Problem is 'more hydraulic than mechanical'

Q: We have a manual transmission 2000 Honda Civic with 36,000 kilometres. The car is well maintained: a complete tune-up twice a year. Recently, we drove on Highway 15 toward Montreal at 90 km/h. To give precedence to a car entering the highway, I lightly applied the brakes. To my astonishment, the brake pedal was all loose and went completely down to the floor. I changed fast into first gear to slow the car down and applied the handbrake. The mechanic at our garage replaced the brakes, but it seems nobody can explain how -without any warning -they could completely fail.

Do you have any explanation?

- Margrit Gluckman

A: Both mechanics we spoke with suggest a problem with the master cylinder could be to blame.

"The problem here seems to be more hydraulic than mechanical," said Marc Lebrun, co-owner of Total Auto Service in Pierrefonds."Afailureinthe brake pads or discs will not cause the pedal to go down completely to the floor. However, a leak in the hose or malfunction of the caliper or wheel cylinder will cause the pedal to go to the floor."

Pierre Brunet, a co-owner of Autotech Performance, also in Pierrefonds, says he has seen this happen before.

"A failure in the master cylinder would cause that type of problem," he said.

He provided the following steps to help determine what the issue could be: "Try,without the car running, applying the brake. Put your foot down and moderate the pressure between firm and loose to see if the brake pedal will not sink. If it does sink, it's time to condemn the master cylinder," Brunet said.

He added that even if the mechanic who repaired your car could not give you a reason for the brake failure, and if the pedal did sink in the test, you would be better off replacing the master cylinder for "your peace of mind."

Lebrun also had another suggestion.

"Given the age of the car,I would recommend a brake flush to clean out the hydraulic system," Lebrun said.

"Lastly, I would like to add that a complete tune-up does not necessarily mean that the brake hydraulics were verified."