Brake Advice, please.

[PC1]

Hi, My 1200Gs failed mot due to front brakes binding. I have stripped and cleaned the brake calipers (pistons out all ok) I have checked pins and pads all ok. The pistons go back easily with a small bar but will not release by themselves. Is this likely to be a master cylinder problem? How easy is it to change a master cylinder? Mot needed by end of month so I can tax bike. Any advice appreciated.

 

[mermoto]

Are the seals OK? they are vital to be in good condition as I believe the shape normally assists pulling the pistons back in to the caliper.

 

[PC1]

If you mean the seals in the cylinders, yes they are in good condition.

 

[wust588]

Sounds like the pistons are not free enough in their bores.

 

[Bear]

It's not unknown to get damp behind the seals, which encourages the alloy of the calliper to oxidise. This pushes the seals against the pistons, thus causing brake binding. The only way to find out is to remove the pistons then the seals. Before doing this, make sure that you have everything to hand to bleed the brakes afterwards as you'll lose all the fluid in the wheel circuits when the pistons come out.