M45123 Deck Idler Tightener Spring, Fits for John Deere 318, 316, 317, 322, 330, 332 & 48"/54"/60" Decks | for John Deere Mower Deck Tension Spring Replacement​

What It Is

The M45123 deck idler tightener spring is a replacement tension spring for John Deere lawn tractor mower decks. It maintains proper belt tension on the idler pulley, preventing belt slip or throw during mowing.

Fitment & Compatibility

Before buying, verify these three things:

• Model: Fits John Deere 316, 317, 318, 322, 330, 332 (gas and diesel).
• Deck size: Works with 48", 54", and 60" mower decks.
• OEM cross: This is a direct replacement for OEM part M45123. Measure your old spring’s overall length (unstretched) and coil diameter—this spring is roughly 3.5" long with a 0.5" coil ID. If your deck uses a different spring (e.g., on some 42" decks), it won’t fit.

Key Things to Know

• Installation difficulty: Easy (15-30 minutes). Requires a flathead screwdriver or spring tool to hook ends onto the idler arm and deck bracket.
• Quality: Aftermarket steel spring with zinc coating—resists rust but not stainless. Matches OEM tension specs.
• Common gotcha: If your deck has a broken idler pulley bracket or worn belt, replace those too. A new spring won’t fix worn hardware.
• Belt routing: Before removing the old spring, take a photo of the belt path. The spring hooks to the idler arm, not the belt itself.

Should You Buy It

If your John Deere 300-series tractor with a 48-60" deck has a loose or missing belt tension spring, this is a cheap, direct-fit fix. It’s ideal for DIY owners who want OEM-like performance without dealer markup. Skip it if your deck has bent arms or a damaged pulley—you’ll need to repair those first.