Blazer 4x4 problem

Hi All

I have problem with my 4WD (Blazer 4.3 LS 2000 year) turning on. I can turn it on but after driving less than 100m it switch of with noisy bang. After driving some meteres (50-100m) 4WD was disconected with strong bang. After turning of 4WD and turning again on the same has happened. I can repeat it any time I want.

And I have one (maybe stupid question) - how 4WD is being kept turning on? Is it only air pressure or any mechanical lock? If only air pressure it seems to be air problem (actuator or so on) if mechanical lock maybe the lock is broken?

I have discussion with my mechanic (it is second Blazer he ever saw, but he knows Jeep Cherokee). Whe I left my car at mornig he notices that this rubber ball (what was it - actuator?) tried to pull cord to turn 4WD on but not enough. He decided to move little this rubber ball and the it started to turn 4WD on but after short drive 4 WD turned off with strange noise/bang. And now I do not know if:
1) any air pipe, actuator or switch is bad and is not enough air pressure to turn 4WD on and keep it on?
2) any part of front diff is broken and 4WD can't be kept on

Any idea? Any advice? How to check? This rubber ball all the time tries to move cord to switch 4WD on but I do not know how to check if movement or strenght are proper. Please help!

Is it broken diff, or actuator, or hoses or vacuum switch? And what is it this rubber ball?

Marcin

First is this a 3 button 4wd dash switch - no Auto position - most LS are. If so its a 233 case and a 3 port vac switch on the transfer case that controls that front actuator. Go under hood drivers side and check the vac lines 5/32" and see if good. The last in line is plastic to the heater controls so find the other rubber one that goes down under the vehicle and thats the vac switch feed. Cap the source end off with a rubber cap or a section of hose and golf T and see if it stays in 4Hi and then you can find the cause (go to "How To" section for info.

Hi

You are right, my Blaze has no auto 4WD. I have to try what you told. Maybe important information is that light indicator works OK and after switching to 4Hi proper light is on - no blinking.

Marcin