Thank you guys for your support and help.

I'm going to drop the truck today and I will let you know the results.

Cheers

An Update...

The last friday was pull off the diff, after opening I tried to expand the diaphragm with the actuator pump with no luck...tried with an air compressor with around 8 psi... and I could heard a zzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzz at one place of the diaphragm, let me tell you I felt kind of relaxed, because at least I had found the cause of no locking the diff.

The next day I went to a weld shop, and with the help of nprecon who gave me all the details and instructions on how to do it, the diaphargm was welded on a few minutes.

I just got back the tracker, running directly from the shop I went to a close zone to test the 4WD....ahhhhhhhhhhhhhhhhhhhh.... what a difference! I felt so happy when finally I see it working!!!

I just ordered the manual hubs to be installed on a few days more, but... today...I have a 4x4!

Thank you guys for the great help!

Cheers

Glad it worked for you, xcabo.  Taking the 'air' out of the equation is peace of mind. Things can still go wrong... however bladders leaking air and air pumps rupturing their diaphragms won't be one of them.  

I got the idea for physically locking the actuator ring in place here on the forum (don't recall his name but he is up in Canada... rally-t?? who was a mechanic and liked to run road rally races in the snow ) when he used zip ties on his diff.   Then SHADOW, here on the forum, tac welded his diff and posted up how he did it.  I liked the tac weld approach so I went with that option.  SHADOW provided me additional information details, also.  That's how the forum works.  Guys and gals sharing ideas and fixes.  Lots of them are more cost effective than the 'factory solution'.   There are a million of them and probably another million waiting to be posted.  Its all good.

Did this repair to mine more than a year ago.

I Gently pushed the actuator over with a couple screw drivers to engage the axle lock, then ran a bead of weld in the 4 recessed parts of the gear.  The axle lock has alot of material to weld to so you can get good heat penetration.
Installed new seals, axle support bushing, axles and manual hubs (cost was still lower than repairing the flawed compressor system). I have pounded the crap out of mine in mud and snow and has performed flawless for over a year.  The only thing I have done since is change the diff fluid periodically. But dont forget to jack up the front of the vehicle and get at least 1 litre of diff fluid in there.
Don't know why one would use zipties, other than the fact that welding it is a permanent fix, but that's a good thing to me.
A good weld is not gonna break like a ziptie.