• Air brakes lag and seize when they need to be adjusted.brake calipers image by Tom Oliveira from Fotolia.com
  
  Air brakes act very much like the hydraulic brakes used in many automobiles, except instead of using a hydraulic fluid, they use compressed air. Air brakes are used most often on large trucks or other heavy vehicles, where air braking is more efficient than hydraulic braking. Owners of smaller automobiles can also choose to install air brakes. Air brakes can shift over time, and must be checked and adjusted to keep them operating properly.
  
  

Increased Lag

• When an air brake starts slipping, the piston that moves back and forth in response to air pressure needs to move further and harder to exert the same amount of force. As a result, the air brake loses efficiently and lags, taking time to stop the wheels of the automobile. If a lag time starts to grow between using the brake and the automobile stopping, then it may be time for an adjustment.
  
  

Loss of Control

• If you are driving an automobile that uses air brakes and you try to brake, you may notice a slight loss of control. Sometimes, one or more of your tires will seize up. This is caused by badly aligned air brakes that are either not working at all or freezing due to lack of compression. This is a definite sign that the brakes need attention.
  
  

Worn Linings

• When air brakes are misaligned, the angle of force that operates the push rod (the primary piston in each braking unit) increases, creating a friction problem that wears away at the lining next to the brake drum. If your linings are worn or making noise, this is another sign that you need to adjust your brakes.
  
  

Measurement

• Most air brakes come with markers on the push rod that show where it is supposed to be at its extended and contracted positions. If you turn off your vehicle, leaving the transmission in low gear, you can push and pull the push rod yourself to see how far it extends. If the rod extends past its markers, it needs to be readjusted to provide the proper amount of force.