I got the center diffs yesterday and installed one on my Rally. It seems like it needs to be shimmed. Traxxas told me they don't know why some do this and some don't but they have a teflon washer available to fix it.
Anybody run into this?
Nobody has had this problem?
It doesn't need shims. It needs material removed from the center diff cap. The cap was pushing on the pinion gear causing the rear diff to mesh poorly.