UP2WIN 918-04126 Spindle Assembly Fits for Cub RZT50 LT1050 Lawn Mower, Cub Troy Built Mustang Zero Turn 50" Mower Deck, Replaces 918-04125 618-04126 618-04125

What It Is

The UP2WIN 918-04126 Spindle Assembly is the rotating hub that drives the mower blades on 50-inch zero-turn mowers, specifically Cub Cadet RZT50, LT1050, and Troy-Built Mustang models with fabricated or stamped decks. It replaces the OEM spindle when bearings wear out or the housing cracks.

Fitment & Compatibility

Before buying, verify three things:

• Deck width: This fits only 50-inch decks, not 42” or 46”.
• Model series: Works on Cub Cadet RZT50 (2008–2015), LT1050, and Troy-Built Mustang 50” (2009–2016). Check your model number on the mower frame.
• OEM cross-reference: Replaces OEM part numbers 918-04125, 618-04126, and 618-04125. If your spindle has a 3-bolt pattern (bolt center-to-center ~3.5”) and a 1-inch shaft, it matches. Measure the old spindle’s bolt spacing and shaft diameter before ordering.

Key Things to Know

• Build quality: All-metal housing with sealed bearings. Most users report it’s a solid aftermarket alternative to OEM, but the bearings are not serviceable (replace the whole assembly when they fail).
• Installation difficulty: Moderate – requires removing the deck, unbolting the old spindle (3 bolts), and transferring the pulley and blade. A torque wrench is recommended (pulley nut: 35–45 ft-lbs, blade nut: 50–60 ft-lbs).
• Common gotcha: The spindle comes without the pulley or blade. You must reuse your existing pulley – ensure it slides onto the new shaft freely. If the old pulley is rusted or deformed, replace it separately.
• Bearing noise: Some units arrive with slightly dry bearings. Spin the shaft by hand before install; if rough, add a dab of grease to the top bearing seal.

Should You Buy It

If you need a budget-friendly replacement for a worn spindle on a Cub Cadet or Troy-Built 50-inch zero-turn, this is a reliable pick. It’s not for commercial use (bearings will wear faster under daily heavy cutting), but for residential mowing, it matches OEM performance at half the price. Skip it if your deck has a different bolt pattern or shaft size – measure first.