I wonder if the clutch out of a 1806 was much different than the 1x8's.
My first Cub Cadet was a "148" built from a 86, and I tried everything except a new spring to keep that clutch hooked up!!
The clutch would just slip in third gear. Very disappointing build.
I did ask a lot of that tractor though,,,
It may have been due to my fluid filled tires, lots of inertia to overcome.
My QL 1000 will do more than the 148 would do.