Chrysler Repair: caravan shaking frontend under power, chrysler town and country, cv joints

Question
Roland,

I have a 98 Chrysler Town and Country with the same problem.  Did you ever here what the resolution was.

Thanks, Jim Anderson




Question
Ihave a 96 caravan and the front shakes from 45 to 55 mph under power only let off and it goes away.I did all the tires new and balanced and brakes had a front end alinment and it's still there.Could it be struts? or maybe the cv joints they don't make any noise.In the mean time we just call the van old shaky.Thanks Keith

Answer
Hello Keith,
One possibility worth checking is the motor mounts. If the rubber begins to fail it will cause excessive vibration when the engine torque is increased. You can get some idea by setting the parking brake, then with the engine running have a helper shift from neutal to reverse and neutral to drive while you observe the motion of the engine. It should be quite secure and if not it would suggest one or more of the three mounts is worn out.
The other general area is the operation of the engine. A routine check for fault codes may give a hint for poor performance at road speeds. It may be possible for you to ask the engine controller whether it has observed any failures in the control systems that are stored as codes in its memory. The most useful thing to do would be to try to get the fault codes that may stored in the engine controller memory to readout. Try using the ignition key: turn it "on-off-on-off-on" and leave it "on" (doing this quickly, no longer than 5 seconds). By "on" I mean just the normal position when the engine is running, not the cranking position. The 'check engine'light will remain 'on' when you leave the key in the "on" position with the engine still not running. But then watch the 'check engine' light to begin flashing, then pause, flashing, pause, etc. Count the number of flashes before each pause and keep track of the numbers. Repeat the readout and verify the counts are correct. Then group them in pairs in the order that they came out, thus forming two digit numbers. You may notice that the pause is shorter between the digits of a given number, and longer between the numbers themselves. Then send me a 'follow-up' question telling me the results of your readout. By the way, 55 will be the last number (two groups of 5 flashes each) and that is the code for "end of readout".
I have the troubleshooting manual for several engines and we can look up the possibilities of what is wrong based upon what fault codes you show. When you write back tell me what engine and model of Chrysler you are driving.
There is also an essay on fault codes at the site:
http://www.allpar.com/fix/codes.html
which gives the meaning of the code numbers. But then you need to get specific info for what exactly might be the diagnostic tests or parts to replace to complete the repair. If this approach doesn't produce fault codes at all, not even a 55, then you will have to go to a good tune-up shop where they have a more sophisticated code reader in order see if there are any codes. You should be able to get a readout for under $50.
So those are some ideas for you to consider. Let me know what happens and how I might be of help.
Roland  

Answer
Hi Jim,
I just wrote to Keith to see if he had solved the problem and if so how, so I'll let you know what he says back.
The other two possibilities beyond my response to Keith are 1)that the engine position laterally in the vehicle may not be centered and that 2) one or both of the front tires have too much radial runout variability. The first one is assessed by measuring the exact length of both drive shafts and comparing them to a spec given in the manual. If they aren't in the proper spec length, then the engine mounts are adjusted to bring them into spec. An alignment shop would have the specs, or the dealer. My '93 manual has the specs for the 2.5L, 3.0L and 3.5L engines, and the measurement is taken between the inboard edge of the outer cv-boot and the outboard edge of the inner boot. If one axle is stretched and the other one compressed beyond the spec then the engine can be shifted via the mounts to balance off the position. The second one is done by measuring the radial variability of each tire surface from the axis of rotation It should be less that 0.04" at the middle of the tread. If it is greater, then you successively try to remount the tire on the rim to reduce the variability to within the spec. That too can be done at a tire store/alignnebt center. Both of those possibilities are associated with vibration in the range of 45-65 mph.
Roland