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2008 Chevy Trailblazer
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Discussion Starter · #1 ·
Hello all, I have a 2008 Chevy Trailblazer 4.2L 6- Cylinder 4x4. It just rolled over 80,000 miles. The problem I am going to describe has been happening off and on for probably the last 30,000 miles, but never consistent enough to troubleshoot. Currently it has been doing it more and more often, and I have been troubleshooting some.

The Problem:

Randomly, while driving, the car shakes. The steering wheel vibrates / shakes / moves a small amount back and forth at a fast rate. More often than not this problem feels like it is in the front end / steering. At times all the shaking is in the rear end of the vehicle and the steering wheel does not move. Other times the rear and the front end / steering wheel shakes. When this issue is not happening, it drives smooth and beautifully.

I do not feel anything in brake pedal, but when this happens and I apply the brakes, at times it feels like car is breaking hard and then soft and then hard and then soft while pressing on the brake with the same force. I guess pulsating possibly? The brake pedal is not vibrating.

This problem seems to start acting up randomly too. At times even while driving with cruise control and never having touched the brake pedal in miles. It does this at a variety of speeds and severity does not change with speed. Sometimes the severity is pretty mild and its a light shake, and other times it is worse and it feels like I am driving down a washboard road.

Temperature outside does not seem to affect this, neither does vehicle temperature or how long I have already been driving. It has done it just starting out on a trip with a cold vehicle, as well as after 3 hours of driving where everything is at operating temperature.

The longest time this went on was ~5 miles of driving, generally this lasts for a mile or two and then goes away and it is back to driving nice and smooth. Sometimes it does it as much as 3 or 4 times during a 300 mile road trip, other times I can go several hundred miles to a thousand miles without it ever acting up.

I am at a loss for why this comes and goes and the severity is random too, as well as the fact that it feels like it moves around from the front end, rear end, and both.
This leads me to believe something in the ABS system is acting up.
There is no ABS light coming on during this, and no codes are being stored in the computer.

Things I have checked:
-Tires are good, not out of balance, I had this checked since the feel of some of what is going on is very similar to throwing a weight or some sort of tire problem, tho the fact that it comes and goes and speed does not change the problem are not normal aspects for this.
-CV Axles & Joints feel good
-Wheel bearings feel good when rotating by hand
-Tire pressures are good and I have varied, running a bit high and low and issue persists.
-While acting up, I put the car in neutral and let it coast and the problem did not go away or change.

I appreciate any help or ideas you have. I am hoping someone has gone through exactly this and has a solution.

Thank you,
Chris
 

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Jack up each lower control arm - putting the jack as close to the lower ballpoint as you can get and THEN shake the wheel that is off the ground --- violently --- and in all directions.
Up.​
Down.​
Left.​
Right.​
Axially.​
Tangentially.​
Radially.​
Rotationally.​
Laterally.​
Off Axis.​

I bet you find it that way.
 

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Okay .... that's bad news .... I thought this would be not only easy but obvious too.

So, let's assume something worse and much more expensive ... <jk ... trying to scare you > ....

SOMEthing is setting up a harmonic somewhere. There's a lot of things that go bump in the night ......

  • Bad CV joint that's undetectable until it gets to a speed or frequency that causes a feedback ... remember that you said it transmits through the steering wheel. We have to assume it's in the front steering/running/power transmission stuff.
  • A bad differential spool bearing. This is sometimes called a "carrier bearing" and if you engage 4High, it might become more obvious. Mebee.
  • A bad pinion u-joint.
  • A bad transfer case output bearing
  • An out of balance front d-shaft (I'm on shakey ground with this assessment..... )
I'm assuming that somewhere or somehow, the drive axle slider is engaged for the next parts ...
  1. The front drive axles are engaged all the time and things are old/loose/worn out from constant rotation even though the 2H/4H/A4W/4L says otherwise.
  2. I need an epiphany here for more ideas.
Do you see that I've kinda shotgunned the front rotating parts here? If I've missed something, I'm sure I'll be scolded ... but it'll be for you and your problem ... so I'll take one for The Gipper today.
 

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Discussion Starter · #9 ·
OK --- what's happening here? Any news?

Is it a boy or girl? Or both?
Trouble shooting and reporting back is a slow process when it can take weeks of driving or a couple 300 mile drives for it to act up. It is difficult to say what fixed it if it does not act up since changing and doing nothing sometimes gets me hundreds to a thousand miles of problem free driving. Because of that, it is very difficult to say if what I change helped, or if the car is just in its everything is okay period again.

I have read on a couple other threads that it could also be the wheel speed sensors acting up due to corrosion. I need to inspect these, unplug, clean, remove and clean if that is possible, etc. I suppose.

I've also thought about turning off traction control (the button on the shifter) next time this happens to see if that changes anything. I have never thought about trying that yet.

Also, if it is a wheel speed sensor thinking a wheel is not turning right, and the cars computers are trying to account for that, I am shocked it does not turn off my cruise control, since this has happened with cruise on.

Ravalli, in your post #4, there are various possible problems, that I do not think fit in with what is happening. Yes I feel it in the steering wheel, but not always. Sometimes the steering wheel is smooth and the rest of the car is shaking and the rear of the car is shaking. Also, it comes and goes randomly with no speed associated with it. I would think if something is out of balance, it would always be at XYZ speed...

I appreciate the help! As people see this thread and have suggestions, let me know and I will keep checking and trying things and report back.

Thank you for the help!
 

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Discussion Starter · #10 ·
Update:
No good news, just more details.

When this is acting up (steering wheel shake and vibration), applying the brakes makes it far more severe. Also, shutting off traction control does not change anything.
 
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