7 step air brake test

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What is the 7 Step Air Brake Test

In-cab air brake test is 7 Step Air Brake Test that is mandatory in tractor-trailer inspection. Tractor trailer inspection is compulsory for professional drivers in every 24 hours. CDL 7 Step Air Brake Test to be performed in the cab before taking a commercial vehicle to a public road.

How to do the Step Air Brake Test

There is a Step Air Brake Test sequence. You will not miss anything following this. This sequence is easy to remember with the word LAGGASS. Where :

  •  L for Low Air Warning Device.
  •  A for Air Pressure Buildup.
  • G for Governor Cut Out.
  • G for Governor Cut In.
  • A for Air Loss Rate.
  • S for Spring Brake Test.
  • S for Service Brake Test.

These are in cab air brake checks. Step by step procedure is to perform 7 Step Air Brake Test is as follows.

What is Low Air Warning device test?

It is the testing of an audible and visible signal on the dashboard of your vehicle. The low air warning device is working if it activates on or before 55psi.

How to test a low air warning device?

Apply the wheel chocks.

Make sure your air pressure is over 90psi.

Pump down the brake pedal and watch the needles on the dashboard.

The audible and or visible indication must activate on or above 55 psi.

Example wording for the Low air Warning Device Test

“I am testing my low air warning device now, the device must activate on or before 55psi, if it does not activate, the vehicle fails the test, and I will mark it out of service.

Now my low air warning device activates at_____psi(must be on or over 55psi). so it is a pass.”

Why the low air warning device test is important?

The low air warning device warns the professional driver to pull out safely whenever air pressure drops below 55psi.

Automatic application of spring brakes is also linked with the low air warning device. If you continue losing air and the device does not activate, the air brake system applies spring brakes to stop the vehicle.

So it is a big safety feature of the air brake system works before the vehicle loses stopping ability.

What is air pressure buildup test?

Air pressure build-up test is the test of air compressure. The air compressure must work properly to keep enough air tanks. The air pressure should build up from 85 to 100 psi within 2 minutes engine running at 600 to 900rpm.

How to test air pressure buildup?

Make sure engine running at 600 to 900rpm.

Since you already pumped down the pressure to 55psi in the previous test, no need to pump down again.

Watch the needles moving 85psi to 100psi within 2 minutes.

Example wording for the Air Pressure Buildup Test

“I am testing air pressure buildup, watching my needles and time.

the air pressure must build up from 85psi to 100psi within 2 minutes engine running at 600 to 900rpm. I will mark the vehicle out of service if it fails to build up.

It is a pass because of air pressure build-up from 85psi to 100psi within 2 minutes.”

Why the air pressure buildup test is important?

We lose air whenever use brakes, the compressor should fill up required air within time frame keeping us always in normal operating range while the vehicle is in operation.

What is Governor cut out?

The governor cut out is when air compressure stops pushing air into the tanks. We hear a “thhhhisssss” sound when cut out occurs.

The minimum rock bottom cut out is 100psi and maximum cut out is 145psi.

How to test the governor cut out?

Watch the needles moving.

Open the driver window to hear the cut-out sound.

Example wording for the Governor cut out Test

“I am testing governor cut out now, watching needles and waiting to hear the cutout sound. If the governor does not cut out at 145psi, it is fail and I will mark the vehicle out of service.

So now it is pass because needles stopped moving and I hear cut out sound at _________psi.”

Why the governor cut out test is important?

The air brake system may be damaged if the governor does not cut out. The safety feature here is the safety valve located on air tanks. It will open and drain air tanks when the pressure reaches 150psi.

What is governor cut in test?

Governor cut in is when the air compressor starts pushing air into air tanks. It is 20 to 25psi less than the cut out pressure.

Rock bottom cut in is 80 psi.

How to test the governor cut in?

Pump down brakes 20psi to 25psi less than cut out pressure.

Watch the needles to start moving.

Pump down 5psi more if needles do not start moving.

Example wording for the Governor cut in Test

“I am testing governor cut in now, watching needles to move after pumping down 20psi lower than the cut-out pressure, It will fail if it does not cut in on 80psi.

So no it is pass because my needles started moving and cut in is _________psi.”

So my Normal Operating Range is______to____psi.

Why the governor cut in test is important?

You will run out of the air if the governor does not cut in.

What is the air loss rate test?

The air loss rate is the test of air leakage from the air brake system. Your vehicle should not lose more than 3psi(straight truck, coach bus, school bus), 4psi(a tractor-trailer) and 6psi(tractor and two trailers) in one minute.

How to test the air loss rate?

Make sure the vehicle is parked on a level surface.

Air pressure is in normal operating range.

Apply wheel chocks.

Turn off the engine.

Release the spring brakes and apply and hold service brakes for one minute.

Open windows to listen to the air leakage

Example wording for the Air loss rate test

“I am testing air loss rate now, watching time for one minute and listening for air leakage, It should not lose more than 3psi after an intial loss in one minute. if I lose more then 3psi(say this according to vehicle) within a minute, it will fail the test, otherwise, it is a pass.

Now my vehicle has passed the air loss rate test.”

Why the air loss rate test is important?

The air brake system will run out of the air and unable to stop the vehicle if the loss is more than the specified range.

What is the service brake test?

Service brake test is the examination of the vehicle`s stopping ability.

How to test the service brakes?

service brakes, brake pedal
service brakes/ brake pedal

Apply the spring brakes.

Remove wheel chocks.

Now release the spring brakes and put the vehicle in transmission.

Accelerate gently and apply service(brake padel) brakes.

If your brakes hold your vehicle smoothly in parallel then your service brakes are working.

Example wording for the service brake test

“I am testing service brakes now, my vehicle stops smoothly and in parallel, so it is a pass.

It is a fail and I will mark it out of service if it does not stop smoothly and in parallel.”

Why the service brake test is important?

Your vehicle must stop in parallel and smoothly whenever needed. if it pulls to any side, one of your brakes might be out of adjustment.

What is Spring Brake Test?

It is the testing of the vehicle`s parking brakes.

How to test the service brakes?

tractor trailer spring brakes
tractor trailer spring/parking brakes

Put the vehicle in transmission.

Role couple of feet gently and apply the spring brakes.

Spring brakes must hold the vehicle smoothly in parallel.

Example wording for the spring brake test

“I am testing spring brakes now, my vehicle stops smoothly and in parallel, so it is a pass.

It is a fail and I will mark it out of service if it does not stop smoothly and in parallel.”

Why the spring brake test is important?

Spring brakes are used to park the vehicle, so your vehicle must need it.

Remember, spring brakes automatically start applying when the air pressure drops to 50psi.

Next steps in air brake testing are…

1. Draining of air tanks.

2. Pushrod measurement.

You can find both in

https://www.truckservicez.com/blog/brake-adjustment-introduction/

Download 7 step air brake test pdf here

Tractor trailer inspection

CDL 7 Step Air Brake Test video https://www.youtube.com/watch?v=dHDNrwbeyyw&t=322s

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