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Discussion Starter · #1 ·
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
 

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The vibration which you state is at a low frequency which leads me to think that there may still be a problem with the tires or wheels. Have you checked for wheel run out? In other words a bent wheel.

Tires, even if new, may be out of round, but since the vib. was there before, it may be balance. Wide wheels/tires actually need to be balanced on the front and back sides. The balancing machine that was used may not be properly calibrated or is not capable of balancing your tire/wheel combo. Some people don't like to see balancing weights on the front side of the wheel because it doesn't look good, but those weights may be necessary.

If the tire shop that you use doesn't have an up to date balancer, find a shop that specializes in mounting wide wheels/tires. Get the tires rebalanced, if the vib. is still there, check for run out. It may be best if you do go to another shop for balancing in case there is a problem with your original shop's balancer.

It seems to me that a drive shaft or engine pulley problem would produce a higher frequency vib. which is determined by the rotational speed of the component. A driveshaft spins faster than the wheels as would the pulley and a higher freq. vibe results.

One thing that you may want to check is the front wheel bearing nuts to see if they are torqued to spec. If the bearings are loose, a run out problem may exist there. You also want to torque down the wheel lug nuts with a torque wrench. Uneven torque on the nuts may distort the wheels. Tire shops love to go wild with their impact wrenches and it's anybody's guess how tight the lug nuts will be. Usually they're way too tight.

Even if you're not using wide tires and wheels, getting the tires balanced at another shop with an up to date balancer will eliminate any doubts about balance. You will still want to check the wheel bearings and lug nut torque. If you find that you have to check for wheel run out, a check of the axle flanges may be a good idea. A bent axle may be found.
 

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Along with Greeks comments, you might also want to check that the back of the rim is seated on the brake drum or disc. I've seen wheels that are not seated properly, ie the lug nuts are tight, but the wheels are not seated and produce a vibration.
 

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Discussion Starter · #5 ·
I accidentally posted this twice. In the other post Jay67fast had the same thing on his car and said to change the tranny mount. I had several people tell me the smae thing. Never would have believed it, but they were right. Changed it last night. Smooth as silk, or at least as smooth as a 40 year old car ought to be. Not quite like a new car, but what fun would that be??
MIke
 
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