74 Dart Vibration

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jorgy84

jorgy84

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In need of help. I know there is a tone of threads on here for a vibration in a 360-727 set up. I have read threw a lot of them check a bunch of stuff and am still failing to find the issue.
So as for what I have done to the car. I updated the drive train to rebuilt 360 with a rebuilt 727 backing it. Motor is supposed to be balanced to factory specs witch call for all the external parts to balance it out.TCI neutral balanced Saturday night special converter, B&M flex plate for the external balanced 360, new balancer for the 360, and all new mounts for the motor and trans. That is how the car is currently set up.
Now for what has been done I've changed out the B&M converter for the TCI because the center hub on the B&M was bottoming out in the crank.
I've checked the flex plate with another brand new one no difference. I've changed out the tranny mount. I changed out the original balancer for brand new aftermarket stock replacement due to a grove where the seal rides.
I've tried running the car with no belts on it.
But this car still has a pretty good vibration at 1500-1800 RPM and it will smooth out as the RPM picks up but never goes away. Doesn't matter if its in park or gear vibration is the same.
Nothing that has been done this far has changed the vibration one bit.
Any and all help is very much appreciated I'm getting tired of banging my head on the wall.
 
Unfortunatly different year 360 engines have different offset balance weight requirements . these must be matched correctly of vibrations will shake the engine to death . I suggest that you double check the amount of weight necessary for your application as modifications may have caused this .
 
Yes the converter is neutrally balanced.

I believe the block is a 70s block. I don't know a year any thing else is.I know the guy who built the motor said I will need all the external balancing a stock LA calls for.
 
I'm not sure what to do in your situation.

When I had the machine work done on my 360 I gave them the crank, harmonic balancer, and the cutout fly wheel for balancing. I had them balance that entire rotating assembly. That way it's compatible with any neutrally balanced converter.

My best guess is talk to the place that built your 360 again and ask what exact parts are they saying you need.
 
Found out the crank is out of a 73. The balancer I put on was a stock replacement for a 74. When I go to summit and look up a balancer for a 73 it only shows one and not either of the ones I have for this motor. Think I need to dig more on that.
 
Waiting on a new balancer hoping it solves the issue. If not the motor will be coming back out. I'll post an update as soon as I get it installed. Thanks for the help so far.
 
Installed the new balancer last night. The vibration is still there. I really don't want to pull the motor. But I don't think I really have an option at this point.
 
After I took my torque converter bolts out I notice 2 mounting pads had a bigger gap than the other 2. So I matched marked all the pads to holes and it's always the same 2 pads that have the larger gap and same 2 with the smaller gap no mater what hole you try to line it up with.
 
Quick update tore the motor down don't like what I see at all. Took the rotating assembly to the machine shop. Just waiting to hear back. He seams pretty confident it isn't balanced right.
 
Update
After rebuilding the motor and actually having the rotating assembly balanced. Plus having other issues with the block fixed. That where never addressed that should of been. It's back together running with no vibrations. Needless to say if I need another motor for this car I'm building it my self.
 
As to what actually cured my motors vibration. Well it was a combination of things. First off the crank was out of balanced. The rods and pistons where not balanced. The line bore was off do to the #3 main cap not lining up right. Those are the things the machine shop addressed that he believed fixed the vibration. But thats just a small part of the many issues found with this motor. Over all this motor was poorly cleaned and assembled.
Glad to say now though it runs like a top and I'm very happy with the combo in this car. It's like a whole new car.
 
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