Menocar

I just bought this 1999 Mustang Convertible, V6 automatic. When I get to 50 MPH a vibration occurs that can be felt through the seats. It's a low frequency rumble that is from 50 to 60 MPH only. You can feel it though your whole body. Also, it only does it under power. As soon as you back off the throttle it disappears. I don't detect any clunking, thinking it was a bad u-joint but I've only driven it 300 miles mostly on the highway. I originally thought it may be tires but when I noticed the pattern of vibration under load, no vibration under no load it got me concerned. I never owned a Mustang before so any feedback/help is greatly appreciated.

AzPete

First of all, I would have the tires balanced and checked for bent rims or separated tires. This would eliminate a common source. If that does not change the vibration, you might try rotating the drive shaft 180* on the mount to the rear end. Easy to do and could change how thing vibrate. Bad u-joints do not always "clunk" either. Do one thing at a time to see what makes a difference.

rygi23

it's definitly the drivetrain but don't think it's u-joints. Probably doing it after the tranny shifts into OD, that's when there's more torque on the drivetrain. Flawed, or loose, engine or transmission mounts are my guess.