Are all the trans cases universal to their make? Meaning I could take any case half from a b18 trans and use it for another b18 trans or do they need to stay matching S80 for S80. Thanks

 

Transmission cases are mass produced, and should be treated as such. There is no guarantee that a given housing will have the same clearances of any other of the same part number. If you interchange housings of the same number, it is wise to clearance the new assembly in all respects, used or new provided they fit correctly.

All of the cutting parts will wear during production. This is why engine bearings have a clearance stamped on them. Its not that the part is defective if it has a C rating, its that the clearance is C units wide. You just have to build accordingly. Interchanging parts may complicate your build or make it overly expensive. In my experience, it is better to stay with matching parts, that way you can gauge the wear and correct it. Some units are more prone to damage or failure than others simply due to mass production.