FAQ-48

Vibrations: Engine or Suspension

I can't possible guess what your vibration is unless I could ride in your car and hear the vibration. It's kind of like asking me to guess what musical instrument you are playing and not let me hear it. A tech needs to ride in the car to find and fix a vibration, but here are a few questions you can plan on answering to help guide him or her.

1. When did it start, was it after a repair?

2. Is it vehicle speed or engine speed related? Otherwise, does the vibration get worse the faster the car goes of the faster the engine goes? (tires, wheels, converter, driveshaft)

3. What happens when you go 65 mph, is the vibration there? What happens if you put the transmission in neutral, is the vibration still there? (with or without the torque converter applied)

4. If you change the tire inflation to 25 and test drive it, then change the tire inflation to 35, does that change the vibration? (Tire related)

5. Do you see the vibration or feel it? Do you see it in the rearview mirror or feel it in the steering wheel (front end) do you fell it in the seat of your pants (rear of car)?

6. When is it there? Only on acceleration? Only on deceleration? Only on even throttle? Or all the time? (Drive axle problems)

7. Can you hear it? Is it a yayayaya sound? (Scalloped tires) Is it a whine? (Gear noise)

8. When you swerve back and forth, does the noise change? (Bad wheel bearings)

9. Is it present in all forward gears or not? (Trans problems)

10. Has it gotten worse since it started?

11. Does it happen all the time and if not what can you do to make it happen? Is it temperature related? Is it air conditioning related?

Often times, yanking all the fan belts off the engine, then driving it a short distance will help determine if the vibration is a belt driven accessory or not. Last, if it can be duplicated in the bay, these kind of vibrations are often found by touching and moving things until the vibrations changes, then you know you are on the right track.

Just a week ago, a customer came in with a bad engine speed related vibration. You could feel it and hear it at 2100 rpms. Using his hands, the tech felt his way around the running engine and found the vibration on the a/c lines matched what he was hearing and feeling. He found the a/c hoses had rubbed through the insulation where they attached to the fender and were carrying all the engine vibration to the cab of the van. He opened the clamp, wrapped both a/c lines with split pieces of heater hose and the van was as quiet as a mouse. The key here to a quick successful repair was the customers ability to describe in detail the humming noise that he heard and felt all over the van at 2100 rpms.

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