Sticking Brake Piston

[Skyenet]

Had a busy few days doing a load of jobs on the bike. These included replacing the tyres with Avon Azaros, replacing the disk bobbins and rear brake pads. However when all was back together I found that my front wheel was quite stiff to turn.

Took the callipers off to check the wheel moved freely on its own and it was fine. This then pointed towards the problem being my brakes. Once I looked at the callipers I found that one piston on each was sticking. On both it was the same one, inside top piston. Brushed away loose dirt and then used spray brake cleaner. Once clean I kept working on pushing the pistons in and out. Soon had three psitons on each calliper moving freely. However I could not get the other on on each moving freely. I have managed to get them moving quite well but not as freely as the others and reckon they could still cause the pads to bind. Any ideas of what I could do to loosen them up more? Its an ABS model so if any stripping work is done on the brakes I will need to get it bleed at a dealers and have been quoted around £70 for that alone. Really can't afford that at the moment.

I reckon the reason it was fine before I did the bobbins was that, although it appears the pistons were sticking, it was not causing any binding because the play in the discs (with loose bobbins) was not causing the pads to touch the discs.

[BillE]

You have one of two problems. A master cylinder that won't allow the fluid to bleed back into the resevoir(sp) or a the piston seals and bore are in need of attention.

Installing a kit in caliper is really easy to do and you should be able to bleed it yourself. Just do one caliper at a time and don't allow the fluid to drain out of the system, also pre-fill the caliper through the brake line bolt before hooking it up to the system.

Start your bleed process with pistons extended and bleed through the port. Then push both sides of the pistons back into their bores, forcing fluid back through the system into the master. This is kind of a reverse bleed and gets some of the air out. Then proceed with normal bleeding... then do the next caliper. After you have completed both sides bleed the entire system starting at the master, then the ABS modulator and finally the calipers.

If you have advanced bleed skills or tools then doing both calipers is an ok deal, but beware it can be rather tedious to get them bled.

[Skyenet]

Thanks for advice - Will overhaul the sticky pistons on Thursday with the help of Dickybeau, who luckily had a spare overhaul kit in his garage. I don't even have basic brake bleeding skills so will be glad of the helping hand. Will post back how we get on.

Hopefully it will get sorted on Thursday as there is a BMW run this weekend in Scotland and would prefer to go on the R1100RS. Luckily I still have the option of taking the F650 though. It now has a new set of Michelin Anekee tyres and new rear pads.

Iain