[89fiveliter]

It vibrates on the floor when i get to 65-70mph and it vibrates the whole car in a rotating sound. Its not constant loud vibration in one sequence, it gets real bad every second and quiets up a little bit then it gets bad and so forth. I will put it neutral and it gets worse. Then if i put it in fifth it quiets it up a little. I replaced the harmonic balancer and trans mount. Is that the u-joints? Or could my drive shaft be bad? Trans even? Ive only had the car for 2 weeks so i don't know the details of its history unfortunately. Any help would be greatly appreciated! Thanks, Blaine

[7upstang91]

Check the drive shaft for any dents?

[MahFiVeOh]

I had a bad vibration and it was a bad u-joint.There wasn't much "play" in it either and it made it vibrate quite a bit.

[stanGRR]

check your tires and balancing

[2000xp8]

Since it happens in neutral while at speed, you can pretty much eliminate the trans forward.

It's probably the U joints as stated already.
It could be the tires like stangrr stated, but that feeling is usually a wobble of the entire car.

If you have the money, get the ford racing aluminum driveshaft, you car will have never felt as smooth.

[89fiveliter]

U joints it is! got a pair of good ol Autozone gold u joints, 1 hour later it was driving as smooth as a mustang should. Thanks for all the help, it was greatly appreciated. Now on to the low end miss!!! Car runs ok but sounds fluttery down low and on the freeway. It seems to be at 2000rpm and under. I replaced all the plugs, plug wires, cap and rotor......and still nothing! Its really annoying and it runs fine when i get on it. just lugging it around is when i can tell the power loss






89 GT Mac longtubes, O/R H-pipe, BBK Throttlebody, Pulleys, and 3:73's.