[Kdogg05]

On my 05 Silverado my brakes feel spongy and the reservoir level keeps going down but there are absolutely no leaks. Could this be my master cylinder is shot? Thanks in advance.

 

[Conlan Rose]

Maybe the master cylinder, could also be a leaky caliper or rear brake cylinder/caliper. You should check all the brake components for leaks.

Link to my thread when my brakes were going out it has some helpful info from other members:
http://www.gmtruckclub.com/forum/showthread.php/130124-Brakes-what-brakes

 

[Pikey]

On my 05 Silverado my brakes feel spongy and the reservoir level keeps going down but there are absolutely no leaks. Could this be my master cylinder is shot? Thanks in advance.

There has to be a leak somewhere if the fluid is going down. It is not magically disappearing. You need to do what Conlan said and check everything. It could be leaking thru the master cylinder and into the brake booster. If that is the case you should see fluid if you look under your dash where the rod goes from your bake pedal thru your firewall.

 

[stchman]

From what I have read brake fluid does not evaporate, so if the fluid level is dropping, you have a leak.

 

[j cat]

On my 05 Silverado my brakes feel spongy and the reservoir level keeps going down but there are absolutely no leaks. Could this be my master cylinder is shot? Thanks in advance.

this mysterious loss of brake fluid and soft spongy brakes is from a leak. this leak could be the line running to the rear brakes on / along the frame rail next to the fuel tank. some have this line leak every 3-4 yrs in the rust belt in this area. the brake fluid will evaporate if the leak is small . this I have seen before. the brake lines get pin holes and leak slowly.

now on the booster any leak with the booster will cause a hard pedal.

pedal to the floor is usually the master is bad.