John Deere M126009 Transmission Drive Belt Fits LT155 & LT166 Mowers

What It Is

The John Deere M126009 is a factory-spec transmission drive belt that transfers power from the engine to the hydrostatic or manual transmission on LT155 and LT166 lawn tractors. It’s the belt that moves the mower forward and backward, not the deck belt.

Fitment & Compatibility

• Exact fit for: John Deere LT155 (1994–2004) and LT166 (1995–2003) models. Does not fit other LT-series mowers without modification.
• Deck size: Works with any deck size (38", 42", 48") on these two models—deck size doesn’t affect transmission belt fitment.
• OEM vs aftermarket: This is an OEM John Deere belt (M126009). Aftermarket equivalents exist (e.g., Stens 180-136, Rotary 13016), but verify cross-reference before buying.
• Measurements: Belt is 3/8" wide x 92.5" effective length. Measure your old belt end-to-end (not around pulleys) to confirm. If it’s shorter or longer, it’s the wrong belt.
• Check your model number: Look for a tag under the seat or on the frame. LT155 and LT166 are common, but some variants (e.g., LT155H) use the same belt. LT150, LT160, or LT170 do not.

Key Things to Know

• Quality: OEM belt lasts longer than most aftermarket belts—expect 3–5 years with normal use. Aftermarket belts may squeal or wear faster if not exact spec.
• Installation difficulty: Moderate. You’ll need to remove the belt guard, release tension from the idler pulley, and route the belt around the transmission pulley and engine pulley. A diagram is helpful—take a photo before removing the old belt.
• Common gotcha: The belt can slip if the idler pulley spring is weak. Check the spring and pulley for wear before installing the new belt.
• Don’t confuse with deck belt: This belt drives the wheels, not the blades. If your mower moves but blades don’t spin, you need a deck belt, not this one.

Should You Buy It

If you own a John Deere LT155 or LT166 and your mower won’t move, or the transmission belt is cracked, frayed, or stretched, this OEM belt is the right choice. It’s a direct fit, reliable, and priced fairly for genuine John Deere quality. Skip it if you have a different LT-series model or an aftermarket belt that meets the exact 92.5" x 3/8" spec and you’re on a tight budget.