Trouble replacing brake caliper piston after rebuild
 

We're rebuilding the calipers on our 1970 911T. After we removed the pistons and rebuilt the caliper, the inboard piston on the passenger rear caliper does not go in all the way. It seems to hit a solid piece of metal.

We even tried to put the piston back in without the seal, and it is still stopping half-way.

We think it might be getting hung up on the nipple in the center of the bore of the caliper

Any ideas of what might be causing the piston to not go in all the way?

Anti-knock-back mechanism, perhaps? Did the outside piston go in "all the way"? There is a pin and spring system that attaches to the piston and the back of the bore to keep the pistons from going too far back into the bore and so keep the pedal high.

Flieger, you were right. We used a c clamp to push the piston back into the caliper. I had never had to do that previously. Thanks for the help.