Why do most rear disc conversion kits require the use of green bearings? I know the Dr. Diff kit uses stock tapered bearings. What is different about his kit compared to others?

If the caliper brackets are designed to simply bolt in place of the drum brake backing plates without changing the original dimensions, any bearing that fits a drum brake will also fit the caliper bracket.

My kit will accept Green bearings or adjustable, Set 7 tapered wheel bearings.

The other part of the equation is that most tapered rear wheel bearings are set with, or wear to the point, that they have a significant amount of endplay. The problem is that the rotor can now move axially by that amount, pushing the piston(s) back. This results in a disconcertingly low pedal on the next brake application.

Experience has proven, however, that the stock Timkens can be safely run with very little endplay (I run 0.003"), or even a skosh of preload, mitigating the problem entirely. So you can keep your Timkens, having your cake and eating it too!

Rick