When my car is cool or cold, the brakes work fine. I have noticed in the last few summers that when the car is hot, and the A/C is on, my brakes get very soft...to the point that I can push the pedal to the floor. What is very bizarre is that I only have this happen when the A/C is on. Is there any relation to the drain on the system by the A/C that could cause this to happen?

 

Check your master cylinder for any leaks. If there is rust on the brake booster than your master cylinder is bad.

 

There's not much to go on here as there isn't much interaction between the two systems.
Normally, you'd think they would get harder....
A/C kicks on, rpm drops, vacuum to the brake Booster drops, pedal gets harder. Huuum

Has the brake fluid ever been changed out? (IE: Flushed)
When this condition occures, can you pump the pedal and recover some of the pedal stiffness?

Can you thick of any other observations you've noticed?

P

 

Thanks for the replies, and yes P_Adams, I'd agree 100% that the brakes would get harder when the A/C is on. As for brakes being flushed, I bought the car as the 2nd owner and I never did anything with the brake system, so that will have to get checked out. I can pump the brakes to get some stiffness back, but they are still spongy. If I turn off the A/C, the brakes seem a little better, but they are still soft. I've read some other threads that bad master cylinders/air in lines, etc. tend to appear more in hot weather, so it just may be coincidence....that is, it's hot and the brakes are acting up, and because it's hot, I have the A/C on.

 

Actually, mine do the same exact thing as yours mostly. If it is hot at outside at all, or the car runs for a while when it is warm outside, it gets very spongy and all, but no leaking fluid or anything. Asked the brakes teacher at my school and he said it sounds like the fluid was boiling, and to at least flush and replace fluid if not flushing and replacing with a higher boiling point fluid. This of course should only be done after all leaks are checked for and all that.

 

It's acting (without the heat factor) like the system has either air in it, or the master cylinder may have a bad spot developing.
I know this is going to sound gross, but stick your finger in the master cylinder reservoir and scrap the bottom. If the fluid is cloudy brown and you get a brown paste from the bottom then I would suggest:
1) Power flush the brake system
2) Anticipate replacing the Master Cylinder.

The brake fluid absorbs water of the course of time and when it becomes saturated, the water starts pooling - rusting cylinder wall.

P

 

I know this an Old thread But i plan on checking this, I made a thread about 2 yrs ago and my Master was bad i changed it Now Again my Brakes are Starting To fade, and get soft Pads are Great, No leaks i can See.... Its eather Fluid or master AGAIN..... GRRR DAM ACCORD... LOL

Thanks for the Good info!!!