Just about any motorcycle will suffer from sticky brakes at some time in it's life, ofen it won't be noticed until MoT time, or far worse the first time you try to ride your bike over wet grass. You may notice that the bike is getting harder to push - it sort of feels like the tyres are flat. It's nearly always down to the same thing- sticky pistons in the brake calipers. More precisely it's the seals that jam the pistons due to a build up of corrosion in the recesses that they sit in. The calipers are designed in such a way that when brake pressure is released the pistons automatically draw very slightly back in to the caliper body to ensure that there is no residual pressure on the brake pads. As corrosion builds up the seals get tighter and tighter between the caliper and piston until the pistons can no longer retract. In severe cases they get so bad that the pistons can't move outwards, even under hydraulic pressure and the brakes become inoperative.
Exactly that happened on my Triumph 955i - the back brake was locked on solid and no amount of persuasion would shift it. The only fix was to remove the caliper and get it on the bench for some seriously medieval treatment. The tool for the job is a proper caliper piston removal tool as can be had for not much money - mine was about 25 quid and has repaid that 50 times over. The set comprises of a number of collets that range in size to suit every bike I have ever come across. There is a tee bar in there and a slide hammer, although I usually find the pistons are too tight for the slide hammer to have much impact on. The best tip I can give is hold the tool rather than the caliper in the bench vise , twist the caliper in an anti clockwise direction so you are always effectively tightening the collet in the tool. The collet expands as you tighten it, if you turn the caliper the wrong way all you will do is loosen the grip on the hollow piston.
The pistons in the Triumph caliper were so tight that I could not move them at all, they were the worst I have ever had to deal with. I had no option but to get Mr Blowtorch out and teach the thing a lesson in humility. A thick rag was needed at this point as I had to get the whole thing pretty hot before the grip was loosened. Both pistons eventually came out and to my surprise they were in perfect condition.
It's not a difficult job to do if you have the right tool, if you don't then it's nigh on impossible, don't even think about trying it, the job will end in tears. i have seen loads of calipers where somebody has tried to grab the end of the pistons with mole grips and all they have done is damaged the piston - if you do this and the seals leak you lose your brakes. That's a bad thing that can really mess up an otherwise perfectly good day.
With the pistons out the seals are usually very easy to remove, I use a dental pick. On these calipers the dust seals had gone extremely hard and brittle, I think they were cheap after market replacements. The real problem though was the corrosion in the grooves that the seals sit in - it was really bad and took a lot of cleaning with dental picks and a rotary brush in my Dremel multi tool. This job has to be done really well or the new seals will be too tight and you will be back to square one.
Another thing to note is that when you come to install new seals you need some proper red rubber grease, do not use any other sort of grease as mineral based greases will decompose the rubber seals over time and cause brake failure. If you buy good make seals they usually come with a small sachet of the right stuff and you only need a tiny amount to just help things go together nicely.
Only one final thought - some Tokico calipers have inserts in the pistons that are anti squeal devices, there make removing the pistons a complete pain. I have never found any way of removing there inserts without destroying them, I have never found a source for replacements either, if anybody knows of a solution I would love to hear from you in the comments section.
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