Brake failure

Ever had one of those days?

This morning as I was heading out to the gym my brakes failed. Not good. I'd got to the end of my street and braked, made it to the mini-roundabout and braked, but when I pressed the brake pedal on approaching a junction with the main road, nothing happened! Well, until I eased down to second and eased up the handbrake that is.

I put on my hazard lights, turned around, and drove back home at 2mph as I only lived about a thousand yards from where I was. Lucky the brakes didn't fail when I was on a major road, or if I was going faster than 10mph!

Back home I checked the brake fluid reservoir to find it was almost empty. I inspected under the car and all four wheels but could find no visible leaks. When I topped up the reservoir with more brake fluid it went down quite fast so I knew something was not right, but still no visible leak.

Working from rear right, rear left, front left to front right, I jacked up each wheel and undid the bleed nipple and proceeded to bleed the brakes to ensure there was no air in the system.

As there is only me bleeding the brakes, what I do is I attach the bleeding tube to the nipple and have the other end of the tube dangling into a glass jar on the floor. I have the drivers door open and my left arm in the car with my left hand pumping the brake pedal. This allows me to look under the car at the jar, whichever wheel it is currently at, and I can see if any brake fluid is coming out and any air bubbles. It works for me anyway.

Each time the brake fluid level in the reservoir got lower I topped it up. Once finished I topped the brake fluid level up to max and put the cap back on and re-attached the electrical spade connectors.

I sat in the car and put my foot on the brake pedal and started the engine. The pedal dropped about an inch so I know the servo is still working. I then drove the car slowly back and forth on the drive to test the brakes, then in the road when there is no one about, and finally I took it around to the bottom of our estate where there are no cars and tested the brakes by performing emergency stops. All seemed fine.

I drove the Mini to the gym and back and checked the brake fluid level in the reservoir and it hadn't moved, which is a good sign. The brakes also feel fine.

I've tried to work out what caused the brake failure and the only thing I can come up with is that I haven't checked the brake fluid level in over three weeks. I usually check all fluids in the Mini once a fortnight: radiator, oil, brake fluid, carburettor dash-pot oil. But I haven't looked in a while so maybe it was getting low and started sucking in air?

The only way I can think of the brake fluid level getting low is if the pads were getting worn, which was forcing the pistons out more, which lowered the fluid level in the reservoir. Strange though as I've changed the front pads not so long ago and the rear shoes were ok when I adjusted the handbrake for the MOT. But then I've done quite a few miles since then, and a bit of braking.

Update: My Dad had a suggestion in that I should check the rear brake drums for any leakage or contamination as the rear brake cylinders may of leaked and the drums may contain DOT4 brake fluid, which would not be good as it would mean that the rear brake shoes would be contaminated, thus reducing braking efficiency.

It only takes half an hour to remove both the rear wheels, the wheel hub covers, inspect the cylinders and brake shoes, and reassemble everything. Luckily both cylinders were fine but it's worth me pointing this out as worth checking as cylinders can fail and fluid could leak out of those rubber boots.

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