Odd contaminant in brake fluid

[Clanky]

Hi,

Today I took the rear caliper off my bike because it had started to bind. I split the casing and saw that there was a lot of tiny sponge like clumps floating in the fluid and similar but harder bits near the seals. In some places there was glazing that looked like brown varnish. I think the glazing is where the piston rubs slightly against the bore of the caliper.

The fluid was clean enough, still a clear honey colour but is probably due a change going by when the previous owner said it was last done.

The rubber seals had been put in without any grease and both dust seals had been caught and pinched outwards between the piston and the outer face, so this was cause of the binding.

Can't understand what the sponge like/tapioca mess is in the fluid. I'm going to clean the rest of the system thoroughly now but I wondered what would cause this?

[taggy]

could it be from when they last did the fluid? not cleaned out the res. propery or allowed stuff to fall in? if there aren't bits missing from the seals etc, i guess it could be from the lines themselves? if they used certain fluid I believe it can cause the rubber to perish?

[bokka]

hi clanky,i had the same problem with my rear caliper its just due to age.all you need to do is clean the caliper with methlated spirit and replace the seals including the small o ring but do not use grease only use brake fluid to lubricate the seals,when you put the pistons in turn them in like a screw to avoid any pinching.i also replaced my brake line front and rear for about £60 from goodridge.only use dot 4 brake fluid.the o rings can be difficult to find,if you have a problem finding them ill give you the details of a suplier.happy tinkering...bokka

[Clanky]

Hi Fellas,

Thanks for the answers. I don't think it was foreign debris, looks almost like an organic reaction in the fluid.

I will be stripping the rest of the system down and clean it all up with meths. Now's a good time to go for a new braided line.

Bokka, I have searched for the 'o' ring inside the two caliper halves but could not find it on any parts fiche. If you could post the details of your source I'd really appreciate it. Any reason for not using the assembly grease they give you with the seals?

Cheers

Nigel

[Nik]

Nigel,
what you found is the effect of U/V and water in your system.
It is very common here in the tropics. as Y-G said elsewhere brake fluid seems to degrade faster here (probably the high humidity and the high U/v content of the sunlight.
As for greasing the seals I only ever saw Y-G do it with brake fluid.

[bokka]

hi clanky,"the assembly grease" is to do with pressure and contamination the only thing that should be in the brake system is brake fluid.you can get the o rings from powerhouse automotive ltd,39 bailey street sheffield,s1 4eh.tel 0114 2811395....email enquiries@powerhouseautomotive.co.uk sumitomo joint seals.they also do the bolts if ya need them.hope this helps,bokka

[Clanky]

Thank you everyone for the advice.

Bokka, great help with the supplier I'll call them today.

Regards

Nigel