'01 sonoma 4wd won't engage

Vehicle: 2001 GMC Sonoma sls ext cab 4.6L

Problem: 4Hi and 4Lo won't engage, Low xfer case engages but front wheels don't.

Symptoms: When I bought this truck used I noticed that after engaging 4Hi
there was a vibration around 50-65mph. After 20-30 miles the vibration would
go away.

Didn't use 4Hi/4Lo for quite a while.

After recent snow storm when I tried to use 4Hi. Upon disengaging there was
an oscillating vibration that would lower in frequency until stopping front
wheels. When accelerating noise is not heard, only when coasting or decelerating. At this time the vehicle was out of 4wd. Vibration did not go away after 20-30 miles.

Just the other day after another snowstorm, I tried the 4Hi/4Lo and it won't
engage 4WD only low range. I get ONLY a click for 4Hi and a click and a clunk
for 4Lo. Seems as though I get the low range but the front axle won't engage.

When engaging the 4Hi and traveling 5-10 miles I heard an occasional couple of knocking noises from what appears to be the right front wheel/hub. Pressing 2Hi button stops these random knocking noises.

The lights corresponding with the buttons on dash work properly i.e. 4Hi lit
when 4Hi pressed and 4Lo lit when 4Lo pressed, 2Hi lit when 2Hi pressed!

What suggestions does anyone have and what should I check for?

thanks

Check for bad wheel bearings and rotors and caliper mounting and loose wheel lug nuts.
Check for Axel joints and drive shaft u joints and splines.

Is the noise in 2W or just 4W?

Is front Axel locking in good and unlocking good?

front axle won't lock into 4 wheel drive

noise used to be only in 4wd but beings I cant get into 4wd don't know

will checl other things and get back to you

going to check some kind of actuating diaphram under battery box too

thanks for reply

Any noise in 2W?

Any noise in 2W?

Upon disengaging 4WD (when I could engage it last) there was
an oscillating vibration that would lower in frequency until stopping front
wheels. When accelerating noise is not heard, only when coasting or decelerating. At this time the vehicle was out of 4wd. Vibration did not go away after 20-30 miles.

Noise was still there before last storm, but will try to check again today along with other stuff you recommended.

In 2W Noise on coast points to rear rear end problems
Open link and go to rear end noise.

http://www.differentials.com/install.html

http://www.differentials.com/diagnose.html