Trailblazer vibration/hum

My 2002 TB LTZ 4wd (120k miles) developed a hum noise in the drivers side front end after a 5 hour drive in 4wd in a snowstorm. I noticed a slight vibration though the floor after this trip a few weeks ago and it has slowly gotten worse. I happens during accel, decel, coasting, ect. Its not tied to enine speed but chanes volume with vehicle speed. The noise is loudest around 40mph. It doesn't change when switching to 4wd. No noticeable change during lane changes. I tried rotating tires...no change in noise. I noticed a wobble in the drivers driveshaft so I replaced it, not fixed. As a last ditch effort I replaced the next most common item (in my mind), the hub. I fear it's internal to the front diff. So I'm out of ideas and don't want to just keep throwing parts at it. Any ideas?

Pretty sure your noise is from the diff. I worked on an 02 t-blazer with the exact same noise as you describe. Thought for sure it was a hub, but after pulling the diff and taking it apart, found the pinion and side axle bearings and races chewed up. Have you tried draining some of the fluid to check for metal?

The wheel bearing usually would be more common here, I have replaced a few in my shop at about this mileage, see if there is any play in the wheel/hub assy. first.

I did change the hub/wheel bearing assembly and no luck. How tough was it to remove the differencial? I've done a bunch of engine swaps and tranny swaps before so I expect it wouldn't be too bad. But I've never seen an axle go through an engine's oil pan before. Are there any special tools needed to take it out or apart? I have a helms manual for it for a guide.

It is a pain in the a** to get the diff out. Axles come out first. Then on the pass side, you need to remove the actuator from the side of the oil pan. Then there is a shaft that goes through the oil pan to the diff which needs to be pulled out (has a threaded hole in the middle for a bolt and a slide hammer usually pops it out fairly easily). Then the diff needs to be unbolted from the side of the oil pan and tied off to the side since you can't fit it out yet. The oil pan must come out first, then you can lower the diff. Like I said, a real pain in the ass.

Thanks for the help guys. I ended up figuring it out... no diff problems! :biggrin: After having 3 different people drive it and sit in passenger seat, everyone agreed that it felt like the vibration was from the drivers side. After replacing the drivers side hub there was no change. After a bunch of reading on this site and another one I found that a passenger side hub problem can feel like a vibration on the drivers side. For a sanity check I then put that hub on the passenger side and that fixed the vibration.I almost brought it to the dealer out of desperation but I dodged an expensive bullet with this one.