4WD Yellow knob won't release.

Hi there,
Have just changed over my engine - dead Perkins 4203 for less dead (working) 4203 was was out test driving. I decided to lock up front freewheel hubs to check 4WD and all is good. When I came to disengage 4WD, realized that there is no load on the spring, and it therefore will not pop-up like it should.
I'm assuming that the chap who switched the engine over for me has either forgotten to put in a piece the spring can "load-up" against, or something else...
....any ideas ?
I have tried to pull it out, but don't want to force anything.
Any help appreciated
amblik

have you pulled red lever back

Yes, sorry, have done the low-range/high-range "back n forth" but it's still depressed.
As I said, there seems to be no load on the spring, which I'm almost certain there should be ..... otherwise why put it there ?
amblik

if it wont pull up it is because outer shaft behind tin cover on front of output housing is siezing in housing

James,
Many thanks for your diagnosis - is this a relatively easy fix? or am I taking the unit apart ?
amblik

should be able to fix the shafts pivot about yellow knob shaft and need to move freely through ali housing make sure when tin cover off you fit yellow knob pin in center shaft hole before working red lever to much

sounds simple enough - many thanks, will try.
amblik

That spring needs to be under load pushing up against the yellow knob, else it probly won't pop up. One end pushes against the yellow knob the other end against a small plate on the tranny tunnel. A New spring will also help, as they weakenover time.
Ad

Probably the standard combination of rust, crud, and lack of maintenance. Comes as standard with old series motors.