Brake Failure

Several days ago, my daughter was stopped at a railroad crossing in her 1993 Subaru Legacy, automatic, waiting for the train to pass. She had her foot on the brake until traffic began to move, when she released the brake and began to move. Traffic immediately slowed so she again pressed on the brake. Her brake pedal (she said) went to the floor, her car didn’t stop, and she hit the car in front of her. Our mechanic checked the brake system and all seems to be in order. My question is: can a brake system fail one time, then be OK again? If so, what part of the system is the likely culprit?

Her brake master cylinder is worn out and is failing. Have it replaced immediately because this symptom will recur again periodically until complete brake failure results.

In addition to the master cylinder, I would suggest replacing your current mechanic with one who has better knowledge of what this symptom indicates. This guy is not knowledgeable enough, and his lack of knowledge could wind up killing your daughter and/or other people.

If the brakes were overheated, maybe the brake fluid had boiled to the point of adding vapor bubbles. Once they had a chance to cool, the fluid returned to a liquid state, and worked flawlessly. This is common when the brake fluid has never been changed, especially a 16 yo car. Brake fluid is hydrophillic, meaning it likes to absorb moisture. This moisture reduces the boiling point of the brake fluid, and reduces it’s anti-corrosion properties. Have the brake fluid flushed out and replaced with fresh.

I second this opinion on the master cylinder. I’ve had this happen on 2 different cars: 1) a 1965 Rambler; 2) 1978 Oldsmoblie Cutlass. In both cases, the master cylinder wore out on the inside and the brake fluid would slip past the piston. Sometimes the brakes were fine and sometimes they didn’t work. I would change the master cylinder right away.

Your car has a dual braking system. The chances of BOTH front and rear brakes failing at the same moment are REMOTE. There is also a brake warning light that should have come on if ONE of the systems failed…I would not condemn the braking system until a FAULT can be found.

I again side with Caddyman, total brake failure that cannot be duplicated,just doesn’t happen. The simplest explaination is the most likely, and that explaination is driver error.

I concur. I’ve had this happen to me on a couple of vehicles as well. When the master cylinder starts to fail, it can act just like this. Be sure to bleed the brakes after you replace the master cylinder.

I disagree with the driver error concept. A similar situation happened to me when I was a new driver. OK that was 1959 and I was driving a 1952 Studebaker Commander with 62,000 miles on it — but it did happen. I would come to a complete stop without any problems; however, if I was stopped for any length of time with my foot on the brake the pedal would periodically slowly sink to the floorboard. Several mechanics checked the system, bled the brakes and checked for leaks but could never duplicate the problem. Problem was identified as “New Driver”. Only after the car rolled into traffic one day while I was stopped on hill with my mother in the car did my parents take serious notice and have the car checked out by a “brake specialist”. Short story … there was a pit hole inside the bore of the master cylinder that would allow the fluid to seep by. It was probably a casting defect when they made the master cylinder and it nearly cost me my life! Get the master cylinder replaced … FAST.

You are relating an issue regarding 1940’s (or even earlier) technology, your experience does not apply to the OP’s 1993 vehicle.

You old guys that can’t let go of days past, well I will use todays language lol,lol,lol,lol,lol,…

Without any leaks and the pedal going to the floor, it’s usually the master cylinder.

That old 1952 Stude had a SINGLE cylinder master cylinder in it. It became common to put in double cylinder master cylinders in the mid-60’s, splitting the brake system into two separate circuits. This gave a safety factor that those old classics never had. It is extremely rare for both circuits in a modern brake system to both fail at the same time.

The pedal drops to the floor but nobody can make it happen again…Master cylinders either work or they don’t…I have seen a slow fade that ALMOST goes to the floor as one chamber leaks out, but an instant drop to the floor with NO braking response that can not be repeated…Give me a BRAKE!

Your 52 stude had a single piston master cylinder. The 93 subaru has a dual diagonal master cyl. The failure and healing of both sides of the system at once has huge odds against it. The likelihood is either her foot slipped off the brake pedal or there was something under the brake pedal (like her other foot). If it is the latter she will be firmly convinced the brake failed because she was pressing down on the pedal and couldn’t stop the car from moving.