Brake fluid loss

[Geoff Butcher]

My brake fluid light came on in December, not long after the MoT, when the brakes were OK. I assumed the pads had worn down and topped it up, but the light came on again today. I've looked under the bonnet, and inspected all four corners, but I can't see a leak. The master cylinder is quite new, the pedal feels normal and there's no white smoke from the exhaust, so the question is, where is the fluid going?

[Hans Efde]

Hi Geoff,
a) Are you really loosing fluid or is it an indication problem? Just check the level in your fluid reservoir. If it's an indication problem, you have a loose wire, probably on one of the spades on top of the fluid reservoir (no contact = high resistance between the 2 connections = light on).
b) If you are really loosing fluid and you haven't messed with the brakes, it must the master cylinder. Quite easy you should see drops hanging down the brake lines where they are screwed in the master cylinder. Or there may be fluid leaking between the pressure reducer and the body. That's a pig, mine keeps on sweating even with special hydraulic seals and lapped surfaces.
c) If there are no visible leaks outside the master cylinder, possibly you have an internal leak. That means it leaks down the main piston into the brake servo. In this case undo the 2 nuts and lift the master cylinder carefully (the brake lines are flexible enough). Quite clearly you should see brake fluid on the piston sticking out and possibly fluid on top of the rubber bladder inside the brake servo.
good luck, Hans