[1986 scott]

I am new here and am having a problem with my 86 gt! can you help?
:headscratch:

I have a horrible vibration in the rear end @ about 55-60 MPH. It is coming from right under the rear seat, so I am assuming that it may be the universal joint.?

 

[StangLX93]

most likely its not a u-joint, if that were the case the vibration would not be at a certain MPH but throughout your RPM band, at 50-60MPH i would suggest you inspect the wheel for warpage, and the tire for damage, and see it threw a weight, also you didnt mention if you have aftermarket wheels, reason i ask is i have Weld draglites, the valve screws into the wheel versus others that pull through, the nut on the valve assembly fell off iside the tire and made a huge vibration, well hopefully this helps

 

[EagleAutosports]

I would get under there and check all of the bushings and then the torque box welds. You'd feel a u joint before you got to 55-60 mph.