There are a number of problems, but in short, the D44 has the main problem of being non-standard. When placed in the ZJ, there was a custom D44 built where the center is built with an aluminum case instead of iron. Because of this non-standard design (no one really seems to be able to explain why this was actually done) there are not only problems with a new part, and issues with a new design such as noise, and reliability of parts, but there are currently no upgrades built for this axle.
Do NOT jack up the rear of the ZJ from the bottom of the differential like you normally would, as this can cause damage to the case.
Reports are that the foreign (at least in South America) manufactured ZJs come with full iron D44s both front and rear. If anyone knows how to get these parts into the United States, please contact me at the address below.
If anyone has more information or pictures, please contact josh@jeepzj.com
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