Hi and
to the forum.
As far as I'm aware, no one on the forum has replaced the axle on the MPIII, but it appears to be pressed into a steel sleeve with a key-way slot which receives the locating key.
The axle looks as if it has been fitted from the controller side of the stator, and it has a circlip fitted on the opposite side to ensure that it cannot slide out if the fit becomes too loose.
This circlip
(see picture below) must be removed before you can attempt to gently tap
(or maybe press) the axle out.
If the axle is machined for a precise sliding fit
(transition fit) it may be possible to simply remove it with a wooden or copper mallet by gently tapping the R/H end of the axle.
However, if it has been machined for an interference fit, it would have needed a lot of force to press it into place. If this is the case, it will probably need to be pressed out again using either a mechanical or hydraulic press, ensuring a suitable piece of tube is placed over the axle on the controller side
(seating directly against the steel insert) to oppose the applied force of the press.
The inner diameter of the tube would ideally be very slightly larger than the outer diameter of the axle where it seats against the stator inside the controller housing.
If the inner diameter of the support tube is too large, the steel insert will not be properly supported on the tube, and the large force exerted by the press would then act upon the body of the stator casting instead. This could result in the stator assembly becoming damaged
(and unusable) if the force applied to the axle was sufficient to break the joint between the steel insert and the stator.
Have you made enquiries as to whether GM are willing to supply just the steel axle?
Alan