RT400 Transmissions Variaton Belt GT37419 GT79267 Compatible with John Deere AUC13704 MIA12479 D105 E100 X105 X106 100 Lawn Mower Tractors Drive Belt

What It Is

This is a drive belt for the RT400 transmission, designed to transfer power from the engine to the transaxle on select John Deere 100-series lawn tractors. It’s a direct replacement for OEM belts used in models like the D105, E100, X105, and X106.

Fitment & Compatibility

Before buying, verify your mower’s model number and deck size. This belt fits John Deere D105, E100, X105, X106, and other 100-series tractors with a 42-inch or 48-inch deck and the RT400 transaxle. Cross-reference your OEM part number: it replaces AUC13704, MIA12479, GT37419, and GT79267. Measure your existing belt length (should be approximately 92.5 inches—measure end-to-end, not around pulleys) and width (typically 1/2 inch). Do not rely solely on model name—check your tractor’s serial number and deck type (e.g., Edge, Accel Deep) for compatibility. This belt is not for zero-turn mowers, riding mowers with different transaxles (e.g., Tuff Torq K46), or older 300-series tractors.

Key Things to Buy

• Quality: RT400 belts are aftermarket, not OEM John Deere. Expect similar durability to OEM if installed correctly, but may be slightly thinner or less reinforced. Check for fraying or cracking after 50 hours of use.
• Installation difficulty: Moderate. You’ll need to remove the mower deck and possibly the transmission pulley guard. No special tools required, but a belt tensioner tool or pry bar helps. Watch a specific video for your model—routing errors cause slipping or premature wear.
• Common gotchas: The belt must be routed exactly around the tensioner pulley and transmission pulley—wrong path causes belt to flip or snap. Ensure the tensioner spring is in good condition; a weak spring won’t maintain proper tension. Also, check that your mower’s pulleys are clean and spin freely—frozen pulleys will destroy this belt quickly.

Should You Buy It

If you need an affordable, functional replacement for a worn OEM drive belt on a John Deere D105, E100, or similar 100-series tractor with an RT400 transmission, this belt is a solid budget pick. Avoid it if you want premium durability or have a different transaxle—stick with OEM for those. At $11.50, it’s worth trying for DIY repairs, but monitor it closely during the first few hours of use.