When I drive my Chrysler and increase speed the car vibrates, but when the car reaches speed it stops vibrating.My suspicion was the driveshaft center support, but the car has a whole driveshaft (not split).Could it be the universal joint that needs to be replaced (mine is not greeseable)? I didn't feel anything when I wiggled the driveshaft by hand.

 

I wonder if what your feeling is an engine miss under load. Do you feel it as soon as the car pulls away from a stop? What if your already at speed and then hit an incline?

Is there any vibration on deceleration?

If you take the transmission out of gear (or push in the clutch) have any affect? How about varying the engine rpm while doing this?

 

No, it doesn't missfire. The engine runs just fine. the carburettor is newly refurbished. You feel the car shaking when you slowly increase speed. It feels like it vibrates when straining the driveshaft or similar. Thats way I thinking of the universal joint.

 

Is this a new issue that has recently came up or has the car had this issue for awhile?

Are the tires in good condition? No flat spots from sitting? Not more than 6 years old?

Other than that you could double check the driveshaft geometry.

Check driveshaft phasing (easy)
Check Shaft Run out with a dial indicator
pinion angle (not so easy without a drive on lift)

Also, It may be worth looking at the u-joints again. It can sometimes be hard to gauge their condition with the shaft still bolted on the car...

Thats all my best guesses. Perhaps other forum members will chime in soon.

edit: check for missing driveshaft weights

 

I recall this type of problem when I worked at the dealer. Many times, it turned out to be a motor mount, most of the time the rear one/transmission mount. I recall changing one mount and that set the stage for a vibration. Just an FYI

 

yeah, u-joints is my best guess.