[AT] AC D-14,15,17 Power steering workings?

[carl gogol]

The first D-14 I bought did not have power steering and since I was 
expecting to get a front end loader on it someday, I found a used poser 
steering setup and set it aside about 6 years ago.  Finally "got-round-tuit" 
this year as  the front main seal leak was not healing itself and the whole 
front of the tractor has to be removed to do this job.  Rebuilt the assist 
cylinder and figured the control valve should get new seals and o-rings too. 
Much to my surprise, when it came apart I did not understand how it worked. 
It looks a lot more like a standard cylinder control valve then I had 
imagined.  As far as I can tell, the only thing that actually changes oil 
flow is a linear displacement of the spool.  The steering shaft passes 
through the spool, but the spool is trapped  on the steering shaft between 
two thrust bearings.  The manual's instructions are to tighten the nut that 
sets the thrust bearings preload load to 60 Ft.-Lbs, then back the nut off 
two flats and stake.  I think that my question is -- Is this limited motion 
say 0.025" to 0.050" all it takes to assist steering?  Is the resulting 
reaction of the worm gear against the sector gear enough movement to provide 
steering?  Does anyone understand this steering system and have some 
experience with it?  I had one friend tell me that this was called a torque 
multiplier system and similar to the Char-Lynn add on systems.
Carl Gogol
Manlius, NY
AC 170D
(2) AC D-14, AC 914H
Simplicity 3112 & 7116
Kubota F-2400