2000 Chrysler Concorde LX 2.7 Brake hissing
 

Ok so when it starts to get cold i noticed that when I press down the brakes and hold it there is a hissing noise "Tsssssss" lol... it continues until I release the brakes. On even colder days the break completely bottoms out and does not engage. after a few pumps the break pressure comes back to the peddle and I am able to stop as usual. does any one know what this may be due to, or has had this issue and repaired it. I am not affraid to get my hands dirty just would like to know what I am trying to fix so i am not buying stuff I dont need. any help would be great. Thanks in advance.

Power booster has failed. Hissing noise is a failed diaphragm internal to the booster unit. Note internal pushrod length when you replace it. Most reman units are pre set, some need to be adjusted to match the original unit removed.

OK cool, is that also the reason the pedal bottoms out on cold days as well...?