Venting Brake Master Cylinder

[TANGO7]

Should the cap to a brake Master Cylinder be vented? I have had to adapt a cap to fit my Cylinder and wonder if I should have a small vent hole in it. I seem to recall older style caps had such holes.

[7 wonders of the world]

Old design had a small vent hole that was shielded internally to help reduce discharge whilst enjoying the cr.

Later designs have a small internal bladder which seals the fluid form the outside world preventing hygroscopic water ingress but still allow for expansion and fluid migration due to pad wear. Naturally this design should stop fluid discharge whilst cornering too, however I've had to return a couple of AP 'Race' caps as the threads were imperfect and 'popped' over the last thread before being tight.

NB The race caps required the OE deflector to be removed prior to fitting.

[7 wonders of the world]

...forgot to mention I ended up using a Girling cap with the AP bladder on the AP race master cylinder.