95 S10 Blazer drivetrain noise in 2HI

[mtrotter70]

My 95 S-10 Blazer started making a loud humming noise when driving in 2HI. It has the electronic shift 4X4. The noise really gets loud when slowing down and sounds like a loud siren or horn. The noise is not noticeable at highway speeds.
The sound seems to come from the front end towards the right side. The wheel bearing hubs are ok.

When I shift into 4HI the noise goes away. I used to be able to switch back to 2HI and the problem would go away for a few days. Now 2HI always has the noise at low speeds. The 2HI light on dash does not stay on in 2HI also, although I can hear it shifting - probably just a burned out bulb but not sure.

I've heard this problem could be caused by a bad vacuum switch on the transfer case but not sure if it has one since it has the electronic shift. Can anybody help me out please?

Your help is greatly appreciated.
Thanks,
Mark

[ctaylor2]

Hey I believe I have the same type of noise that just started in my S-10 pickup but mine seems to be constant with the tires rotating and is more pronouced when leting off the gas.

Ps I would love to find out want this is also I hope someone out there can help us both.

[amac209]

i don't think the 95's use a vacuum switch i'm pretty sure they use an electronic actuator to engage the front diff. does the noise change when turning? they might be a bad bearing in the front diff.

[mtrotter70]

The problem was caused by a vacuum leak in one of the vacuum hoses.
Fixed the hose and the problem went away.
Even though it has an electronic transfer case there are still vacuum
lines/vacuum switch.