posi install difficulties

[Alex Hayley]

I am replacing the open differential with a posi unit while reusing the original ring gear and pinion.

I put the new pinion bearing on the original pinion shaft with the original shim. Installed the inner pinion race in the housing. Set the pinion in
the housing with the correct preload(15 pounds/inch). I Installed the original ring gear on a new posi unit. Then I installed the new posi unit with new
bearings in the housing with the original shims. The carrier would not turn once the bearing caps were snugged down loosely. The posi unit did not
seem to seat properly in the housing with the shims installed. With all shims removed on the side opposite the ring gear, the posi unit will seat but barely turn. Thinking that the position of the pinion was causing the binding, I removed the pinion, put the posi unit back in with all of the shims and it turned just fine. Could the posi unit be placing the ring gear too close to the pinion? I was under the assumption that the posi unit would sit in the same position allowing the use of the same ring gear and pinion. Is there something obvious I missed? Could there be a problem with the pinion?