Piston broke!
The sad reality is that many bikers don’t seem to notice a deterioration in the performance of their life-saving stoppers, nor feel any great urge to change the brake fluid as sanity dictates.
Given that these simple, but essential components are saving your life, my bikes always have their brakes regularly serviced.
To service motorcycle brakes properly they must be disassembled. Moisture held in the hygroscopic brake fluid delights in attacking the bare aluminium alloy of the caliper bodies, particularly behind the hydraulic seal. As the aluminium corrodes, so it becomes crusty and the flakes of corrosion push against the rubber seal forcing it against the piston, preventing said piston from sliding as freely as one would want it to, and wasting the crucial mechanical effort required to squeeze the pads against the disc by fighting friction. To clean behind this seal you need to extract the piston and for that you will need
a tool. These range in price from a few quid to well over a hundred for the best type of kit. As with many things in life you get what you pay for, but I warn you: be mean and look forward to frustration and future unnecessary expenditure!
There are two common types of piston removal tools, the plier type and the collet set type. In my workshop I have numerous iterations of both types, but were I only to have one type it would be the professional quality collet set which I bought from Laser Tools 20-odd years ago. Yes, it was expensive, but it is still the best tool on the market and I would buy it again in a heartbeat.
If you strip your calipers regularly and never work on the brakes of less sensible folk or bikes that have been left unloved for any period of time, then a good quality pair of plier type tools is going to be fine. To demonstrate these tools for the pictures, I dug out a set of Tokico calipers I had sorted and then not used, so they are in reasonable nick. Even still, it was a struggle to extract a piston with the cheapest tool. The Laser Tool middle price plier tool is well made, but the love child of the brake tool and Mole Grips is the best I have ever come across. The beauty of this tool is that you can strip the pistons out of more modern multi-piston calipers, such as the six potter in camera, without splitting them, which is great if they are regularly serviced.
There is no way you would get the pistons out of the other caliper shown here without a collet type kit. If you work on abused bikes, as I do, then you will be wasting your money on anything less than the basic collet style sets. Sealey do a set that is very reasonably priced and should be well within the budget of anyone serious about restoring a bike. The Z1000 pistons here were seriously wedged in and I had to attach the slide hammer, from the set, to the tool and warm up the caliper with a heat gun before the sods would submit to my will. You can see why in the last photo. Lashings of ACF-50 will also help with free such mistreated brakes.
I have been accused of being elitist when it comes to tools, but years of experience tell me that money invested in good quality tools is never wasted. Even the best quality, professional tool here wouldn’t buy you two hours of time in a bike garage and the budget collet tool less than 60 minutes. A common practice seems to be to butcher the pistons by using Mole Grips or water pump pliers, but this destroys the pistons, costing more to replace than the appropriate tools, but of course such bodgers don’t replace the pistons! Darwin at work!