Wheeler 9138133-01 MB4 Brake Master Cylinder Filler Cap

The Wheeler 9138133-01 MB4 Brake Master Cylinder Filler Cap seals and protects the hydraulic brake reservoir to prevent contamination and fluid loss. Designed for towing and push-back tractors and other airport ground support equipment, it provides secure reservoir sealing for reliable braking in industrial transport contexts. The MB4 model reference indicates an industrial-grade cap assembly that can be installed as threaded or press-fit, and it is used for brake system maintenance and replacement. Common replacements include Grove Brake Reservoir Cap, TLD Brake Master Cylinder Cap, and Tug Technologies Hydraulic Reservoir Cap, aligning with ground support, transportation, and fleet maintenance operations.