter is protected by a pedestal wear liner.

What It Does

The adapter transmits the vertical load from the sideframe down onto the bearing while allowing the small relative motions a truck needs. As the truck warps to negotiate curves, the adapter is free to pivot and slide a controlled amount within the pedestal jaw, letting the sideframe move relative to the bearing without binding. It also locates the wheelset fore and aft within the truck.

Wear and Inspection

Because the adapter is a sacrificial wearing part between two expensive components, it takes wear that would otherwise damage the bearing or the sideframe. Worn, cracked, or improperly seated adapters are condemnable and replaced. Limits and conditions for the roller bearing adapter are set out in the applicable AAR field manual rule.