Forum

[jefrs]

There's a tiny wee pinhole in the clear plastic seal over the master cylinder but not in the air-tight neoprene membrane below that. Water vapour (gas) and air can get through the cylinder seals. When fluid expands it pushes that black membrane up and cannot go any further, nothing comes out. Old and low quality fluid seem more prone to this than modern stuff. The brake lever goes very hard and cannot be pulled back, the brakes are locked on.


This happened with the indian fluid in my C5, occurs regularly with my mountain bike and has beset me on old cars.

[papasmurf]

Well I have been tapping calipers using a bit of wood and a hammer to free them off for more decades than I care to remember. Usually it works, when it doesn't it is usually because the caliper can't "float" due to cag and corrosion "welding" it to the bolts.
If sorting that out doesn't work, it is service the calipers.

[PeteF]

I know how they breath Jefrs but if the headroom in the reservoir is used up then there is a serious amount of water in the fluid. Absorbsion only amounts to about 1% a year (usually through flexible pipes rather than seals)