If it is a cable PTO which operates from a handle there are two types I've worked on. one has not adjustment, the other has a spring which can be moved to compensate for streching of the mowing deck belt. If your mower has no adjustment than more tham likely it is the belt.
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If it is a cable PTO which operates from a handle there are two types I've worked on. one has not adjustment, the other has a spring which can be moved to compensate for streching of the mowing deck belt. If your mower has no adjustment than more tham likely it is the belt.