Air Brake Lesson Main Parts A. Air Compressor- Pumps air into the storage tanks(5-1) B. Air Governor- Tell the compressor when air is pumped into the tanks(5-1) C. Air Storage Tanks- Stores compressed air for regular use during braking(5-1) D. Dual Parking Control Valve- Permits you to release the emergency brake to move a short distance.(5-4) E. Dual Air Brakes- Has two separate air brake systems which use a single set of brake controls. If one system is very low on air pressure, either the front or rear brakes will not be operating fully. Bring vehicle to a stop.(5-5) Dual Air Brakes Air Compressor Air Governor Air Tank Extra Tank Primary Secondary Maintenance Dual Parking Control Valve Air Storage Tanks- Drain Every day, because water can freeze in cold weather and cause brake failure.(5-1) Alcohol Evaporator- Check level every day because it helps reduce the risk of ice in the brake valves during cold weather.(5-2) Gauges Supply Pressure Gauge Application Gauge Supply Pressure gauges- (5-2) Must be in all vehicles that have air brakes. They monitor how much air is in the air tanks. Application Gauge (5-3) Tells you know how much air pressure if being applied as you press the service brake. Not all vehicles are equipped with application gauges.
PSI CHART 150- Safety Valve- Protects the tank and the rest of the system from too much pressure(5-2) 125- Governor Cut- Out- Stops the compressor from pumping air(5-1) 100- Governor Cut-In- Allows the compressor to start pumping air(5-1) 60- Low Air pressure warning light- Warning signal and buzzer comes on before air pressure in (5-3) the tank fall to 60 psi. Bring the vehicle to a safe stop. 45- Spring Brake (20-45psi)- Activates after low air pressure warning light at 20-45 psi. 20-(5-3)&(5-7) Air pressure Build-up-the air pressure should build from 85-100 psi in 45 seconds.(5-7) Types of Brakes 1. Service Brake = Brake Pedal (5-2) a. Stop light switch (tail lights). Helps warn drivers behind you that you are stopping. (5-3) b. Pressing repeatedly can let air out faster than the compressor can replace. (5-2) c. Front wheel braking in good under all conditions.(5-3) 2. Parking Brake- Requires Air pressure to work, and must be on at all times whenever you park or leave the vehicle.(5-3) 3. Emergency Brake = Spring Brake. Works without air pressure. Activates at 20-45 Psi. (5-3) Comes on when you loose air pressure Held by mechanical force when air is low or gone. Held by powerful springs Does not leak air While driving in normal conditions, they are held back by air pressure Never push the service brake and the spring brake at the same time, they can be damaged by the combined forces The braking power depend on brakes being in adjustment 4. Front Brake limiting valve- Vehicles older than 1975. They reduce the chance of a front wheel skid(5-3)
Brakes Parts S-cam They are the most common type (foundation brakes). (5-2) 1. Air pressure pushes the rod out and the Scam forces the brake shoes against the inside of the brake drum. Brake Drum- Should not have cracks more than ½ inch of the friction area. (5-6) Brake Shoes- (5-2) Air Leakage Test (5-7) Too much heat may cause them to stop working (5-2) Must not be worn dangerously thin (5-6) Must not have oil or grease on them They are pushed against the inside of the brake drums Test 1- With the foot OFF the brake pedal Must have aprox 125 psi Turn of Engine Count for 1 minute o Single- Less than 2 Psi/1 Min o Combination- Less than 3 Psi/1Min Test 2- With the foot ON the brake pedal. Service Brake Test (5-7) Must have aprox 125 psi Turn of Engine Chock Wheels Apply your foot to Service Brake Count for 1 minute o Single- Less than 3 Psi/1 Min o Combination- Less than 4 Psi/1Min Wait for normal air pressure to build Move vehicle slowly 5-10 MPH Apply brakes firmly Vehicle should not pull to one side
Slack Adjustor Test(5-6) Park on level ground Chock the wheels s Use gloves and pull hard The slack adjuster should not move more than one inch Emergency Stops (5-8) Controlled Braking- You apply the brakes as hard as you can without locking the wheels. Stab Braking- Apply your brakes all the way. Release the brakes when wheels lock up. As soon as they start rolling, repeat. * Not recommended with vehicles with ABS brakes. Braking Techniques You should brake in a way that will keep your vehicle in a straight line and allow you to turn if necessary (5-8) The use of the brakes on a long or steep downgrade is only a supplement to the braking effect of the engine (5-9) Apply the brakes hard enough to feel a definite slowdown (5-9) When your speed has been reduced to approx. 5mph below your safe speed release the brakes (5-9) Total Stopping Distance (5-9) Calculating total stopping distance Perception- From the time your eyes see the hazard until your brain recognizes it. Reaction-Before you physically hit the brakes. Brake Lag = Takes longer to flow through the lines than hydraulic brakes. The air brake lag distance at 55 mph on dry pavement adds about 32 feet Stopping Distance -The distance you travel while you are braking. Total Stopping Distance = at 55 mph for an average driver under good traction and brake conditions, the total stopping distance is over 450 or the length of a football field. Brake Fade or Fail (5-9) Caused by excessive heat when used too much Not using the braking effect of the engine Affected by brakes being out of adjustment Expansion of the brake drums
ABS (5-4) & (5-8) Avoids wheel lock up Brake the same way If ABS malfunctions you still have your regular brakes How to check If you have ABS Yellow Abs malfunction lamp Date- March 1, 1997 & 1998 ECU- Electronic Control Unit. Look under the vehicle