Oldsmobile/Buick Repair: Vibration, vibration problem, chevy k1500

Question
Hi Van,

I was searching for an answer for a vibration problem with my 99 Chevy K1500 4WD and came across Steven's question and your response on 12/23/06. I have over 105K miles on my truck and it just started doing this. The difference is, when the truck gets up to 70, I don't feel the vibration in the steering wheel. It appears to be coming from under my seat. As I look out the driver side window, I notice the side mirror vibrates. I can tell you that there is no or very little vibration at 60. I'll have to see what happens at 80 to see if the vibration smooths out at all.

Do you have any additional information about this? Whatever info you can provide will be a big help. I'll have to provide it to a mechanic since I know nothing about cars/truck.

Thank you for your time.

Sincerely,

-Mark

Answer
Normally....not always, though, but normally a vibration that starts at a certain speed is tire/wheel balance related.
tires coming apart internally can also do it.
A bent drive shaft or bad universal joint can cause it.

The fact that you don't feel it in the steering wheel almost eliminates the front wheels, but not the rear, and not 100% on the front even.

Other driveline parts could also do it, like the flywheel or torque converter, or even inside the transmission.

A fan belt driven accessory with a bent pulley can also do it. That can be tested by operating the engine at about the same RPM as when traveling at 70, but in neutral and sitting still.

Van