Master brake cylinder?

 

The last few days I had the impression that the brakes didn’t respond immediately when braking. I had to push twice on the brake pedal to have a normal resistance in the pedal.

I checked the brakes but there were no leaks and the master cylinder reservoir was on the maximum level, so there was no loss off brake fluid.

So on the way back home I tried to push hard on the brake pedal at first pedal stroke and I had the feeling something snapped. At the same moment the brake warning light came on and it felt like I lost a part of the braking force or was it the brake servo not working?

 

I slept the night over it and in the morning I decided it should have to be something with the master brake cylinder because this is where the warning switch is.

I took the master cylinder off and took the primary cylinder apart but all looked well. Then I took the secondary cylinder apart. At first I didn’t saw it but after a good look I saw one of the O-rings was missing. I looked inside the master cylinder but couldn’t see the O-ring (number 12 on the right side in the drawing). Then all of a sudden I found the O-ring on the cloth where I put the parts to keep them clean. Now I don’t know what happened but normally this O-ring can’t just fall out of his lodgment so I guess this was the snap I felt when I pushed the pedal real hard. But I’m still tinkering; how on earth can an O-ring become apart from his lodgment when it’s inside its cylinder wall?

I’ve put everything together again and braided the brakes and all seems fine now; no warning light and brakes are working properly. But I still have to do a real road test so we’ll see how it goes.