When cutting hay pto suddenly started stopping unexpectedly. First time or two I thought I had bumped the knob as it would start turn on as soon as you retried it. I pulled apart the solenoid and modulator valve and cleaned them out as I suspected debris in them as a brake lining let go and filled everything with filings before I found it and replaced it.
When that didn’t solve the problem I observed closer and there was a slight buzzing sound and pto seemed to be trying to turn. After researching forum I read Haybaler’s account of the worn end of the pto shaft and found same issue. 6800 hours lots of 540 work only have used 1000 couple times.
I just built up the end of the pto shaft where the piston pushes on the shaft with JB weld and replaced the snap ring holding in the pto and have had no problems for the 5/6 hrs I’ve used it. It might not be a long term solution but it’s a easy fix. Takes overnight for the JB Weld to harden. I built it up almost 1/8” and then used a Dremel to trim it to a button as it has to fit in the hole with the piston. I originally tried a disc on the end of the shaft before I discovered there isn’t room between the end of the shaft and the piston housing it needs to be the same size as the piston plunger.