2001 Taurus bad vibrations

Recently my car began vibrating in a shudder like fashion between 45-60 mph. This action is most severe at 1800-2000 rpm with or without overdrive. At those speeds, easing off the accelerator eliminates the
shudder. Motor mounts are reported to be fine. The front tires have been replaced with no effect. Any ideas are greatly appreciated. Could a simple tune-up fix this problem? (over 35k)--Oscar
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Torque converter out of balance? (for whatever reason)
r/ -IanCT

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[This followup was posted to alt.autos.ford and a copy was sent to the cited author.]
snipped-for-privacy@webtv.net says...

Did you have the back tires checked? Is there any vibration when just parked, but carefully revving the engine to the indicated rpm's? How about in gear, but with the brake applied (only do this for a few seconds or you'll overheat the transmission.) Does it do it at lower speeds/gears, but at the same rpm's? This will help narrow it down to engine or transmission/wheels.
When it does it, try shifting into regular drive instead of overdrive. Does that make a difference? If your transmission has a '2' selection, you can also try that (actually, '1' will work, as it will not drop all the way into first at those speeds.)
There isn't much tuneup you can do on today's engines. I would think a bad spark plug or wire would show up at idle and most all rpm's. If it's bad enough, it would throw a trouble code.
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My car did this too. After balancing and rotating the tires the shudder went away. Also if your front end is out of aliment that can cause it as well.

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Many thanks for responding. I am sched'd tomorrow for round two at the mechanic.
As for the questions posed to me: It appears to be narrowly confined to the stated rpms at the stated speeds. I have carefully observed rpms @ 1800-2000 at lower/higher speeds and higher rpms while accelerating faster thru 45-60. The typical episode goes like this: upon shifting into the higher gear/overdrive(mech's suggestion btw), the rpms naturally drop to 1800 before settling in at 2000 and slightly above. This is accompanied by the stated shudder. Should I relieve pressure upon the accelerator the shudder vanishes. The rpms may drop from 2500 back down to 1800 during this coasting maneuver. Touching the accelerator provokes a strong shudder, clearly felt through my right foot enough to shake my leg. I would describe this shudder as having a low end frequency but high amplitude in the range of motion and rapidly thereof seen in this phenom.
I'm no mechanic but seems to me that tires would provide a constant effect with no relief while coasting, although perhaps the front wheel drive could be involved if the tires were to at fault. While in park, neutral, or idle there is no shudder at any rpm.
Torque converter is something I will ask about to be sure, as to me it almost feels like the exhaust pipes (or something akin to that shape) under the car is wobbling violently. Could that be it I wonder (tc)? I also wonder about the possibility that a motor mount is cracked or fractured in such a way as to be not noticed as yet. I still wonder if a fuel injector could be off enough to cause the engine to go so out of sync as to shake and rattle while I roll on.
I'll let the pros handle the problem but I shall ask if I'm not satisfied with what I hear (or feel).
Thanks again. I'll let y'all know how it goes.-Oscar
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Turns out the passenger cv joint was bad and needed to be replaced, fyi. Runs smoothly now. Many thanks for the interest and suggestions.-oscar
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