I posted this in the custom section as well. PM calipers with an Arlen Ness master cylinder. 2001 Custom build (not by me). Caliper pistons will not retract (sometimes); any ideas as to what fluid should be used in this configuration? My guess is DOT 4; any clues as to the cause of this problem? I am considering a system flush and fresh DOT 4 to possibly resolve the issue. Ideas??? Thanks

 

I would also look into replacing piston(s) and seal(s) as well, as your brakes are over ten years old now.

You more than likely use DOT 5 fluid in yours. My pm's are 96-97 era and they use DOT 5.