2005 Model Commercial Driver’s License Manual  5.4.8 – Parking Brakes  Subsection 5.4  Test Your Knowledge  Never leave your vehicle unattended  without applying the parking brakes or  chocking the wheels. Your vehicle might  roll away and cause injury and damage.  Any time you park, use the parking brakes, except  as noted below. Pull the parking brake control  knob out to apply the parking brakes, push it in to  release. The control will be a yellow, diamond- shaped knob labeled "parking brakes" on newer  vehicles. On older vehicles, it may be a round blue  knob or some other shape (including a lever that  swings from side to side or up and down).  Don't use the parking brakes if the brakes are very  hot (from just having come down a steep grade), or  if the brakes are very wet in freezing temperatures.  If they are used while they are very hot, they can  be damaged by the heat. If they are used in  freezing temperatures when the brakes are very  wet, they can freeze so the vehicle cannot move.  Use wheel chocks on a level surface to hold the  vehicle. Let hot brakes cool before using the  parking brakes. If the brakes are wet, use the  brakes lightly while driving in a low gear to heat  and dry them.  If your vehicle does not have automatic air tank  drains, drain your air tanks at the end of each  working day to remove moisture and oil.  Otherwise, the brakes could fail.  These questions may be on your test. If you can’t  answer them all, re-read subsection 5.4.  1. Why should you be in the proper gear before  starting down a hill?  2.  What factors can cause brakes to fade or fail?  3. The use of brakes on a long, steep downgrade  is only a supplement to the braking effect of  the engine. True or False?  4. If you are away from your vehicle only a short  time, you do not need to use the parking  brake. True or False?  5.  How often should you drain air tanks?  6. How do you brake when you drive a tractor- trailer combination with ABS?  7. You still have normal brake functions if your  ABS is not working. True or False?  Section 5 – Air Brakes  Page 5-10 