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AO Silver Member
Join Date: Jan 2009
Location: United Kingdom
Right, I'm not sure where this bolt for an Allen key is but on the 159 you have to use a suitable wind back tool and yes the laser one works perfectly. You will see on the face of the piston two holes about an inch and a half apart. Thus is a key way, designed for a caliper wind back tool. The wind back tool has a removable face which fits perfectly in to the piston key way, then just insert the tool in to the face, position the pressure plate against the other side of the caliper and start winding the tool against the pressure plate.
This will simultaneously turn and push the piston back in. It's really really easy. This is the procedure laid down in elearn, the official workshop manual. Helps to remove the top off the brake fluid reservoir as well.