stepper motor internals and drive slipping help

[rally.sport]

hi all
today ive had to strip my x axis motor from the machine
its a big professional router (2.5mby1.5m) the motor is about 4.5 incehs diameter and 8 incehes long with a biult in encoder. they are 4 wire or power 1 earth and 2 encoder wires.
when stripped its assembly is: (ill describe it as best i can)
centre shaft
bearing at one end and 75% along shaft located by dowls and circlips
between bearings 4 flutes on shaft
flutes are used to locate 4 independant segements these provide drive to the shaft via the elctro magnetic forces of a stepper motor each sement is a 1/2out of step from the next.

my problem is this
during operation of the motor when loaded the 4 sements move along the shaft until one falls off anf then drive is lost.
(when no load it may work ok a quick trial was fine then refit and quick trial ok ie 10mm movements each time then a 50mm move resulted in fail the x bridge moves freely and there are no issues i can ind mechanically)
ther is no mechanical failure, to move the segments back along takes a good deal of force in a press, the problem arose after a failure of a computer controller and emplying a proessional to repair who we sacked and then used mach3 and made our own control board (our machine has parker cards which switch open circuit and closed circuit 10v not ttl via breakout board)

any one had a simialar experiance or can offer up ideas

my thoughts are its a magnetic force problem possible one segment reversed magnetised? needs lots of force to move along the shaft.
thanks in advance

[rally.sport]

yes my keyboard is broken hence hte missing letters!
i took a flat fist puch and now the w to the y x to th n bit is intermittant! lol
next time the puppet gets it