CDL Test question on brakes

that is the right answer. Brakes are brakes, you are over thinking it

 

Why do they call them "Parking Brakes?" Think about it for a minute. Are you moving or parked?

 

Read the answer again. It doesn't say while coming down a steep grade it says after coming down a steep grade.

 

The others posters are correct, and hopefully you now have a better understanding.
I'll put it another way, just in case you're still unsure.

You ask.. "Parking brakes aren't used when coming down a steep grade. Are they?"

No... BUT many of the same brake parts are used for both systems (parking & service), so technically, yes. But read on for an explanation...
Most of the working/active brake parts, (such as the brake shoes, brake drums, S-cam, and slack adjusters) are the same exact parts in use, whether you are stopped and applying the parking brakes (red/yellow dash valves) OR moving with the service brakes applied (brake pedal). The main parts that get hot are the shoes and drums because of the friction between the shoe and drum, when applied while driving.

So their point is... don't use the parking brake until the brakes cool a bit. If you stopped and applied the parking brake too soon, you are pressing overly hot brake shoes against an overly hot brake drum. Leaving parking brakes NOT applied will allow a small gap between these parts, for quicker brake cooling.

 

First off you should never apply the parking brakes while moving unless it is a dire situation and as far as the brakes going down a grade and being hot well that is more of a circumstance of improper breaking it is called brake fade as a result of riding the brakes and improper enginge retarding and being in the wrong gear

 

I think you are all missing the point. The brake drums expand when hot. Setting the spring brakes with hot drums may cause the drums to crack as they cool off and shrink. The springs may not compress with the cooling drums due to friction at the shoe anchor pins, etc.

 

That makes sense.
To be honest, I had always thought it was to prevent "overcooking" the linings of your shoes by having a red hot brake drum (figuratively, tho they can get RED hot too) tight against/around them.

But the OP's question was also about confusion over brake parts/systems (parking vs service).

 

This is the area of the CDL test that causes people to fail. Study, study and study again.