My brakes make a hissing/air noise when depressing the brake pedal. Also the brakes are almost no exsistent.
I am pretty sure it is the Master Cylinder but someone was telling me could be a vacumm switch?
Any ideas before I by a new master cylinder?
NO leaks...fluid level fine.
This noise is caused by a defective power brake vacuum booster, (big round thing behind the master cylinder) the diaphragm is leaking vacuum.
Actually it sounds like the vacuum booster,which would explain the hissing noise.You easily check this,with the truck running depress the brake pedal and feel for air movement around the actuator rod that comes through the firewall and connects to the brake pedal.Fluid leaks either in the cab or around the master cylinder are generally the first sign that a master cylinder has gone bad.
SOURCE: Air/Hissing Noise from Brake Pedal
air may have gotten into your brake lines. try bleeding your brakes. this will require two people
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