# Brake Pedal Sinks when hot

**URL:** <https://community.cartalk.com/t/brake-pedal-sinks-when-hot/34147>\
**Category:** Maintenance/Repairs\
**Tags:** pedal, chrysler, brakes\
**Created:** [July 28, 2009, 3:20pm UTC](https://community.cartalk.com/t/brake-pedal-sinks-when-hot/34147 "2009-07-28T15:20:28Z")\
**Posts on this page:** 6\
**Page:** 1

<div class="post-metadata">

**Author:** ![KCRoadRash](https://avatars.discourse-cdn.com/v4/letter/k/35a633/32.png) [@KCRoadRash](https://community.cartalk.com/u/KCRoadRash)\
**Post date:** [July 28, 2009, 3:20pm UTC](https://community.cartalk.com/t/brake-pedal-sinks-when-hot/34147/1 "2009-07-28T15:20:28Z")

</div>

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?

---

<div class="post-metadata">

**Author:** ![Tester](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/tester/32/15976_2.png) [@Tester](https://community.cartalk.com/u/Tester)\
**Post date:** [July 28, 2009, 3:29pm UTC](https://community.cartalk.com/t/brake-pedal-sinks-when-hot/34147/2 "2009-07-28T15:29:02Z")

</div>

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

Tester

---

<div class="post-metadata">

**Author:** ![fitjeep](https://avatars.discourse-cdn.com/v4/letter/f/e79b87/32.png) [@fitjeep](https://community.cartalk.com/u/fitjeep)\
**Post date:** [July 28, 2009, 4:20pm UTC](https://community.cartalk.com/t/brake-pedal-sinks-when-hot/34147/3 "2009-07-28T16:20:08Z")

</div>

Yup. You need a new brake master cylinder.

---

<div class="post-metadata">

**Author:** ![missileman](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/missileman/32/1366_2.png) [@missileman](https://community.cartalk.com/u/missileman)\
**Post date:** [July 28, 2009, 6:20pm UTC](https://community.cartalk.com/t/brake-pedal-sinks-when-hot/34147/4 "2009-07-28T18:20:42Z")

</div>

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

---

<div class="post-metadata">

**Author:** ![shanonia](https://avatars.discourse-cdn.com/v4/letter/s/9de053/32.png) [@shanonia](https://community.cartalk.com/u/shanonia)\
**Post date:** [July 28, 2009, 7:21pm UTC](https://community.cartalk.com/t/brake-pedal-sinks-when-hot/34147/5 "2009-07-28T19:21:20Z")

</div>

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.

---

<div class="post-metadata">

**Author:** ![Gary123](https://avatars.discourse-cdn.com/v4/letter/g/c37758/32.png) [@Gary123](https://community.cartalk.com/u/Gary123)\
**Post date:** [July 28, 2009, 9:19pm UTC](https://community.cartalk.com/t/brake-pedal-sinks-when-hot/34147/6 "2009-07-28T21:19:48Z")

</div>

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.