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Discussion Starter · #1 ·
In need of some help.  I’ve researched everything I could find on a magnum360 swap but in the end have a very significant harmonic vibration. I swapped out the la318 for a mag360 out of a 98 ram. For engine balance I used the oe harmonic balancer and weighted Flexplate which came with 360 which I removed. I kept the 318 non weighted converter. Vibration begins around 2000rpm and gets worse with increasing truck speed or rpm.  The vibration is also present in Park-neutral with truck not moving. 
Not sure how to proceed. Is the converter causing this?  Ive read about the b&m flexplate BMM10242 but it’s Nla and I’m not sure if it would help.  Any ideas a where I went wrong?  Thanks
 

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I am fairly certain you need the weighted torque converter..I just pulled the 360 back out of mine after having done the same thing except I did not even fire it up.
 

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If the flexplate has weights, then you need a neutral converter like the 318 one you used. If the flexplate does not have weights, then you will need a converter weighted for a 360 Magnum or a weight kit and weld them on yourself. Depending on the year of the engine donor, it could have been done either way.

This is a weighted 360 Magnum flexplate. Note the large weight on the bottom:

 

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Discussion Starter · #4 ·
That Flexplate is exactly what I used which is what came with the engine from the factory as it had never been removed. Do I need some custom type converter or should I try a new la 318 converter from Napa or some flap store? If so where do you recommend I buy one.
 

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Are you positive it is exactly the same?  Both flexplates are identical except for the large weight.  If it has the weight, then I would check the torque converter for extra weights.  It should only have one or two small sheetmetal weights to balance it out neutral.  Any large or thick weights would be for balance offset and would need to be removed.
 

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I misunderstood that sorry..thought you removed the weighted flex plate.
 

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A 98 should have the weighted flex plate, IIRC, it started like 96.

Abranz, Are you sure it was a 318 you pulled out? Its not uncommon for some one to have a 360 with a 2bbl, and think its a 318. It could be that you have a weighted convertor for a 360, and the weighted flex plate.

What about the harmonic ballancer? did you change it? On the 360 LA, it was different, I do not know if it was for the magnum360.

Do you know the history of the 360mag?
 

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Discussion Starter · #8 ·
Yesterday I pulled the 360mag. The Flexplate is identical to the image posted and is weighted. The balancer is the one which came with it from the donor van and is oe.  The converter does not have the 120gram la360 weight. It has about a one inch sheet metal tab welded to its perimeter which I assume was to neutral balance it for the 318la it was behind.  I’m lost as to what to do.
Do I order a b&m Flexplate with the cookie cut out of it and buy a la318 converter?  I have no idea if my converter is balanced correctly neutral but it seemed to work with the 318. 
Am I correct in my understanding that to install the magnum 360 you need it’s correct balancer and either the b&m Flexplate with the cutout or the oe weighted Flexplate?  Then one of these need to bolted to a neutral balanced converter like one from a la318? What’s the correct part number for the b&m flexplate?

This has been a lot of work and $. I should have known better than start modifying shit. Never seems to work out for me.  Appreciate the help.
 

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it sounds like the only item you didn't reuse was the 360 converter - do you still have it and is it good?  Also, I don't think it matters, but IIRC the Magnum engines has a 90* bolt pattern to the flexplate (didn't have one of the tabs offset from the other three like the earlier 727-based transmissions), but I don't know if the newer converters can be bolted up in either of the 4 positions relative to the flexplate or if there is indeed a one-way-only way necessary to align the flexplate to the converter...?
 

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Discussion Starter · #12 ·
When I put the flexplate against the 318 converter 3 holes lined up and 1 was off about 1/8” . I enlarged that hole to mate the two pieces. I was on b&m website and I see they discontinued part 10242 which I think was the flexplate used for this.
 

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...I'm not certain...but I'm thinking your alignment is off because of that off-set not lining up exactly.  Anyone else confirm?
 

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Yep, I agree with Sam!  That old TC could make the weight off a bit.  But it hardly seems like enough weight for the amount of vibrations you're getting.  But some of these balance issues are touchy. 
Got the convertor from the 360 donor set-up around?  You could check out the lug locations & bolt pattern.  The newer TC would be a lock up & maybe also the different input spline & will not fit in an old trans without a major trans rebuild.
 
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