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Hey guys, totally at my frustration point with this one. '08 TB 4.2 with 4x4 option. Hoping someones come across this one. Symptoms:

-"Cabin Pressure" sensation at 35 mph (similar to someone cracking a window at high speeds)
-Growling/High Pitch humming noise between 35 and 50 mph
-Violent shaking and low pitch vibration from rear passenger wheel area begins at 55, continues to 70 mph
-Affects gear shifting timing
-When I let off the gas at 65 mph, vehicle decelerates quicker than normal, does not coast.
-Difficult to maintain at 55+, feels similar to driving through high winds.
-When coasting at 10 mph, I apply hard gas pedal and can hear metal linkage noise as it falls into higher gear (coming from rear end).

Done so far:

-Brand new tires, balanced and aligned (problem existed with old tires, continues with new ones)
-Replaced U joints
-Drive shaft inspected and determined to be unbent

2 Mechanics unable to solve. Lifted truck in the air, could see violent shaking of rear passenger wheel. Got the impression they were unwilling to dedicate a lot of time to micro investigating.

Thanks in advance for reading
 

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WHAT "evidence of shaking on the rear passenger wheel" did they find and can you post that observation?

15 or 15 inch tires start their primary harmonic (imbalance hopping) at about 52-55 MPH, so this is in the ballpark of a tire imbalance problem BUT --- there's possibly more. I don't have any idea of the rim diameter of your vehicle - but 15-16 inch rims are kinda predictable - 17s & 18s are kinda new to me, but since they run approximately the same general circumference of a 15 or 16 incher, I'd say that they prolly come "in" about the same road speed too. I can be wrong here and I'm sure someone will correct my thoughts if it's so.

I'd take both shocks off the rear axle and check them out in your hands. My money's on something is askew inside one of those shocks and it's not doing it's job.
 

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Discussion Starter #3
WHAT "evidence of shaking on the rear passenger wheel" did they find and can you post that observation?

15 or 15 inch tires start their primary harmonic (imbalance hopping) at about 52-55 MPH, so this is in the ballpark of a tire imbalance problem BUT --- there's possibly more. I don't have any idea of the rim diameter of your vehicle - but 15-16 inch rims are kinda predictable - 17s & 18s are kinda new to me, but since they run approximately the same general circumference of a 15 or 16 incher, I'd say that they prolly come "in" about the same road speed too. I can be wrong here and I'm sure someone will correct my thoughts if it's so.

I'd take both shocks off the rear axle and check them out in your hands. My money's on something is askew inside one of those shocks and it's not doing it's job.

Thanks for the reply. 245/65 17's are the wheels. I just find it peculiar that the same symptoms it was displaying before the new tires, are the same it's demonstrating now.

I decided, since posting, to take it back to the tire tech for their input. They vehemently defended the tires as good working condition (the mechanics had criticized the tires for their Made In China status) and stated that the tires had passed a balance test. Conveniently, after I got the truck back, the shaking at 55 seemed to be better but at 70, a mild shake can still be felt.

I'm curious if anyone has dealt with differential or shock/strut issues with the same symptoms...
 

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I'm curious if anyone has dealt with differential or shock/strut issues with the same symptoms...
CV joints? Yes if they are dry, rusted "frozen" or bent... uh huh. But they'd more than likely also give trouble in turning.

I've never had a differential out of balance problem.
Shocks/struts? Uh huh. Did you test the rear shocks as I instructed?

Just remove the bolt/nut on each shock and slip it off the mount and try to compress - then - elongate it. That will eliminate the rears if the are awfully hard to compress and they dont move easily.

The fronts are trickier ... but can be tested although you'll have to sign a waiver for me for the instructions.

OR ....tell you vehemently denying dealer that you're OK with the tires if they can find the problem in one move. Don't let them put you up against the wall and force you to be the recipient of their parts canon. If they hand you a blindfold, be very suspicious. .
 

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While you have your TrailBlazer up on jack stands to test the shock absorbers and you've removed the wheel and rotor to inspect the emergency brake shoe, put the transmission in neutral and move the drive axle flange by hand to see how it feels. After the initial clunk, does it feel rough when you turn it? Does it move up and down more than a fraction of a hair? Repeat for the other side. By doing this, you are checking the rear wheel bearings.
 
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