shudders on the highway

I have a 2002 Chrysler Concorde LXI with a 3.5L V6. When I'm on the
highway (between 55 and 70mph) the car will occasionally shudder.
Usually, it's very subtle and slight, but about twice on any 20 mile
trip, it will be very noticeable.
This seems to happen either with or without the cruise control on.
I have not noticed this at speeds below 55.
I do not notice any hesitation when accelerating or when changing
gears.

If anybody has a good idea what may be causing this problem, please,
let me know.

Thanks,
PaulH

 

Check all engine mounts to make sure they are solid, not oil soaked or
broken.

Have all wheels checked in a wheel balancer, you may have thrown a
weight. They need to check for a busted belt in a tire as well. (will
show up as a lump in the tire) You may also have run into a curb and
bent a rim. That should show in a balancer if the tech knows what he's
doing.

Check all wheel bearings for side-play

Check car for alignment/check for tie rod loosness, both inner and outer.

Check to see that no part of the frame is cracked. (what there is
of a frame, of course)

And this is the tricky one:

Have the engine/transaxle checked for proper alignment -in-the-engine-bay-.

The obvious question - has the car ever been in a collision? If it HAS
been in a collision then they may not have straightened it back out
properly.

Ted

 

No, the car has never been in an accident.

I check (and had checked) all of those items you mentioned. Nothing
seemed to be wrong with those.

Any other ideas?

Thanks,
Paul

 

Yes, one but you won't like it. Put the car in a frame rack and have
the frame checked for straightness.

When you have a resonance shudder like this, you have only 3
areas it can be in:

1) The drivetrain, ie: drivelines/axles, transmission.

2) The suspension, alignment & wheels & tires

3) The frame/unibody


You know it's not in the engine because in your lower gears your
hitting the same RPM that the car hits in the top gear where the
resonance shudder is and your getting no shudder.

And while it could be in the transmission, it's very unlikely since the
transmission parts that spin at the output RPM that this shudder occurs in,
don't have a lot of mass in the drivetrain.

Now, you are positive that it's not the suspension. Your positive that
it's not the wheels or tires. And your positive it's not the alignment.

Thus, the only logical answer is that the car frame is bent.

I personally think that it's in the drivetrain, such as wheels & tires
or a bad bearing in the axles. Despite your claim that you checked
it, my gut feel is that you missed something.

Ted

 

This post looks old but if you have not found a solution I suggest the
inner tie rods. These are a bear to get to and expensive to have done.
It is hard to see if they are bad because the cover plate hides the
ends. It solved my problem which sounds a lot like yours.