Deere 2320 pto shaft turning slowly ?!

[mx125]

I recently replaced drive shaft and output shaft for second time from dreaded u joint failure.

All seemed fine after. Today using brush hog… all good, but after period of time cutter was slowing and see that pto shaft slowing to crawl. Lift cutter and wait and ramps up again. Engine rpm was fixed. I did not know this was possible !! I thought the engagement literally moved a gear and locked to engine rpm. Ie it either moves or it doesn’t. Not a fluid connection. Any ideas at all ? Did i do something on hydrostatic transmission side ? Very confused and concerned.
Thanks.

 

[MTGreen]

I would suspect your PTO clutch if it's slowing under load.
Check the Deere parts catalog under PTO CLUTCH AND SHAFT - ST149818

 

[Roadworthy]

I'll agree withe the clutch assessment. The PTO does not drive directly from the engine. I was advised by a mechanic to depress the clutch when engaging or disengaging the PTO to prevent damage or wear on the gears. I do not know if the HST is involved or not. I've never depressed the clutch then tried to go. Perhaps I should try that. If the HST is through the clutch as well it will start slipping, too.