1998 Blazer Loud whining/howling sound

[HD2NV]

Maybe someone has posted this problem before but I couldn't find it when I searched around.

My 1998 Chevy Blazer 4X4 with 68k miles makes a loud whining/howling sound:

It sound as though it's coming from the drive train on the highway. It happens only on trips over 1 to 2 hours and sounds exactly like the loud whining semi tires make on the highway. It stops when I slow down to almost walking speed. Then there is a 'thunk' sound and it stops.

Thinking there was a correlation to the tranny, the last time this happened I stopped and engaged the '4X4 Hi', which also made it stop. It seems almost as though the 4X4 is trying to engage when in 2X4 mode.

Any ideas?

[rlith]

Sounds like your hub bearings.

[swalt]

Do some searching on the vacuum switch located above your transfer case and you have likely found your problem. It is the axle trying engage/disengage. Just don't let it go too long. Mine got so bad that it eventually would grind as I came to a stop. Sheared the gear on the front axle.

[HD2NV]

Originally Posted by swalt

Do some searching on the vacuum switch located above your transfer case and you have likely found your problem. It is the axle trying engage/disengage. Just don't let it go too long. Mine got so bad that it eventually would grind as I came to a stop. Sheared the gear on the front axle.

Do you think I need to replace the switch or just plug a vacuum line back in?

[swalt]

Originally Posted by HD2NV

Do you think I need to replace the switch or just plug a vacuum line back in?

Replace the switch.

[mtrotter70]

Check your vacuum lines also, starting at the vacuum ball and all connections.
It could be a cracked vacuum hose or bad connection.

[HD2NV]

Originally Posted by swalt

Replace the switch.

I just wanted to say thanks. As near as I can tell the switch was the problem. When I took it out the lettle ball bearing was stuck clear inside the switch. It hasn't made the noise since then. I am going to drive it on vacation next week so I'll know shortly if that was it or not.

Thanks, again.

[chigger23]

Originally Posted by HD2NV

Maybe someone has posted this problem before but I couldn't find it when I searched around.

My 1998 Chevy Blazer 4X4 with 68k miles makes a loud whining/howling sound:

It sound as though it's coming from the drive train on the highway. It happens only on trips over 1 to 2 hours and sounds exactly like the loud whining semi tires make on the highway. It stops when I slow down to almost walking speed. Then there is a 'thunk' sound and it stops.

Thinking there was a correlation to the tranny, the last time this happened I stopped and engaged the '4X4 Hi', which also made it stop. It seems almost as though the 4X4 is trying to engage when in 2X4 mode.

Any ideas?

Have them check the Spider Gear

[blazer43314]

Do you have to take the transfer case off to get to the vacuum valve?
I'm having the same noise (goes away for awhile when you go in and back out of 4x4) then comes back 10 min. later.
I've looked and felt around, found the vacuum hose, goes to the top of the transfer case. Can't see how to get the valve out without taking the case off.

[swalt]

Originally Posted by blazer43314

Do you have to take the transfer case off to get to the vacuum valve?
I'm having the same noise (goes away for awhile when you go in and back out of 4x4) then comes back 10 min. later.
I've looked and felt around, found the vacuum hose, goes to the top of the transfer case. Can't see how to get the valve out without taking the case off.

The vacuum switch is on top of the transfer case and should just unscrew. Very simple.