Brake failure ?5 min job? update.

[johnben]

Having stripped down the master cylinder and reaction valve the main culprit seem to be sediment, there was no sign of the seals breaking down just a lot of debris which I presume must have allowed the fluid to bypass the seals. It makes you wonder where it all comes from. The original brake reservoir did contain a filter of which the new ones do not, but the sediment was either too fine or was produced after passing through the reservoir.


Looking from rear of the master cylinder internally towards the reaction valve.

Master & reaction valve showing sediment on seals.

Reaction valve cover showing debris and sediment at lower exit tube.

Brake reservoir looking down showing filter and sediment.

[christopher storey]

It's a bit hard to tell but those seals look worn to me. The leading edges of them should be like a knife edge

[e-bygum]

John
As you say the repro brake reservoirs don't come with a filter neither do they come with the metal spigot which is a push fit in the outlet of the reservoir over which the hose fits. Without this metal spigot the generally poor quality plastic is easily broken when tightening the hose clamp and easily splits from the bottom of the reservoir if any tension is put on it.
I trust you did transfer these parts to your new reservoirs.
I found it quite easy to remove/clean/refit the filter and the metal spigot when I overhauled my brakes. My reservoirs contained about 1/2 inch of black gunge in the bottom. I chose to reuse them as the new replacements do not have a good reputation and they did clean up quite well with Jif.

[Heuer]

If you are using new reservoirs insert a short length of steel or brass tubing into the plastic nipple. This allows the hose clamp to tighten without squashing the plastic and also strengthens the whole assembly. You can get suitable tubing from model shops. Alternative, as already suggested, is to cut out the old filters and re-use them.

On the other hand if you change the brake/clutch fluid every two years it is unlikely to be a problem.