Resonating vibration

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oldirish

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I have a 72 Duster 360 magnum with a 518a transmission. It's just been put together and there is a vibration when parked and I accelerate and when driving around 2000 to rpm. I've read about the crank vibration damper and the magnum flex plate.

I'm attaching pictures of what's on the car.

There is no scallop or drilled holes on the flex plate that I can see.

Any help is appreciated.

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No weights on the converter? Hard to tell about the balancer since it's installed and aftermarket. Unless it has a weight bolted to the back of it, it's the wrong balancer. Unless there's a weight on the converter, it may be wrong, too. Probably put together by someone who doesn't know Mopars.
 
That's an LA flexplate- very wrong for a 5.9 Magnum, and who knows what kind of aftermarket balancer.
Is this a stock 5.9 shortblock, a stroker, or what? Was it rebalanced during a rebuild? Unless it was, you got the wrong mishmash of parts for a Magnum.
Time to figure out what you've got before the motor eats itself.
 
Great info and exactly what I was looking for. Any recommendations on a flex plate and balancer, this isn't a race or show car, I plan on driving it.
 
oldirish said:
Great info and exactly what I was looking for. Any recommendations on a flex plate and balancer, this isn't a race or show car, I plan on driving it.
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Can't make any recommendations until you answer the previous questions-
Is this a stock 5.9 bottom end, or a stroker, and was it rebalanced during a previous rebuild?
And, if it was rebalanced, to what specs? Neutral balance or external balance?
 
Damper looks like the Summit SFI unit, they come with weights for 360 LA and 5.9 Magnum and there should be one bolted on the back side.

Factory 5.9 Magnum flex plate will work.

All that said, those parts will only work if it has stock rotating assembly, or was balanced to factory 5.9 Magnum external balance specs.
 
This is what I know, I bought the Duster with the engine/ transmission out of the car.

The heads on the engine were built at a machine shop in Albany Ga where I bought the car.

I don't have any specs on the engine. I was told that it had a mild Comp cam in it.

Once the car was assembled it cranked right up, had a little valve clatter but that is mostly gone.

It has the Sniper2 EFI and Hyperspark ignition.

I believe all 360 magnums are externally balanced from the factory so I'm going to be checking the damper and flex plates to start.

I'm also going to have the sniper checked out because I've read some comments about it causing vibration.

I'm fairly certain it's engine related since it vibrates in neutral at idle and higher rpm's
 
MopaR&D said:
Damper looks like the Summit SFI unit, they come with weights for 360 LA and 5.9 Magnum and there should be one bolted on the back side.

Factory 5.9 Magnum flex plate will work.

All that said, those parts will only work if it has stock rotating assembly, or was balanced to factory 5.9 Magnum external balance specs.
Click to expand...
Are the 360LA and Magnum dampers the same? I thought some 360LA's were internally balanced?
 
oldirish said:
Are the 360LA and Magnum dampers the same? I thought some 360LA's were internally balanced?
Click to expand...

No, the 360 LA uses more offset weight as the stock LA pistons are heavier than the Magnum pistons. All 360 Mopar engines whether LA or Magnum were externally balanced from the factory.

All other SBM engines (273, 318, 340) were internally balanced except for the 1973 340 engines that had cast crankshafts.
 
oldirish said:
This is what I know, I bought the Duster with the engine/ transmission out of the car.

The heads on the engine were built at a machine shop in Albany Ga where I bought the car.

I don't have any specs on the engine. I was told that it had a mild Comp cam in it.

Once the car was assembled it cranked right up, had a little valve clatter but that is mostly gone.

It has the Sniper2 EFI and Hyperspark ignition.

I believe all 360 magnums are externally balanced from the factory so I'm going to be checking the damper and flex plates to start.

I'm also going to have the sniper checked out because I've read some comments about it causing vibration.

I'm fairly certain it's engine related since it vibrates in neutral at idle and higher rpm's
Click to expand...
So, are you saying it's 5.9 with a stock bottom end, no mods?
If so, put a stock 5.9 Magnum flex plate in it, make sure the aftermarket balancer has the 5.9 weight on it, and you should be good to go.
And no, Magnum and LA 360s are completely different, although both are externally balanced it is still a different balance. The dampers do NOT interchange.
 
5.9 Magnums are externally balanced. 5.2 Magnums are neutrally balanced. I use the latter when I run a neutrally balanced Magnum bottom end. As mentioned, it requires one mounting hole to be oblonged.

200R4 3 (Large).jpg
 
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