Do any of you have personal experience with the type of vibration I am experiencing? The vibration is about a 4-8Hz vibration that cycles at about a 0.5 Hz rate. That is,it increases in intensity and then subsides, and takes about 2 seconds to repeat. As far as I can tell, it is associated with road speed and not engine speed, although I wouldn't rule out anything at this point.
I have replaced the ujoints. Then, coincidentally, I have a fairly severe vibration that was engine related. The harmonic balancer developed a crack in the keyway. It spread the hub enough to start a wobble and slipped over the key and the balancer was about 1/3 out of time with the engine. I replaced the balancer and cured that vibration. The cyclical vibe is still there. I also replaced the tires. The old ones had been on there quite a while and were starting to dry rot, had a couple of small bulges on the side, etc. They needed changed anyway. I also have ordered a new crank pulley and
trans mount (see next paragraph for explanation). I'll change those this weekend.
My ideas about what it might be: 1) crank pulley has a slight wobble in it. If I view it from the side at idle I can see that it isn't concentric. Maybe damage from the HB failure. Makes the AC belt flop a little at speed. 2)
Trans mount. Someone told me that was common. It's cheap enough to try it. 3) Driveshaft balance. Could be damaged in some way??? Bent???
What I'm looking for is someone who has had a personal experience with a vibration like this, and what they may have done to fix it. I will welcome all fresh ideas.
Thanks,
Mike
Tough-to-find cyclical vibration 
