AM138220 Left Hand Rear Mower Deck Gage Wheel Arm (3/4" dia.) for John Deere X300 X304 X320 X324 X340 X360 X500 X520 X530 X534 X540 X590 48In & 54In Mower Decks, AM136329

What It Is

This is the left-hand rear gauge wheel arm for 48-inch and 54-inch mower decks on select John Deere X300 and X500 series lawn tractors. It supports the deck’s rear corner, preventing scalping and protecting the blade housing on uneven terrain.

Fitment & Compatibility

Before buying, confirm your mower deck is 48 or 54 inches and that you need the left-hand rear arm (not right-hand, not front). This aftermarket part replaces OEM AM138220 (and superseded OEM AM136329). It fits John Deere X300, X304, X320, X324, X340, X360, X500, X520, X530, X534, X540, and X590 with the specified decks. The arm accepts a 3/4-inch diameter wheel axle. Check that your existing wheel and hardware (spindle, bearings, cotter pin) are in good shape—this arm does not include them.

Key Things to Know

• Quality vs OEM: Some users note the aftermarket metal is slightly thinner or the paint finish less durable than the original John Deere part. It may bend under heavy use on rocky ground.
• Installation difficulty: Easy—remove the old arm by pulling the cotter pin and sliding off the wheel, then reverse. No special tools required.
• Common gotcha: The arm’s mounting hole can be tight on some deck brackets. You may need to file or tap it slightly for a smooth fit. Double-check you have the correct side; left and right arms are not interchangeable.
• Wheel not included: You’ll reuse your existing wheel or buy a new one separately if the wheel or bearings are worn.

Should You Buy It

If you need a budget-friendly replacement for a worn or bent OEM arm on a 48 or 54-inch X300/X500 series deck, this will work for light to moderate use. It’s not the best choice for commercial-grade abuse or rocky lawns where durability matters most—consider OEM if you want longer life. For the price, it’s a solid value for most homeowners.