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Discussion Starter · #1 · (Edited)
Hey guys. I wanted to get all your opinions on what could cause vibration in the floor and passenger seat.
It happens with two sets of wheels and tires, including brand new tires.

When the car is on the lift without the rear wheels on and I take it up to 80 mph, there is no vibration.
With the wheels on the car starts to shake around 45 mph. The driveshaft is new and was replaced at 60k.

There doesn't seem to be any vibration at the differential. If you put your hand on the differential while the car is on the rack spinning its wheels, it doesn't vibrate.

What could be the problem?

Paul
 

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you cant check a vibration like that with the wheels on. if you're going to leave the wheels on and run the car on a lift you have to load the rear suspension, put a stand under each trailing arm.
 

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Best way to analyze and resolve vibrations is with a reed tachometer.

Staionary, Hand-held and Dwarf Vibrating Reed Tachometers (Standco) :: Sticht Test and Measurment Equipment

Not sure if you can easily rent one, however, they are available. You might even be able to find a used one on ebay or Craigslist?

Once you can find the frequency, you can then do some basic math to determine the speed of the rotating part that may be contributing to your vibration problem.

Usually driveline vibrations also show up in the rear view mirror, at their worst point, the mirror will vibrate and the view will be blurry out the rear window.
 

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When I had this issue, it turned out my tire air pressure was off. Inflated to the proper level and it went away.
 
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