Is this a problem that has been getting worse for awhile or just started all of a sudden? Did it start after something was repaired, or replaced? When you said that u-joints look OK did you just look or did they feel ok? U-Joints can be deceving toanyone that haven't had some experence with them, Usually you can twist them, and you can see the play, other times they may not have any looseness feel stiff. Stiffness in not good, they can become stiff due to dryness, this is the way you get more viberation, the joints have no flexiblity.--- Try this. Put a block in front, and rear of front wheels. Jack up one side of the rear, put a stand under the frame or axel to hold it 4 0r 5 inches off the ground. Start car put it in drive, if jouint are bad you should get a indication, the drive shaft will turn free or it will make noise, and turn rought. From your decription this is probable your problem. When you have your throttle ingaged the force will cause the joint to turn somewhat better than no thorttle, with no load you will get the full force of the bad joint.
Hope this helps.
Good luck
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Tuesday, June 13th, 2006 AT 3:59 PM