TOP PLATES

Top Plates For Peterbilt Trucks

The fifth wheel top plate is the wear surface that contacts and supports the trailer kingpin and underside of the trailer -- it takes the full dynamic load of a loaded trailer across every road mile. Top plates wear at the kingpin pocket and along the sliding contact areas, and a worn or cracked top plate compromises the coupling integrity and contributes to kingpin wear. We carry fifth wheel top plates and replacement hardware for Peterbilt trucks running Holland, Jost, and other common fifth wheel brands.

Frequently asked questions about top plates

How do I know when a fifth wheel top plate needs to be replaced on my Peterbilt?

Top plate replacement is indicated when the kingpin pocket shows wear beyond the manufacturer's allowable limits, when there are visible cracks in the plate surface, or when the plate has been significantly gouged or deformed from an improper coupling event. The kingpin pocket should be checked with a go/no-go gauge at regular intervals -- excessive play between the kingpin and the lock jaw due to worn pocket geometry compromises the coupling's ability to hold the trailer securely. A plate that's worn into the mounting structure below the sliding surface is beyond repair.

How often should fifth wheel top plates be lubricated on a Peterbilt?

The fifth wheel top plate should be lubricated at every PM service interval -- typically every 25,000 miles -- using a fifth wheel grease specifically formulated for the high-load sliding contact between the plate and the trailer. In operation, the plate surface is constantly sliding against the trailer underside, and inadequate lubrication causes accelerated wear of both surfaces. Many fleets use an automatic lubrication system to keep the fifth wheel plate lubricated between manual services, which is a worthwhile investment for trucks that couple and uncouple frequently.

Can I replace just the top plate, or does the whole fifth wheel need to come off?

On most fifth wheel designs, the top plate can be replaced as a separate component without removing the entire fifth wheel assembly from the truck frame. The top plate is typically secured to the fifth wheel body with bolts that are accessible with the trailer uncoupled. Replacement involves removing the mounting hardware, pulling the worn plate, and installing the new plate with the correct fastener torque. Always consult the fifth wheel manufacturer's service documentation for the specific procedure and torque values for your model.

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