618-06978 918-06978 Spindle Assembly for 54" Mower Deck Cub Cadet RZT-L54 RZT-S54 ZT1-54 XT1-GT54, Troy Bilt TB2454 Mustang 54 XP, MTD Craftsman Z6900 Z6600 T310 G8600 G8400, with Nut

What It Is

This is a replacement spindle assembly (OEM part 618-06978 / 918-06978) for 54-inch mower decks on select Cub Cadet, Troy-Bilt, MTD, and Craftsman zero-turn and lawn tractors. It houses the pulley and bearing that spin the blade; you’d buy it when a spindle seizes, wobbles, or makes grinding noises.

Fitment & Compatibility

Before buying, verify your deck is exactly 54 inches (not 50” or 60”) and that your mower model is on this list: Cub Cadet RZT-L54, RZT-S54, ZT1-54, XT1-GT54; Troy-Bilt TB2454 Mustang 54 XP; MTD/Craftsman Z6900, Z6600, T310, G8600, G8400. This is an OEM-style replacement, not a universal part. Measure the bolt pattern (three holes, roughly 3.25” center-to-center) and spindle shaft diameter (approximately 5/8”) to confirm. If your deck uses a different pulley offset or bearing size, this won’t fit.

Key Things to Know

• Quality: 4.4 stars from 38 reviews—generally good, but a few report premature bearing failure. Inspect for smooth rotation before installing.
• Installation difficulty: Moderate. You’ll need a socket set, torque wrench, and possibly a puller to remove the old spindle. Budget 1–2 hours.
• Common gotcha: The nut included is for the blade, but you may need to reuse your existing pulley nut or key. Check your old setup.
• Deck removal: You’ll likely need to remove or tilt the deck to access the spindle from below. Have a jack or blocks handy.

Should You Buy It

If you own one of the listed 54” deck models and need a direct OEM-style replacement without chasing universal fits, this is a solid choice at $30.99. It’s best for DIYers comfortable with basic mechanical work and looking for a reliable, drop-in fix rather than a premium upgrade. Skip it if you’re unsure of your deck’s exact spindle pattern or want a heavy-duty aftermarket unit.