Yamaha's iconic Blue Spot calipers are a great set of stoppers and are often bought second hand from breakers to upgrade the brakes on older bikes such as the FJ1200, onto which they bolt straight on.

The problem is that people don't change their brake fluid as often as they should and these brakes suffer from corrosion. When corrosion gets behind the seals, they are forced against the pistons seizing them. As these calipers can't be split you can't use a standard piston removal tool so you are stuffed. When the calipers were made they were line bored and plugs inserted, which are secured in place with the 'blue spot' nuts for which there are no tools available. Yamaha claim in their manuals that they can't be taken out and death will be the reward for those who try :)

In reality they can be taken out with this tool and a 22mm socket/ring spanner. This British made tool from Laser Tools is machined from aluminium so that it is less likely to mark the soft 'blue spot' nuts.

There is an 'O' ring sealing the plug behind the blue nut, which Yamaha do not supply, but we can! The cynical amongst you might think that Yamaha are better off selling a whole new caliper, but we couldn't possibly comment! We must however emphasize that these are NOT standard 'O' rings. Standard 'O' rings are not compatible with DOT 4 brake fluid; use them and Yamaha's warning might be brought home. Once the plugs are out it is easy to drive out the outer seized pistons with a drift and the inner ones can be removed with a professional brake piston removal tool. If the pistons are well stuck you might need a collet style tool. Gently warming the caliper with a heat gun will help as will liberal use of ACF50.