Chrysler Repair: 1996 Chrysler T&C LXi, 3.8l?vibration/abs issues, wheel sensors, radial variation

Question
QUESTION: My 1996 Town & Country LXi (3.8l) has developed 2 front end related problems, however, i do not think they are related, but I'm mentioning them here together just in case there is a connection.  If you could help me with either or both, I'd greatly appreciate it. 1) between the speeds of ~37mph to ~43mph the van shakes from "side-to-side" (at least it feels like it is from side-to-side).  I have balanced/rotated all tires 2x.  It only does this at those specific speeds - it appears to me that is also the specific range at which the transmission is shifting gears from ?[2nd to 3rd or 3rd to fourth]?  I put the car on jackstands and ran it in drive and did not notice any significant wobble in the front wheels. I also observed the engine and it seemed to move upwards ever-so-slightly at the time the transmission shifted around ~43mph.  While sitting in the drivers seat, i could still feel the shimmy @ ~43mph even though the van was on jackstands.  2) While driving the vehicle and coming to a stop, the ABS appears to kick in for no apparent reason and actually makes it difficult to stop - sometimes i really have to put a lot of pressure on the brake pedal.  When i remove the ABS fuse, the ABS problem goes away, so i assume it must be ABS-related.  I did not notice anything unusual when i inspected the wheel sensors.  Any suggestions on either/both problems?

ANSWER: Hi Keith,
Sometimes that vibration around those speeds occurs because of either the wheel or the tire (or both and then you have something to 'play' with) are out of round. If you have a dial indicator or similarly try to assess how great is the in and out radial variation of the tread radius. It should be less than 1/16th inch. If it is more, then if the out of roundness of the wheel radius at the bead can be 'matched' to take advantage of any similar out of roundness of the tire you can counteract one against the other in what is called 'match mounting' to reduce the overall out of roundness of the tire/wheel duo.
But because you say that the affect was felt with the wheels off the ground, that possibility is eliminated, and also you said that the tires had been balanced which should also remove that as a source of the vibration.
You might want to assess the condition of the three engine mounts, one of which may be weak. That would allow the drivetrain to move excessively and opens the door to vibrations. Watch to see the amount of movement of the powertrain when you shift from neutral to drive and to reverse. I can't quantify what is excessive play in the mounts but it may be obvious that one of them is allowing to much free-play. Given the age of the vehicle it may well be time to refresh these mounts.
On the ABS you might seek a fault code readout of the ABS controller memory for something that it may have noticed. I believe you should have an OBD-II reader socket under the dash next to the steering column. I fairly sophisticated reader may be needed to access that ABS memory but you could try for a free readout at an Autozone parts store. But ask specifically for the ABS memory to be readout as that is a separate request from a powertrain readout. Diagnosis of ABS issues usually begins that wsy. I have the '95 and '98 manuals (model 4 and model 20 abs systems) so if you can see any lettering on the abs controller which sats which model your '96 has I can xerox copy the pages about these aspects of the system and postal mail them to you.
Roland


---------- FOLLOW-UP ----------

QUESTION: Roland - Thanks for the fast response!  I don't know if this information helps with the disagnosis, but when i took the van for test drive again this afternoon, i noticed it does NOT shimmy when coasting between 35mph to 45 mph - it only shimmies side-to-side when my foot is on the gas pedal and at those speeds.  Also, AutoZone told me they would only read OBD-II Engine codes, NOT ABS codes. :(  I'll see if i can get any codes off the ABS controller when i get a chance.

Answer
That lack of shimmy when coasting reinforces the possibility of a engine mount being worn too much which would only be brought significantly into play when you are applying torque from the engine to the drive axles. If there are no noises (clicking sounds, say from a cv-joint that has lost its grease due to a torn seal) then presumably the drive axles aren't the cause. Given the age, my suspicion is a mount. Did you have a helper shift the trans into reverse and then same to drive with the engine idling and a foot on the brake? That will give you some idea about how much free play there is in the engine mount 'suspension'.
Roland