Here is a chart that comes in handy.
http://www.armorb.procarcare.com/inc...04/4fig15.html

 

I had the same issue in my 70 coupe. It started about 30MPH and went away at about 40MPH. It was only on acceleration so if I let off the gas it smoothed out. I had the driveline rebuilt with new U-joints and balanced. This solved the problem.

 

my explorer did it bad at 30 as well. I just put a steering stabilizer on it and it drives like a new car. Course I have it liftedwith over sized tires so that doesn't help too much.

 

Let us know what the cure is.

 

All right so i narrow it down, is not the gears, beacuse i recently put a new differential and it had the vibration before that, it has new suspension, recently aligned, tires balanced, wheel and axel bearings replaced.

I dicovered today that i had the same vibrationat about 3000 RMP with the car not moving on PARK.


Please i need some help to determine this problem!

 

One more question,
I noticed in Mustang plus there are 2 different sixes of U Joints, 3 1/2 or 3 7/8 how do iknow the correct size, i have a stock C4tranny on my 67 mustang coupe

 

Please i need some help with this problem, what can it be if i feel the same Vibration, @ 3000 RPM on with the car not moving onPARK...

Thanks

 

harmonic balancer, flywheel or torque converter out of balance - my bet on the torque converter if you feel it thru the seat.
broken engine mount (unlikely)

 

Broken motor mount???

 

I just replaced the Motor Mounts,

How can i check for the Torque converter?