Bad vibration above 1900

Bad vibration above 1900


Full Time Jeeper
Cincinnati, Ohio
1985 jeep cj7 360 20 rear and 30 front w/warn lockers 5 speed tranny,

1971 dodge dart built 318
I have a vibration that gets severe enough that I can't take it over 2000 rpms. I just replaced the vibration damper and it still does it. The replaced one was in bad shape. Now I have a minor knocking noise. I have bull tare pulley kit that is not on yet. Wtf could be causing this
Motor or trans mounts???
I think it may have to do with the knocking noise
Motor mounts can cause this bad a vibration? Could it be pulleys? Could it be internal? What would a damaged crank act like?
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Sorry to double post. I think my next suspect spot is the flywheel for the man transmission.this is an engine swap from po. To a 360. The plate is missing, I'll bet a 304 is on there. How do I trouble shoot this. Any way of checking the flywheel?
Not sure how you would be able to tell from the outside without removing it.

Id first check to see if they even differ. Its quite possible that they are the same.

If they are different, Id find a way to look at both (find a parts store that will get both there for you) and see if they differ visually. Then compare through the clutch fork dust cover or starter hole.
I am planning a rebuild, just not yet. This may be the forcing factor. Would anyone have an idea of how much a rebuild would cost me? The block and heads are stock.
did this just start?? I do not think that a 304 flywheel will even fit on a 360 but I will not swear to it. I am standing here waiting to be corrected.

But a different 360 flywheel that is not balanced for the engine will fit. I think there are a lot of doaner 360s from waggys with positrack.

If it was the flywheel it would not just start vibrating unless you threw a bolt from the crank or the clutch.:eek:
No, not new issue. It just cannot go above 2000 without vibrating uncomfortably. Should I put the pulleys on and see? I just do not know how to trouble shoot this.
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AMC V8's are externally balanced. They MUST have the correct balancer and flexplate/flywheel!! They are dimensionally the same and will bolt on in place of one another but the balancing weight differs. If it is a 304 flywheel on a 360 it needs to be removed and re-balanced to 360 specs or it needs to be replaced with a 360 flywheel BEFORE YOU RUN THE ENGINE AGAIN. Maybe you can save the engine but as one harmonic balancer has already died trying to stop the unbalanced engine's vibrations I do not have high hopes for it. Best of luck.
Ok, thanks for the response. Would a rebuild and check rotating assembly do it?
Generally such a vibration is hardest on the crank bearings. That may well be your knocking sound. A basic rebuild or even just a crank kit would correct this if that is the case... maybe you will get lucky though.
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what he said^^

first, I would be looking for a 360 flywheel or at least confirm that I had one. I would not be hopeful about being able to balance a 304 flywheel to a 360. It has something to do with the counter weights not being in the same position?

Question: does the V8 flywheel have a dowel pin in it to allow mounting in just one position?? Perhaps the flywheel is out of "time"??
i think pulling the belts is a good idea. I had a pretty bad vibration once due to a bent fan; finally broke itself off.

Could you explain how this started again?

This was happening from the time you bought the jeep? Did the PO mention this or can you contact him?

As far as the you already replaced a known good one with another good one, and it failed?

I would def. diagnose the problem before jumping into a rebuild. It may be something simple. As far as the knock goes; don't condemn the engine yet. You may be hearing something else.

Or you might have thrown a rod bearing and thats the noise and vibration.

Pull all the belts and see what that does.

You can also get an idea of what each cylinder is doing by pulling one plug wire at a time at idle. If the knock goes away while one of the wires is off, thats generally an indication of a problem with that cylinder. Usually a rod bearing.

You can also either use the oil off the dipstick or drain the oil and check for bearing material.
As was already said, the 304, 360, 390, 401 do not share the same flywheel. They will all bolt to each engine, but they are balanced to a different spec.

If you are getting a vibration between 1500-2000rpm that isnt allowing you past that range, I would strongly suspect the wrong flywheel. This happens more often then you can imagine as people replace flexplates from auto equiped V8's with standard transmission flywheels.

Yes, it will tear up your main bearings and start on the journals.
Thanks all! I will swap belts and check the flywheel. I just have a feeling that's what it is. I just dug into her this past weekend after the winter down time. I'll get in there this week and let y'all know. I really appreciate the help!
Ok, I have more info. This vibration rattles the vehicle at startup, as I let the clutch out. It has a high vibration below around 1500. Past 2 grand is a no go. :dung: would rattle to pieces.. The idle has a surge under the hood and a little chop at idle. I have been reading, could my problem be misfiring? How do I test the cylinders? I can check the compression in each, but how do I know if all are getting compression how to tell if they are all firing? If I check spark, how do I know it's not lean misfiring?

Thanks in advance!
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All Good suggestions , maybe the Flywheel could even be the clutch or pressure plate or for that matter the drive line. You might dry jacking the vehicle up on all fours with jack stands and run the motor and shift through a few gears.
You have not yet been clear when this all started? Did you just buy the vehicle?
Been going on since I bought it. Po has no idea.
Been going on since I bought it. Po has no idea.

Question: "Clutch in" does it vibrate when you bring the motor up in RPM?
If it does its in the motor,flywheel or clutch.motor mounts.
If it does not its in the drive train.:)

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