Coming down the hill to my house after a ride the other day – it’s about 200m of say 1:6 – not severe by any means – I decided to test my brakes by riding fast down it and then braking as hard as I could whilst pedalling really hard. Well they worked ok until a certain point when they suddenly got loads worse.

Now I know about brake fade caused by wet brake fluid boiling, but this didn’t seem to be the case. It really wasn’t a long hill – barely 200m as stated above, and the lever didn’t go very spongy. Maybe a bit but I couldn’t really tell since I don’t usually brake that hard. The discs were very very hot, and smelling kind of singed – so it’s possible there was some kind of contaminant.

Thing is, I sat and waited a bit and they stayed crap. It’s almost as if a bit of fluid leaked out and spilled on the pads, but I didn’t see any signs of that at the bleed valve. Can fluid leak out of the piston seals?

Ideas?

It certainly can leak from calliper seals

You might well have overheated them and glazed the pads

sounds like glazed pads.

one effect of over heating, not sure what defines whether brakes glaze or fade first…..
big rotors and composite pistons keeping heat on the pads but out the fluid?

caused by gas in the pad itself getting so hot it is forced out of the pad surface and creates a varnish/glass like surface on the pad.
also can cause a small amount of smoke and a distinct burning odour.

sorted by sanding off the top of the pads, and re bedding them in.

what they said, you may have also boiled them

if you realy caned them then you may have blown the seals.

not sure about glazeing, i used to ride my bike arround Crookes to bed the pads in, wasn’t happy untill the rotors were blue and the anodising on the pads had gone a funny colour. But that was only ever enough force for me to pedal against downhill (1in3 to 1in6 hills) and still maintain 10mph or so.

You might well have overheated them and glazed the pads

Yeah but it happened suddenly – like they were working well then squit – they got worse.

Thinking back – there may have been a small change in lever travel too which would support the seals leaking idea. They still seem to *operate* fine tho.

Does one replace one’s piston seals periodically?

caused by gas in the pad itself getting so hot it is forced out of the pad surface and creates a varnish/glass like surface on the pad.
also can cause a small amount of smoke and a distinct burning odour.

That sounds like a good theory to me. Will take a look at the pads. I probably do need bigger rotors tho.