Tales from the Auto Shop: Oh Yes You Will Pay

[Chromatix]

They had cooled off, I guess!

Mmm, sounds like boiling brake fluid - which can happen if your brakes get hot enough. In the vapour phase, it loses all of those nice hydraulic properties that the brake system relies on to transmit your pedal command to the calipers.

Engine braking is one way to prevent that from happening.

[Mikkel]

Mmm, sounds like boiling brake fluid - which can happen if your brakes get hot enough. In the vapour phase, it loses all of those nice hydraulic properties that the brake system relies on to transmit your pedal command to the calipers.

As I understand it, brake fluid absorbs water, thereby lowering the boiling point. Old brake fluid can contain a lot of water. If a steam bubble forms, it can be compressed and the brake pedal floors itself .
That's why the mechanic (hopefully) will tell you that the brake fluid is too old and ask permission to change it, even if it works perfectly.

[wolfie]

That's why it's recommended to replace brake fluid every 2 years (that and aged/deteriorated brake fluid tends to "eat" seals - cost me a clutch slave cylinder a few years back, car uses brake fluid as the hydraulic fluid in the clutch).

Other vehicles are designed with a "total loss" brake system - the fluid is used once, and when you release the brakes the used fluid is dumped on the road. I've got one like that.

[Nunavut Pants]

Water in brake fluid not only is bad for seals, but it can RUST the steel parts on the inside of the brakes! Which is not something you want.

I've BTDT with the boiling brake fluid, BTW. Scary as hell going into a corner at triple-digit speeds, only to have the middle pedal go straight to the floor. Fortunately I pumped the pedal and slowed enough to make the turn. I naturally took it much easier for the rest of the lap, and pulled into the pits as soon as I could.

It kind of sucked to lose the last 5 minutes of the 20-minute run group, but better that than running out of track and winding up in the wall...

[protege]

They had cooled off, I guess!

That could be it. But, those cars had a well-deserved reputation for brake problems. I remember my mom moving the car from the driveway to the street...and finding herself without brakes. We're talking about 20 feet, folks. No way they could have heated up that much. Also, the car would suddenly lose brakes during the night. That is, you'd drive home from work without problems. Leave the car in the driveway overnight...and then find the pedal hitting the floor at startup the next day. Never figured out what was wrong with that stupid car--it destroyed itself not long after.