618-04126 918-04126 Spindle Assembly 618-04125A, 918-04126A, 918-04126B, 918-04125, 918-04125A, 918-04125B Replace for MTD Cub Cadet for Troy Bilt RZT50 LT1050 50" Deck Lawn Mower 1120370

What It Is

This is a replacement spindle assembly for the 50-inch cutting decks found on select MTD, Cub Cadet, and Troy-Bilt zero-turn and lawn tractors. The spindle houses the bearings and pulley that drive the blade, and it’s the core component you replace when the blade wobbles, the deck vibrates, or the spindle seizes.

Fitment & Compatibility

Before buying, confirm three things:

• Deck size: This spindle is designed for 50-inch fabricated or stamped decks only. It will not fit 42-, 46-, or 54-inch decks.
• Model series: Fits MTD-built Cub Cadet RZT50, LT1050, and Troy-Bilt models using a 50" deck. Cross-reference your machine’s model number with OEM part numbers 618-04126, 918-04126, 618-04125A, 918-04126A, 918-04126B, 918-04125, 918-04125A, or 918-04125B.
• Physical check: Measure the spindle shaft diameter (typically 5/8”) and the bolt pattern (two bolts, 3” center-to-center) on your old spindle. The pulley diameter is 4.5”. If your deck uses a different bolt spacing or shaft size, this will not fit.

Key Things to Know

• Quality: This is an aftermarket replacement, not OEM Cub Cadet. Users report it’s equal to or better than OEM for durability, but check the bearing seals for grease retention before installation.
• Installation difficulty: Moderate. You’ll need a jack or blocks to lift the mower, a socket set, and a puller for the pulley if it’s seized. Expect 30–60 minutes per spindle.
• Common gotcha: The spindle comes with a new pulley, but you must reuse your old blade adapter or mounting hardware. Also, torque the two mounting bolts to 25–30 ft-lb—overtightening can crush the housing.
• Match the part number: The listing covers multiple superseded numbers, but if your original spindle is 618-04125A or 918-04125B, this is a direct swap. If your original is a different series, measure first.

Should You Buy It

If your 50" deck spindle is worn, noisy, or seized, this is a solid, cost-effective replacement. It’s ideal for DIY owners who want a reliable fix without paying OEM prices. Skip it if you need a spindle for a different deck size or if you prefer OEM parts for warranty or exact-match reasons.