On the previous model cleaning and lubricating the auto hubs is not
complicated althoug the manual suggests otherwise. It actually solves
most engaging/disengaging problems.
Don't know on the later model. Give it a try.
Good luck,
Erik-Jan.
--
http://www.fotograaf.com/trooper

It depends when in 98 your vehicle was made. If it is the late 98 new model
trooper read on.

I don't think cleaning the hub bearings on this model will make any
difference, anyone with more knowledge please correct.

I have a late 98 trooper which with 4WD activated by a push button on the
dashboard. Having serviced the hubs on mine for similar reasons I believe
the hub to be a simple splined stub axle and wheel bearing arrangement and
that the front wheel engage/disengage mechanism is in the axle and solenoid
operated. The solenoids control which side of a diaphram located on the axle
vacuum is applied to. The diaphram engages and disengages the drive.

Originally my trooper was not engaging 4WD at all (I found out when I got
stuck). I had thought that the 4WD light flashing slowly was an indication
that the car was in  4WD this was not so. The front axle was not engaging,
the engagment (on the front axle) is activated by two solenoid valves on the
front axle, you may be able to check whether these appear to be working by
having someone operate the switch whilst you listen carefully to them, they
should make a very slight click and both the solenoids need to operate as it
is a changeover. If this is inconclusive it is not a big job to remove the
solenoids and bench test them. Label all the rubber pipes going to the
solenoid clearly as to which pipe on the solenoid. remove all pipes,
disconnect power plug and undo two nuts. With the solenoids off I used a
9Volt battery with flying leads inserted in the sol. plug to activate it.
They were jammed due to corrosion inside, I bought new at £70 odd then found
out it was possible to open and repair with persistence. Applying voltage
activates a coil embedded in the case of sol. moves a plug in a bore. There
is a common pipe into the sol. depending on where the plug is air will flow
from one of the other two pipes. (simple pneumatic change over solenoid).

When I replaced the solenoid 4WD engaged OK initially  dropped in and out of
4WD at random particularly in winter. Later investigattion showed a poor
earth to be the problem. Prior to my ownership someone had disconnecte the
earth which went from the control circuit direct to the solenoid plug and
picked up a local earth on the axle which given the way axles are fitted
with springs, rubbers etc. was unreliable . I reconnected the original wires
and have not had a problem since.

The engagement of 4WD is complicated, there are solenoids and sensors on the
transfer box as well. I would check electrical connections to all them. It
may also be a sensor giving an erroneous reading, Your vehicle may be in 4WD
but a faulty sensor is telling the control circuit it isn't.

I did write up what I did and found. If you need any more help please post
and I will try to help.

David