I have a 1998 Subaru Legacy Outback wagon. Over the past couple of months I have been noticing a vibration when I am driving up around 55 to 65 mph. It seems to shake the whole car. It does not do it all the time and it comes and goes as you ar driving it. I have slowed down to different slower speeds and it is still felt when it is doing it. I have checked all the suspension and can find no excess movement in any thing. I have check the u joints and can feel no extra in them also I have no clanks when putting it in and out of gear. The only place I have found movement is at the center support bearing. It does not take much force or pressure to get this movement. Can anyone offer me suggestions on what it might be and what to check. And if it is the center support bearing can anyone tell me what I will need to do to remove it and replace it. Thank you for any advice given.

When was the last time that you had your tires ballanced?  If it has been a while you might want to have them checked. 

X2 On the tire ballance. You can wear down a set of tires not doing that for a while as well.

swap front and rear tire pairs and monitor for any changes.

 

also, some folks have had a dragging caliper cause similar issues. maybe use a remote infrared thermometer and compare hub/brake temps side-to-side after a highway run.

I am getting real hot hubs on the rear, both sides. I have backed the adjustment off some on the emergency brake. But still need to get the calipers off and checked. I have checked both sides for play in the bearings and cv joints. Could the rear differential being low on grease cause any of this? I have grabbed hold of cv joint shafts and they do not feel real hot only the hubs do and they are hot enough you cant even really keep your fingers on them. Could it be the bearings? But I do not feel any slop in them.

Although soob bearings can fail in odd ways, both the bad ones I've had would 'rock' up-down (12 oclock to 6 oclock) when lifted off the ground. One of them was very noisy , the other one silent. they both only moved a coupla mm.