The 523-85-21 or 5238521 Fabco shift piston is the moving part that pressure pushes to operate a shift mechanism. In air-shift units it rides in its cylinder and moves when air is applied, which is what lets the unit change modes. A worn piston or seal, or a corroded bore, can let air leak past, and that tends to show up as air blowing from the case vent or a shift that is unreliable. This is a genuine Fabco part from Pro Gear and Transmission. Call us if you want help confirming it for your application.
Features
Fabco shift piston, part number 523-85-21 or 5238521
Moved by pressure to operate the shift mechanism
A worn piston or seal can leak air and make shifting unreliable
Genuine Fabco part sold by Pro Gear and Transmission
