Is there a trick to compressing the rear disc piston?

You need a brake caliper unwinding tool, either a VAG model from Metalnerd, or a universal unwinder (but a 6 piece kit won't work unless it specifies a VAG product). A brake "cube" works if you have the skill to use one. "Cubes" are in the $12 range. -- end comment from 'unitacx' -- I do not have personal experience with thes problem, but am about to. My Golf is presently dissasembled, and will have freshly turned rotors and new pads available for installation this weekend. In preparation for this job, I searched the web and found the following link: http://forums.vwvortex.com/zerothread?id=2025629 You will find a discussion about retracting the rear caliper in detail here. In addition, my Haynes manual for the VW Golf (and others), 1999-2002 says the pistons have to be rotated to retract them (Chapter 9, pg 9-5, picture 3.6h). As the above link discusses, just how to rotate them is somewhat unclear, but the picture at the top of the link is helpful. If I understand the discussion properly, you can rent this tool from some some auto parts places - I have none in my neighborhood, so I can't comment. If the comment from "animaniac" 6-12-2005 is understood, the piston has two bores in it's surface, which are intended to accept what is technically called a spanner wrench which is used to rotate the piston (evidently clockwise) and make it retract. (See the McMaster-Carr site, and search on "spanner wrench" for a picture of a spanner. My guess is we need a 5480A11 or similar) Note from all the VWvortex discussion: Excess force can damage the piston mechanisms, so don't use brute force on this one. The lesson learned is to use the internet, and search for your query. I have found the VW vortex forums very valuable. Try them - you will like them. Hope this helps. Skrotzki Reno, NV