so what the f is wrong with my car

[1969Stang]

okay one of the mechanics installed a new master cyl. on my buick. we did new brakes on it too....so now your caught up. and brake fluid is not a reactent to temp. right?

when i start the car up at say 1 pm on a normal cali day. the brake pedal is normal right... but say i close at work frost on the car or just normal cold. brake pedal is spongy. almost goes to the floor before anything happens....have to drive it on the freeway and use the brakes before anything happens.....brake fluid is fine...not low.all new fluid....we gravity bleed it at work so it has all new fluid...any ideas on what it could be...i'm lost.

oh and on a few occations no matter what its like outside...could be 100 degrees it does it.....not for long...but it still does it. and some times it doesn't go away. i can't figure it out....and its pissing me off....probablys some thing simple(i hope atleast)

[Sluttypatton]

Had the container of brake fluid been opened prior to use? In other words, had the container been left open for any extended periods of time?

[1969Stang]

it was some left over that one of the mechanics had laying around....so yeah...think something could of contaminated it?

[Sluttypatton]

If brake fluid is left open to the air for extended periods of time it will absorb moisture, making it compressable. Usually this is far more noticeable as the fluid heats up. The spongyness of the pedal will depend on how water logged the fluid is.
Whether or not this is the cause of your troubles, I can't say for sure, but it sounds like there is something wrong with the fluid because it is compressable.
Try changing the fluid with brand new brake fluid from a unopened container (make sure it is the same DOT rating as the last fluid). This is pretty cheap, so if it doesn't fix the problem you haven't lost much. Make sure to properly bleed the brake lines.

[burly]

Also to be aware of, if you get air in the lines it can have a similar effect. As the car sits for longer periods of time, the air bubbles can "collect", sort of like when bubbles in a soda bottle go to the top and "collect" as one large air bubble, magnifying it's effect.. While the brake fluid itself shouldn't be affected by the change in temperature, the air (and moisture, as Sluttypatton suggested) is affected. When the car is cold, the air (and moisture) will contract, adding more play to the pedal. When the fluid becomes warmer, the air (and moisture) will expand, providing more pressure in the system. Not only does this provide a diminished level of braking performance, but it can also reek havoc on an ABS system. I recommend the same course of action as Sluttypatton.

[1969Stang]

both of ya.....thanks....i'll do it when its not raining......