Re: TN70 4x4 Problem
Sorry you haven't gotten any help. My D40 Case has the same system. I usually engage 4WD while standing still with the clutch depressed. Sometimes I've had to move the tractor a bit to engage -- but seldom. I disengage while still or moving with the clutch depressed.
If I was having a problem I'd check the exposed linkage first to make sure it had enough adjustment to engage. Total movement on my lever is probably 2-3".
Are you SURE that it's not engaging? You can't tell on mine unless you load it up to the point that you need 4WD ---- as in when I'm using a 6' tilling implement or in deep snow.
Toro 4225 Zero Turn
John Deere 111
McCormick Deering 15-30