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Discussion Starter #1
I swapped my old and tired 302 for a Levy 347. I also replaced the engine and tranny mount for new ones. I have a vibration that starts at around 60 mph and I cannot find the source. Pinion angle should be a suspect but since I did not change anything in the geometry I am trying to identify other suspects...any ideas?
 

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Not a waxer
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Road speed dependent or engine speed dependent? In other words do you get the vibration at the same 60 MPH engine RPM when parked? If the answer is no then you better revisit the pinion angle since the geometry may have changed somewhat with the different engine and trans mounts.

Jeff
 

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Official OLD GUY
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One thought that crossed my [single celled] mind, did you reuse the old flywheel from the 302 on your new 347? 302 would have a 50 oz balance weight, most 347's are being built with the older 28 oz balance weight - definitely a cause of a vibration as your new engine would be out of balance. Usually shows its ugly head around 2500 rpm; about the engine speed at 60 mph if you are using the normal gearing most of us use . . .

I have a close friend that is going thru this very issue for the reason I mentioned right now

Just a thought.

Doc
 

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Discussion Starter #4
It is really speed dependent not RPM
 

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I'd be checking that pinion angle again.
 

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Discussion Starter #6 (Edited)
I'd be checking that pinion angle again.
I checked it and it doesn't look right: my tranny is 1 deg down the diff is 1 deg up and my driveshaft is 5 deg down, since I've got a 4 link the only option would be to raise the tranny but my driveshaft angle is already too much...
 

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Pro FFR Builder and Moderator
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Call me
 

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Discussion Starter #8
Gordon, I do not think it has something to do with the engine, it still vibrates with the clutch depressed at 60mph!
 

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FFCobra Master Craftsman
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Do you feel it in the steering wheel or seat. Steering wheel is front and the seat is rear. I would remove the driveshaft and turn it on hole and reinstall.
 

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Discussion Starter #10
Definitely rear, I will remove the driveshaft and inspect.
 

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I has a similar problem after swapping engines, stock 302 for a Dart block. Turned out I needed to adjust the pinion but also had the u jount binding, took a grinder and opened it up a little bit. I could see where the u joint was binding by the wear on the paint.
 

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Discussion Starter #12
Just checked the drive shaft and found nothing wrong
 

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Snake Farmer
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Driveshaft out of balance? Any new dings, dents or weights missing?
When you swapped the engine, did you pull the tranny or leave it in?
 

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Discussion Starter #14
The tranny went out with the engine
 

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Adjust the rear to make the driveshaft more in-line with the rear while on jackstands. If the tires are off and you look from the side, you can see the driveshaft U joint angles. You only need 1 degree at most down on the pumpkin anyway. My guess is the trans tiled up a hair, your rear is pointed down quite a bit, maybe a few degrees. So, the driveshaft is binding now.
From my own experience, the driveshaft binds very easy. It doesn't have to be out very much (it is so short). I remember swapping one of the 6 engines I have had in the car, it vibrated like hell. I put a less downward tilt on the rear and it was perfect. A friend of mine raced cobras with me. He decided to install a Jerico, didn't check the driveshaft angle. He snapped his driveshaft at CMP.
 

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Discussion Starter #17
Thanks trevor that makes sense, I need to figure out a way to bring the tranny down...
 

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Discussion Starter #18
Just ordered a C4 tranny mount which is supposed to be half inch lower...we'll see!
 

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I had the same problem after going from 302 to a 347 with 28oz flywheel. It vibrated at 60mph in 3rd gear - and 3rd gear only. Pinion angle was OK. I had a 4-link and I bolted back on that UGE dampener from the Mustang. That solved the problem. (I later went to a Levy Racing 5-link)

You said you had 4-link, curious - are you using the dampener?
 

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Discussion Starter #20
The dampener...I ditched it 15 years ago!!
 
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