My JOHN DEERe STX38 black deck would fall off every time I hit a dirt mound or unseen tree root. The two steel bars would jump over the washers above the top rear of the deck and the deck would fall to the ground. The last time it did it, it broke a one month old $40.00 belt. I fixed the problem by removing the two bolts (one on the left side, one on the right side) and replacing the two washers with larger 2" washers. I found some 1/4" x 2" washers at Ace Hardware and drilled the 1/4" holes out a little larger to fit the bolts. I actually used two of the new washers together on each bolt since two of the new ones were the same thickness as one of the old ones. The deck no longer falls off. Total cost, $1.20 at Ace Hardware.
Check your idlers on the deck as they are the most common culprit.
bladebelt diagram for john deere stx38 yellow deck
Check with your John Deere dealer. No, not Home Depot or Lowe's but an actual business that works on and sells John Deere mowers.
On the deck
How do you change a mower deck belt on a John Deere L130?Read more: How_do_you_change_a_mower_deck_belt_on_a_John_Deere_L130
here is a diagram that might be helpful: https://jdparts.deere.com/partsmkt/document/english/featbene/L120_L130_48_3N1deck.pdf
38'' deck
on the mower deck
anonymously
The John Deere 48 mower deck belt pattern diagram can be obtained from most John Deere dealerships. Many times when you purchase the belt the parts store will give you a belt pattern diagram.
Check out crigby's John Deere deck page. It shows the belt routings for most of the JD mowers. See the link below.
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