Model 28-2. Old rod had buggered knurling and looked out of round on that end.

Replacement came today. Brownells

I installed and closed the cylinder.
When I press the cylinder release the rear does not unlock....

I know the side plate needs to come off to unlock it.

What would cause this?

On the plus side the drag on one chamber in single action is gone

Sounds like something is too long. The rod is bottoming out in the front before the back end of the rod clears the recoil shield. Are you sure you got the right rod?

__________________
jj

I was wrong
Its the front not unlocking

The fix is simple:

Use a thin pocket knife blade to retract the front lock enough to clear the end of the extractor rod, and open the cylinder.

Make sure the extractor rod is tight. Use a fine cut mill file to trim a couple thousandths of an inch off the end of the extractor rod. Just enough for it to reliably open and close the cylinder. This is normally done when fitting a new extractor rod.

Thank you all for the help