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About a month ago my trailblazer developed this new features. When you get into the car and start driving, everything feels completely fine. Then after about 5 minutes you start noticing slight vibration (very slight, just feels like something isn't quite right). After about a 20 minute drive, the vibration is very noticeable. By that time, it almost sounds like low engine rumble, but its pitch and volume vary directly with car's speed, not engine speed. When it gets to that level, it is also easily felt in the steering wheel.

Three weeks ago, I jacked the car up and noticed that there was a ton of grease spewed around passenger side CV boot. So I went through the motion, which took a while for various reasons, of replacing passenger CV shaft and while in there, also rebuilt 4WD disconnect with fresh bearings and seals. Yesterday I put the car back on the road and the vibration is still in there unchanged.

I tugged on both wheels to check wheel hubs and at first glace the wheel bearings appear fine. I've had bad wheel bearings on this car before, left one is 5 years old. right one is 1 year old. Whenever wheel bearings were bad a) vibration would be constant through out the drive (i.e. you can feel it the second you start driving) and b) they would change in sound when turning left or right.

This current vibration is... 1) unaffected by turning left/right or going straight 2) does not change in sound if 4wd is engaged or disengaged 3) unaffected by putting the car in neutral and revving the engine

I also checked the front differential fluid level (obviously destroying the fill plug in the process) and topped off the oil level. It was a little low, but no where near empty.

Any ideas what would be causing it?

UPDATE: Drove the car to work today. I have to take back (1) from above. If I turn the steering wheel right, vibration becomes stronger and if I turn left it gets weaker, which is actually consistent with driver's side wheel bearing being bad. The difference is that with my previous bad bearings, I only had to apply slight pressure to the steering wheel to hear sound difference, but this time, I have to push the steering wheel a bit further out (can still hear difference in a single lane going straight). Also the vibration this time seems to be distinctly lower pitch than the ones I've heard in the past with wheel bearings, but maybe they come in different shapes and sounds?

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2 Answers

I also have a AWD Trailblazer, and low diff oil can cause uneven gear wear (mine is perennially low because I have a leaking diff seal which the dealer can't get out). As the oil heats up, the vibration can become more prominent because the thick oil is no longer damping the vibration.

You may also want to check that your wheels are balanced. You might have chucked a wheel weight or worn a tire unevenly. But, the noise you describe (through the steering wheel) definitely sounds to me like a worn front diff.

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Nick, although I appreciate a response, that is sooooo not what I wanted to hear :). Stupid TB. I did have the same suspicion, that' why I topped off the fluid, but I can't say it was that low. And btw, I did also notice that the differential pinion seal is leaking oil on my car as well. Stupid TB. –  DXM Jan 16 '12 at 20:44
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It was driver-side wheel bearing.

I've had 4 other bad wheel bearings (2 in this car, 1 in wife's BMW 330i and 1 in my old Integra) and they've always sounded the same. Smooth, mid- to high-pitch vibration which almost disappears when you turn the wheel one way or another.

What confused me was this noise was much rougher (like I said in original question, almost low engine rumble) and at first it happened at any steering wheel angle. Past few days I did notice change in pitch/volume when moving the steering wheel but it wasn't like that at first.

One clue that told it it was probably a wheel bearing was after I came home few days ago, I felt the rims and driver side was significantly warmer than passenger side, which I would guess caused by extra friction in the bad hub.

Now the car is back on the road and feels as smooth as butter.

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