ok....found this thread....& I have a new to me 1976 model JD 100 with serial ##### of 57384...the former owner told me that when u engage the PTO.....the deck blades do spin.....but when u go to cut grass..it will stall the blades...I guess there is an adjustment of the nuts #22 in the pic diagram posted by Bob...Adjusted by raisin the nuts up the shaft some. If I'm wrong....let me know... Whirly