Automatic Transmission Details

The Magnum engine uses the standard small block bellhousing bolt pattern, allowing for the use of 904, 727, etc. If you already have a small block V8 transmission, the engine will bolt up, but there are some important details to address first.

External Balance
The 5.9 Magnum engine is externally balanced and is different than all other Chrysler small blocks. The 5.2 Magnum is internally balanced and similar to the LA 318 in this respect. 5.2 users can ignore much of what is stated below.

The LA 360 is NOT the same as the 5.9 Magnum, and using the flex plate, balancer, or converter for an LA 360 will result in vibration and engine damage. You must use the correct parts!

LA 318s and steel crank 340s, and 5.2 Magnums are neutral-balanced, so there are no weights on either the flexplate or the converter. Conversely, externally balanced Chrysler small blocks have one of two arrangements. Either the flexplate has counterweights  and the converter is “neutral” balanced, or the converter carries counterweights and the flexplate is neutral-balanced.

The 5.9 Magnum uses a weighted flexplate and a neutral-balanced converter from the factory. To make life simple, be sure to get the flexplate with your engine. With the weighted flexplate, simply use a neutral balanced converter, these are readily available for most transmissions. We recommend this method.

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When you attach your converter, you will likely have a slight mismatch on one of the bolt holes on the Magnum flexplate. You will need to slightly enlarge one of the holes for proper fit. We recommend a decent sized rat-tail file, which makes quick work of this task.

If you do not have a stock magnum flexplate, you will have to run a neutral-balanced 360 flexplate and use a Magnum-balanced converter. Custom converter shops, like Ultimate Converter can build a converter balanced for a Magnum, but finding shelf converters balanced for Magnum engines is difficult if not impossible.


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