A tire not properly balanced. ------------------------------------ Are you car wheels all balanced properly? If not, an out of balance wheel can start to vibrate at certain speeds.
Usually seems to be at about 45 mph
Tires need balancing? Bad C/V joint on axle?
replacing mounts on 1994 dodge caravan
Can you elaborate a little? How do you know it's the transmission? Describe the vibration. Is it only at 45 mph? Does it vibrate when you let off the accelerator?
bad u-joints
The first thing I would check is for broken motor mounts. This causes the vibration around 40-45 mph. There is a service / recall bulletin about this at Kia.
Tires
Around 45 mph.
Around 380
bad u-joint on your vehicleor a wheel balancebut i would look at u-joints first
45 mph is equal to approximately 72.42 kph.
The top speed was around 45 mph. Cruising speed was 35 to 40 mph.