Hissing brake chamber

Anything made out of rubber will fail. Actually braking you are relieving air pressure. It's normal wear and tear.

 

It happens. A "hard braking" should not be considered a possible cause for one's failure. Some times they're borderline, and the first cold snap can cause them to fail.

 

There are different designs but this diagram gives you a general idea. The diaphragm can crack, rupture or break seal. That goes for anything that is air (vacuum) actuated.

 

Typically, if a diaphragm ruptures or leaks, that hissing noise will often be accompanied by a flow of air from one of the vent holes in the brake chamber's housing. There doesn't have to be a crack in the chamber.

If it's a small leak, the flow will be very very slight, sometimes almost undetectable. You have to get right next to the diaphragm and feel the vent hole to tell.
Other times, with a larger diaphragm (pancake) leak, the air will be gushing out the vent hole.

Plus, it depends on which diaphragm is leaking (service side or emergency side). You can't detect a service side leak until the brake pedal is pushed (or johnson bar for trailer). A standard pre-trip air pressure systems check will tell if you have any air loss, or abnormalities, in the brake system (other than mechanical defects, such as brakes out of adjustment, etc).

Also, what commonly is bad for blowing diaphragms is when you apply your spring brakes (yellow/red knobs pulled) and then apply pressure to your brake pedal. This causes a pressure "overload" to the diaphragm, due to both spring force plus air pressure force.

 

That's good advice I forgot. Don't sit in the drivers seat and play with the brake pedal while your buttons are popped. Many of your newer trucks have protection valves built in but never get in this practice because you don't know what you have.

 

Dang!.... and I was just perfecting my "air drum" rendition of In-A-Gadda-Da-Vida...

 

just go get it fixed, this week is truck DOT wright em up week.

 

True. It's either one or the other (brake pedal/knobs in OR knobs out/NO brake pedal).
I actually hate to refer to them as red/yellow knobs (but sometimes do for newbie "simplicity"), and rather prefer new students learn them by their proper name, service and emergency popout valves.

I'm not aware about protection valves on newer trucks (that prevent spring/air overload, as mentioned).
All trucks should be (are) equipped with a tractor protection valve, but that won't protect from overpressure, due to knobs being out while pedal is depressed.
The tractor protection valve is usually mounted behind the cab, or on the firewall, and detects sudden significant imbalances in the air system (such as by large air leak, blown hose, or gladhand coming undone). When/if this happens, the tractor protection valve will automatically flip to the shut position and prevent air loss beyond the tractor, so the tractor will retain enough air pressure reserve for "short-term" adequate braking.

I once had a service glad hand pop off in transit, on a truck that I had written up everyday for 2+ months (popout valves failed to popout on systems check and had signs the tractor protection valve was questionable). Results were.. when I was approaching a toll gate, I depressed the brake pedal, and I watched my air pressure dump completely out within seconds. Pressure dropped like a rock. I had almost no braking effect at all for the majority of the distance (like dragging a stick), until the spring brakes barely coasted me to a stop, once air was virtually at 0 psi.

A stuck/bad tractor protection valve nearly cost me a collision.
And yes, I was to blame for driving that truck with a known problem, tho my company refused to fix.
If had to do it all over again, I'd certainly refuse to have driven it, until fixed.