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Wednesday, October 01, 2008

I noticed a vibrating sensation that runs through all of the car

QUESTION: Dear Sir, I own a 2006 Trailblazer, it is only 46000 KM. Recently I noticed a vibrating sensation that runs through all of the car. It is most intense when cold and decreases after running the engine for a while, even when driving it is there but with lower intensity. I can feel it much clearer when I start the engine apply the brakes and shift the automatic transmission to "D" and try to take off while still applying the brakes. The vibration max is at 1200 RPM. Please advise ANSWER: This could be real easy or could end up being a real pain to find. GM has issued a couple of bulletins regarding this kind of a problem from different components in the chassis and drive line, etc. It makes a difference if the truck will do it on a hoist in the air or not. Some of the more typical things to look for would be bent, loose or missing or miss aligned exhaust components that are grounding out. If you can power brake the truck and make it do the vibration while someone else walks around it with a pry bar, you may find it. Have him apply pressure in different directions to things like the exhaust system. The rear transmission mounts, cross members, etc. Just about anything that can move or is mounted in a rubber bushing should be suspect. According to GM, you should even go so far as to check the drive line angle to be sure there is no harmonic resonance coming from the drive shaft. Some of the earlier ones had to have a vibration dampener added to them to stop the harmonic vibration from them. Even loose steel fuel or brake lines flexing against the floor board or frame could set off this kind of noise or vibration, as could an out of balance or lose fly wheel or flex plate on the rear of the motor, if it happened to be loose or had thrown a balance weight off of it. This gives you a few ideas, unfortunately, it can't just automatically be pinned down to any one component as there are so many possibilities. Including mounting brackets under the hood. But GM also has what is known as a chassis ear that can be attached to various parts of the frame and body and then have the car driven to help narrow down the area or cause based on the harmonics of the vibration, you may end up needing to use that kind of a tool to find the problem.

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