2000 Blazer Humming Again

Hey guys. I have done the standard search on "humming" and can't really find an answer to my problem. My truck was road tested by my dealer foreman today and after a number of years of vibration/humming problems with this front end the shop is leaning toward trying to have aftermarket warranty replace the entire differential rather than tear it apart one more time (this would make number 5 teardown in 4 years) as teardown and diagnosis could be more costly than complete replacement and given the history of this diff, it has been problematic.

Here is the problem. In 2HI the vehicle will develop a humming sound similar to a bad wheel bearing which sounds like it is coming from the right front wheel around 20km/h and continue throughout speed. Upon deceleration it sounds worse from 60km/h down. Engaging 4WD eliminates the problem which tells me it is inside the diff, but upon returning back to 2HI the problem will usually come back after a short period, but not immediately.

Wheel bearings were both replaced. Actuator cable was replaced. Vacuum switch was replaced. Tires are new (problem was there before and after tire replacement) Every diagnostic test has been done on the 4WD system and vacuum system and it is functioning flawless (according to the dealer). Fluids all changed. .

Anyone have any ideas of what else to look for? I have lived with the problem for 75,000km's but just recently it has worsened and GM corporate gave me the single finger salute over the whole ordeal. Their fix under warranty was to lock the front diff by re-routing my vacuum lines (unknown to me).

i have the same problem with my 96 it is weird how long have you drove it like that with no problems besides the noise your the only person i have heard with this problem besides me

DID you replace the cv joints

DID you replace the cv joints

The dealer has been leaning toward the differential as the problem because of the fact that the humm disappears once it is engaged in 4HI. The CV joints have been out, inspected and repacked and they found no problems with them. They are working with the warranty company to try and swap in another front end (not new, but low mileage) as they have come to no other conclusion than to suggest the diff was "out of spec" and to diagnose any further is not time effective against replacement.

had bpth my front hubs done and the humming is gone.

I am living this problem with my new to me 2000 blazer that I bought the day after Thanksgiving. I took it to my mechanic initially to have him give it the once over in the post 30 day purchase period and he found no problems with it. The first time I went to use the 4WD (light winter this year of course) I found that the 4WD didn't work. Back to the mechanic who found a hose detached. He hooked it back up, test drove it and voila- the 4WD worked. Alls well, I thought. A month or so later - it started that hum you speak of - at speeds from 10-30 mph, sounding like it was coming from the right passenger front. Back to the mechanic who couldn't get it to duplicate but thought the 4WD was sticking. It clunks into 4WD -so he messed with it and proclaimed that he got it to "unstick". To make matters worse -its got snows on the rear and all seasons on the front and I've talked to both my mechanic and my tire guy about that -and they've said, "its not great - but not going to do any damage" Boy were they wrong.
Within 2 weeks now - its gone from making that hum intermittently now and again - and I can get it to stop by either pulling over, putting it in park, pushing on the 2WD button - or some variation - to nothing would make it stop and by Sunday this past week it did the hum for 2 days straight every time I took it out. Finally, I got so frustrated, I put it in 4WD and the humming stopped - but the clunking began. CLUNK, CLUNK, CLUNK, all down the road. After back and forth with that for a couple miles, I got so frustrated that I pulled over and just pushed 2HI, 4HI over and over - and then- like magic - no hum, no clunk.
Got it into my mechanic today to do some routine service and to find out what is ALSO making it creak like a rust bucket (new ball joints now) - and they're thinking differential - and oh by the way, they say, you need to have 4 new tires- all the same tread size - because that could be half your problem -which could also have caused major damage because by Sunday -the humming was starting to sound like a grinding and was from 0-40mph that I could hear it.
Bigger problem - they're keeping the car and going to test drive it tomorrow after ball joints and new tires- and if they can't duplicate the noise -the mechanic says theres no way to diagnose the differential as the problem without tearing the car apart and that could cost about $900 - and a new transmission seal, new u joints- and in the end -it could end up NOT even being the differential - they just don't know.
Is there a way to diagnose it as the differential - or could it be the front axle? Or I've heard about the actuator - or the switches- ?? Any suggestions on this would be helpful here. I'm afraid tomorrow my mechanic is going to test drive it - not get it to duplicate either the thumping in 4WD or the humming/grinding in 2WD - and proclaim it fixed with new tires- and I'm going to have major damage driving it when it is indeed something to do with the differential.
Thanks

I am living this problem with my new to me 2000 blazer that I bought the day after Thanksgiving. I took it to my mechanic initially to have him give it the once over in the post 30 day purchase period and he found no problems with it. The first time I went to use the 4WD (light winter this year of course) I found that the 4WD didn't work. Back to the mechanic who found a hose detached. He hooked it back up, test drove it and voila- the 4WD worked. Alls well, I thought. A month or so later - it started that hum you speak of - at speeds from 10-30 mph, sounding like it was coming from the right passenger front. Back to the mechanic who couldn't get it to duplicate but thought the 4WD was sticking. It clunks into 4WD -so he messed with it and proclaimed that he got it to "unstick". To make matters worse -its got snows on the rear and all seasons on the front and I've talked to both my mechanic and my tire guy about that -and they've said, "its not great - but not going to do any damage" Boy were they wrong.
Within 2 weeks now - its gone from making that hum intermittently now and again - and I can get it to stop by either pulling over, putting it in park, pushing on the 2WD button - or some variation - to nothing would make it stop and by Sunday this past week it did the hum for 2 days straight every time I took it out. Finally, I got so frustrated, I put it in 4WD and the humming stopped - but the clunking began. CLUNK, CLUNK, CLUNK, all down the road. After back and forth with that for a couple miles, I got so frustrated that I pulled over and just pushed 2HI, 4HI over and over - and then- like magic - no hum, no clunk.
Got it into my mechanic today to do some routine service and to find out what is ALSO making it creak like a rust bucket (new ball joints now) - and they're thinking differential - and oh by the way, they say, you need to have 4 new tires- all the same tread size - because that could be half your problem -which could also have caused major damage because by Sunday -the humming was starting to sound like a grinding and was from 0-40mph that I could hear it.
Bigger problem - they're keeping the car and going to test drive it tomorrow after ball joints and new tires- and if they can't duplicate the noise -the mechanic says theres no way to diagnose the differential as the problem without tearing the car apart and that could cost about $900 - and a new transmission seal, new u joints- and in the end -it could end up NOT even being the differential - they just don't know.
Is there a way to diagnose it as the differential - or could it be the front axle? Or I've heard about the actuator - or the switches- ?? Any suggestions on this would be helpful here. I'm afraid tomorrow my mechanic is going to test drive it - not get it to duplicate either the thumping in 4WD or the humming/grinding in 2WD - and proclaim it fixed with new tires- and I'm going to have major damage driving it when it is indeed something to do with the differential.
Thanks

I can sympathize with you. My truck has been at the dealer for the past week. Bearing in the front axle is gone, shaft is damaged as well as several other components. The diff is now being dismantled because of all the filings found.

In your case, the grinding is this part pictured in the front axle, likely caused by the vacuum switch on top of the transfer case sticking causing the front axle to partially engage. Make sure you replace the vacuum switch after you have all the repairs done. The vacuum switch stuck on me last year and this was the resulting damage.

http://files.automotiveforums.com/gallery/watermark.php?file=/500/116754Gear_damage.JPG