# No break-pedal pressure ONLY when outside temp is above 75 degrees and sunny **URL:** \ **Category:** Maintenance/Repairs\ **Tags:** accord, honda\ **Created:** [May 21, 2015, 7:14pm UTC](https://community.cartalk.com/t/no-break-pedal-pressure-only-when-outside-temp-is-above-75-degrees-and-sunny/90049 "2015-05-21T19:14:05Z")\ **Posts on this page:** 4\ **Page:** 1
**Author:** ![Nan123](https://avatars.discourse-cdn.com/v4/letter/n/ac8455/32.png) [@Nan123](https://community.cartalk.com/u/Nan123)\ **Post date:** [May 21, 2015, 7:14pm UTC](https://community.cartalk.com/t/no-break-pedal-pressure-only-when-outside-temp-is-above-75-degrees-and-sunny/90049/1 "2015-05-21T19:14:05Z")
I have a problem about which the mechanics I have asked are baffled: In cool, cloudy or sunny weather, my breaks and break-pedal pressure are fine (the mechanics have said I have good fluid, brakes, etc.–they can find nothing wrong–and, of course, it never has a problem when they test-drive my car). However, when the weather warms up and it’s a bright, sunny day, my break pedal loses pressure and slowly sinks to the floor–a dangerous thing at intersections. There’s slight pressure if I pump the pedal constantly while at a light; but, without pumping, the pedal immediately sinks to the floor. This is a real problem, because this problem always occurs right when mechanics are not near or not open for business–and none I’ve talked to have ever heard of such a problem. The bright, hot sun’s affect seems to be key, because if it’s 80 degrees outside and cloudy, I don’t have the issue–but, then again, I don’t usually run the air conditioner if it’s cloudy. As such, I’m not positive; but, this may be tied to when I turn on the air conditioner–as though the two share the same vacuum system. Anyone have any ideas regarding this? ---
**Author:** ![SteveCBT](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/stevecbt/32/3192_2.png) [@SteveCBT](https://community.cartalk.com/u/SteveCBT)\ **Post date:** [May 21, 2015, 7:21pm UTC](https://community.cartalk.com/t/no-break-pedal-pressure-only-when-outside-temp-is-above-75-degrees-and-sunny/90049/2 "2015-05-21T19:21:55Z")
I would suspect the master brake cylinder. It may be marginal and when it gets hot the seals get too soft allowing fluid to leak. I would try another mechanic, this should be easy enough to check and fix. They could put a hair dryer or heat gun on the master cylinder to see if they can duplicate the problem. ---
**Author:** ![VDCdriver](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/vdcdriver/32/30_2.png) [@VDCdriver](https://community.cartalk.com/u/VDCdriver)\ **Post date:** [May 21, 2015, 7:26pm UTC](https://community.cartalk.com/t/no-break-pedal-pressure-only-when-outside-temp-is-above-75-degrees-and-sunny/90049/3 "2015-05-21T19:26:33Z")
Normally, when somebody describes a **brake** pedal sinking to the floor, it is a sure sign that the **brake** master cylinder is worn-out and needs to be replaced. But, if this is somehow tied-in with vacuum pressure, then it may point to the **brake** booster being the source of the problem. However, even if the **brake** booster is the issue, you would still have **brakes** , with the problem being that they would require much more pressure on the pedal, and the pedal would barely yield when you press on it. I think that this is almost surely a case of a worn-out master cylinder, but I think that you need to consult a new mechanic before you break something as a result of your **brake** problem. **;-))** ---
**Author:** ![Howie32703](https://avatars.discourse-cdn.com/v4/letter/h/2acd7d/32.png) [@Howie32703](https://community.cartalk.com/u/Howie32703)\ **Post date:** [May 21, 2015, 7:26pm UTC](https://community.cartalk.com/t/no-break-pedal-pressure-only-when-outside-temp-is-above-75-degrees-and-sunny/90049/4 "2015-05-21T19:26:44Z")
How is the level of “BRAKE” fluid in the master cylinder ? if ok sounds like the master cylinder is flaky. Try this…very gently apply pressure to the brake pedal, does it slowly sink to the floor ? Now slam hard on the pedal a few times like in a panic stop. If this gives you some pedal the seals are worn in the MC. Do this with the engine running and in Park or neutral if a stick, and not going down the road !