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2005 saab trailblazer_lt
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8 Posts
Discussion Starter #1
2005 Saab 9-7X Linear (AWD 4.2L) 85K mikes.

I’ve been trying, for last number of months, to track down the source of an annoying and quite prominent hum/buzz/growl somewhere in the drive-line of this damn truck ... my wife’s vehicle BTW.

I’ve replaced all drive-line fluids (front diff.; rear diff.; transfer case; transmission) with either OE GM fluids or top of the line after market synthetics.

The hum/buzz/growl persists and has recently developed a pulse that changes with vehicle speed.

After all of this, I was convinced it was crappy, noisey tires and was preparing myself to purchase a new, higher quality name brand set until I did a rotate and tire pressure adjustment/equalization this past weekend that resulted in no change.

I’ve also done the DIY “feel” test at all four wheels with zero indication of a failed/failing wheel bearing.

I then read some posts here and on other GMT related forums indicating that a “worn” hub assembly can cause these symptoms yet with no indication of a bad wheel bearing.

True or False?
 

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2004 gmc envoy_slt
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2,493 Posts
Your mileage is relatively low, but the truck is still 15 years old. I would say it is likely you have a worn hub assembly
 

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2003 chevy trailblazer_ltz
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160 Posts
When it was MY Trailblazer that howled, it was the bearings in the axle disconnect mechanism. You've got a similar--but non-switchable--system. Basically, you've got an axle disconnect that can't be disengaged like the 4WD models.

There's needle-roller bearings inside, they're under-sized for the load they carry. The races they run on get chewed-up, and they howl like mad.

In my case, I needed to repair this axle disconnect box twice. Once with a "rebuilt" assembly, the second time I rebuilt it myself using a wider bearing on the internal gear, and a new internal gear. And new seals, of course. I also needed the shift fork, but you don't have the ability to shift in and out of 4WD, so no shift fork for you.

For the record, Dorman sells (or at least used to sell) a "new" axle box for 4WD and another for AWD vehicles. It's a Made-In-China knockoff of the Genuine GM part.

Jack up the vehicle (all four wheels off the ground, safe and stable) and have someone "drive" the thing. Put a stethoscope on the axle disconnect, see if you hear the howl from it.

Exploded view in this link. Your system is towards the bottom of the page, the "AWD" version. I bet you've got bad bearing(s) (#2, three places) and perhaps scored surfaces on #5.(the piece he's holding in his hand.)

I've never had the AWD version apart, I don't know if the wider bearing fits--but I suspect it does. Seems to me the OEM bearing is 16mm wide, and the one I use on the internal gear is 20mm, just barely fits in the case. But maybe it's 12mm and 16mm. Been years since I've had to **** with mine. Anyway, two regular bearings, one extra-wide.


This is an aluminum housing that bolts and presses into the aluminum oil pan, and then gets wet with road splash. It's no surprise if they corrode together and have to be practically beaten apart. But sometimes ya' get lucky.
 

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2005 saab trailblazer_lt
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Discussion Starter #4
Much obliged for this detailed response and the service/repair link.

I’ll investigate this issue further based on your input.

Thanks again ...
 
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