1990 Blues???

[Rheinhardt]

I have a 1990 Blazer / 4WD / auto trans.

It has a floor shifter to go from 2WD to 4WD that incorporates a 'light' panel.

After starting up, I have to sit and wait until the upper portion of the light panel lights up (denoting 2WD) before I can drop into gear and drive. If I do NOT wait until the panel lights up ... I expirence a whole bunch of crunching & grinding noises!

In the winter... the left front axel seems to 'kick' in & out of engagement... (?)

I can, however, move the floor shifter into 4WD (without any lights) and go... once the light comes on I can shift to 2WD w/no probs...

If I do not wait until the light comes on in 2WD... I get a howling / whining / clunking sound!

Any time I am in 4WD there is a lot of noise coming from the front end... this may be a 'given'.

My thoughts are that this system may very well be 1) a vaccum system or 2) an oil dependent system both or either relying upon a pressure switch...

Either way... the right front axel is hanging up during engage / disengage.

Is there a vac hook up? Where is it? What does it rely upon?

Any help would be MOST appreciated...

TIA

R