Hey does anyone have a clue what would cause the rear PTO to keep turning when not engaged on a JD 4200 HST?
Most likely your PTO brake has failed. That's a common problem. The
4200/4300/4400 uses a wet multiplate clutch for engagement, and a 3-plate
multiplate clutch for braking. It is the only tractor I have owned that has
a PTO brake and it is very prone to breakage. Perhaps that is why others
have reported the same issue. Note that these tractors with the PTO
brake engaged allow about 180-degrees of rotation of the PTO shaft to
help with getting the drive shaft on. I don't really see the need for this
brake, so it is not worth fixing, but you will likely find pieces of the brake
discs in your sump.
My Kioti's PTO shaft does spin slowly (in N) with its engine running and the oil
is cold, but that is normal (no brake).