5398-17121
Rear Cap HBDMTR 8.25 x 54M
Mack

The rear cap is a protective seal and enclosure piece designed to fit hub or bearing assemblies on heavy‑duty axles. This cap helps keep dirt, moisture, and debris out of the bearing area while retaining lubricant in the race path, thereby extending bearing life and reducing maintenance intervals. The 8.25 inch sizing and 54M designation indicate tight tolerances required for proper alignment and sealing in the hub assembly. By preserving clean operating conditions, the cap minimizes contamination‑induced wear and helps maintain consistent bearing preload and smooth rotation. It also contributes to quieter operation by limiting grit intrusion into critical contact surfaces. When replacing this part, verify proper seating and seal orientation to ensure an effective barrier against external contaminants. Regular inspection of the cap and surrounding seals complements routine hub service. For fitment confirmation and installation specifics, consult Source One Parts Center.