Brake Pedal Sinks when hot

chrysler
brakes
pedal

#1

On one hot day (90 degrees) this week after driving on the highway for about 30 miles and then sitting at a light my brake pedal sunk about 1 - 2 inches. It did this again when IO stopped to park. This is an 2001 PT Cruiser with a standard transmission and 44k miles. The original brake, pads , rotors and calipers are apparently in good shape. I have not driven it under the same circumstances again and the problem has not re-appeared. Some additional background, this car has anti-lock brakes and requires a special diagnostic tool to release the abs system to bleed the brakes. I generally bleed my brakes every few years. A few weeks ago I decided to merely siphon off a few ounces of fluid and replace it with new Dot 3 fluid every week for about a month. I used certified Dot 3 fluid, but purchased an Off Brand name. Also, I?m getting ready for a longer (1000 mile) trip south where it will be even hotter than 90 degrees. Any thoughts?


#2

A sinking brake pedal is a sign that the brake master cylinder is leaking internally and requires replacement.

Tester


#3

Yup. You need a new brake master cylinder.


#4

Brake master cylinder is bad. In a panic stop…you may not.


#5

Reminds me of an old car I bought from a friend, as a fun fixer-upper. He said, “The brakes work. You just have to pump 'em.”

Yes, the master cylinder was the first part I replaced. Other brake parts, and tires, in short order after that.


#6

You may have moisture in your brake lines. If the pedal is only spongy in hot weather after hard braking, brake line moisture may be turning to steam … giving you a “rubber” pedal.