PSA - Rear brake line failure (cause and remedy)

[Leor604]

Just had a rear brake line failure, my fault.

When replacing rear pads, as you remove the caliper you may tug slightly on the brake line. This can pull some line through the rubber locating grommet. When you replace the caliper, the section of line between the caliper and the grommet will now have some slack. I swap pads a lot (for track days) so I think a little more line got pulled through each time eventually causing a significant bow in the line. If you're unlucky like me, the bow may cause the line to come in contact with the wheel hub. See the result below.



When you replace your caliper, give the line (between the grommet and the hard line) a little tug to take out any slack between the grommet and the caliper. That section of line should be as straight as possible. There is no relative movement here so no need for any slack. All the slack should be between the grommet and the hard line. Could also pop the grommet out of its bracket before removing the caliper, but I found it quite difficult to get the grommet back into the bracket (StopTech lines and grommet, others may vary).

On another note, when this happened I had NO braking. Pedal went to the floor. Luckily, I was in my driveway just setting the pads against the rotors. I thought our cars (all cars?) had a dual braking circuit that should still provide braking to three wheels should something like this happen. Certainly didn't work in my case. Scary.

[SteveYem]

Wow! Pretty scary that you had no braking when that ruptured. The parking brake still worked, right? I wonder what one would do if this happened when at highway speed.

Thanks for the PSA, I'm going to take a look at this the next time I have my rear wheels off considering that I changed my brake pads a few months ago.

[amz]

Wow! Pretty scary that you had no braking when that ruptured. The parking brake still worked, right? I wonder what one would do if this happened when at highway speed.

Thanks for the PSA, I'm going to take a look at this the next time I have my rear wheels off considering that I changed my brake pads a few months ago.

At highway you downshift as much as possible to initiate a controlled slow-down of the vehicle and, if absolutely necessary, hold the parking brake button in the engage position. I believe the handbook says ABS will take over and do it's best to modulate the rear brakes to keep you going in the correct direction while stopping the vehicle.

[rtl5009]

If you get a hole in the line you will have brakes until you run out of fluid in the master. Each time you press the brakes you will get some pressure but the fluid will bleed out of the hole. Essentially you have to pump the brakes over and over to maintain braking.

[agorich]

At highway you downshift as much as possible to initiate a controlled slow-down of the vehicle and, if absolutely necessary, hold the parking brake button in the engage position. I believe the handbook says ABS will take over and do it's best to modulate the rear brakes to keep you going in the correct direction while stopping the vehicle.

GOOD INFO! I will go through my booklet later when I get home.

[amz]

GOOD INFO! I will go through my booklet later when I get home.

When I first got the car, I kept mine in the bathroom for a month, read it cover to cover a few times.

Fun tip: we also have explosive seat belts

[Leor604]

If you get a hole in the line you will have brakes until you run out of fluid in the master. Each time you press the brakes you will get some pressure but the fluid will bleed out of the hole. Essentially you have to pump the brakes over and over to maintain braking.

Agreed, but I guess the rupture in my line was large enough that pressure was impossible to build. Pedal just went to the floor with little resistance.

Judging by how many times I pumped the pedal and how much fluid was left in the reservoir, I estimate you can get at least 10 pumps in until you drain the reservoir. With a small hole, it should be possible to bring the car to a halt.

Still surprised that we don't have some sort of a split hydraulic circuit to mitigate such a failure.

[timzcat]

All cars have a split system (FMVSS Standard 105, 1976; requires the master cylinder is divided internally into two sections, each of which pressurizes a separate hydraulic circuit).
Just because you were able to drop the pedal wouldn't mean you had no brakes, you had a leak so the pedal could drop after all other pads were against rotors. Had you been driving the car would have still slowed until as stated there was no fluid left in the reservoir.