brakes
 

I have a 77 blazer 4x4 w/ disc brakes and lately when I press on the brake pedal it makes a hissing noise and if I tap the brakes the pedal will go down a little bit on its own. I'm thinking maybe I just need to check the brake fluid level but if that isn't the problem what could be causing this?

The gasket between the cover and the master cylinder might have a pin hole in it that is letting air into the system. If that isn't it then the brake lines running from the proportioning valve could be leaking too.

Definitely air in the system just completed changing a bad wheel cylinder in my camaro with the hissing when you pushed the pedal.

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79 chevy blazer frame with 79 cab cut down 77 stepside bed 38.5 boggers.