Go the same rpm in a lower gear and see what it does.


If someone can supply the gear ratios for your transmission, we can figure out what the speed will be in lower gears.......

_________________
Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

After reading additional posts past my earlier post I think you have a dry U joint that is in early stages of failure.

My Dart always had a seat of the pants vibration that seamed to come and go but always at speeds over 60 mph. This irritating condition keep me from rolling down the road much faster than 60 mph, and I always thought is was an engine balance problem. I did all the stuff you did kicking it out of gear at speed, wondering if wheel baring's were culprit, tire balance... and on it went for four years scratching my head.

I finally changed out both U joints, both of which showed no play when in place; problem solved no more harshness at 60 mph. Your car is geared much higher than the 3.55:1 rear gear I am running so vibration mph speed in your car moves up several notches based on drive shaft rpm.

You car has been sitting for a long time with only 9k on the clock, and its factory grease contained in "lubed for life" suspension and rotating assemblies has most likely degraded and no longer able to do its job properly.

_________________
67' Dart GT Convertible; the old Chrysler Corp.
82' LeBaron Convertible; the new Chrysler Corp
07' 300 C AWD; Now by Fiat, the old new Chrysler LLC

Have you:
1. run a compression test to see if the cylinder pressures are close to equal
2. check the plugs during that process for any oiling or misfiring
3. check or replace spark plugs and wires
4. pull valve and check valves for any sticking (and adjust juuust in case you find that this was an '81 that somehow got the last of the mechnical lifters)

And I think the info above is spot on: the old grease will be really drying out just about now and will show up in stiff steering action and very possibly the u-joints.