Air brake test

[TXBart]

Part of the Texas DMV air brake test directs to shut down the engine then turn the key back on and depress the brake pedal. Air pressure should not decrease more than 3 psi. Mine decreases about 20-30 psi. I realize it is not a commercial vehicle with a large air tank but I am taking my non-CDL Class B driving test tomorrow. Is there another explanation other than this is not a commercial vehicle with a large air tank? I don't want to fail the test before I hit the road because I, or the evaluator, do not understand our air brake system or can't explain it.

This afternoon was the first time I have done the air brake test on my Entegra, or any other vehicle as far as that goes.

Thanks!

[Mac99]

IMHO, you have a serious problem with an air leak in the system.
This is why the test is conducted.

[chlrman]

Tx Bart had you set and released park brake or not? I would set it and then shut down engine. Then turn key back on and do the pedal test, not taking the park brake off because that consumes allot of air to re pressurize the emergency brake system. Good luck on test.
Robert

[johnnyreno]

Don't press the brake very hard just make it look like you are...... JUST SAYIN.

[Twomed]

IF you are doing the test per the book you have a very dangerous issue, size of air tanks does not matter.

IF the examiner watches over your shoulder as they should, your test will be over.

IF that was a commercial vehicle it would be out of service on the spot.

Check that you are doing the test correctly again, if yes and you have that big of a leak call Spartan or CS. They will probably tell you not to drive it and help you get it fixed before you move it.

Class A CDL Air Brake Test Texas TX - YouTube

5.3.3 - Step 7 Final Air Brake Check

Figure 5-5

Do the following checks instead of the hydraulic brake check shown in Section 2, Step 7: Check Brake System.
Test Low Pressure Warning Signal. Shut the engine off when you have enough air pressure so that the low pressure warning signal is not on. Turn the electrical power on and step on and off the brake pedal to reduce air tank pressure. The low air pressure warning signal must come on before the pressure drops to less than 60 psi in the air tank (or tank with the lowest air pressure, in dual air systems). See Figure 5.5.
If the warning signal doesn't work, you could lose air pressure and you would not know it. This could cause sudden emergency braking in a single-circuit air system. In dual systems the stopping distance will be increased. Only limited braking can be done before the spring brakes come on.
Check Spring Brakes Come On Automatically. Continue to fan off the air pressure by stepping on and off the brake pedal to reduce tank pressure. The tractor protection valve and parking brake valve should close (pop out) on a tractor-trailer combination vehicle and the parking brake valve should close (pop out) on other combination and single vehicle types when the air pressure falls to the manufacturer's specification (20 - 40 psi). This will cause the spring brakes to come on.
Check Rate of Air Pressure Buildup.When the engine is at operating rpms, the pressure should build from 85 to 100 psi within 45 seconds in dual air systems. (If the vehicle has larger than minimum air tanks, the buildup time can be longer and still be safe. Check the manufacturer's specifications.) In single air systems (pre-1975), typical requirements are pressure buildup from 50 to 90 psi within 3 minutes with the engine at an idle speed of 600-900 rpms.
If air pressure does not build up fast enough, your pressure may drop too low during driving, requiring an emergency stop. Don't drive until you get the problem fixed.
Test Air Leakage Rate.With a fully-charged air system (typically 125 psi), turn off the engine, release the parking brake, and time the air pressure drop. The loss rate should be less than two psi in one minute for single vehicles and less than three psi in one minute for combination vehicles. Then apply 90 psi or more with the brake pedal. After the initial pressure drop, if the air pressure falls more than three psi in one minute for single vehicles (more than four psi for combination vehicles), the air loss rate is too much. Check for air leaks and fix before driving the vehicle. Otherwise, you could lose your brakes while driving.
Check Air Compressor Governor Cut-in and Cut-out Pressures.Pumping by the air compressor should start at about 100 psi and stop at about 125 psi. (Check manufacturer's specifications.) Run the engine at a fast idle. The air governor should cut-out the air compressor at about the manufacturer's specified pressure. The air pressure shown by your gauge(s) will stop rising. With the engine idling, step on and off the brake to reduce the air tank pressure. The compressor should cut-in at about the manufacturer's specified cut-in pressure. The pressure should begin to rise.
If the air governor does not work as described above, it may need to be fixed. A governor that does not work properly may not keep enough air pressure for safe driving.
Test Parking Brake. Stop the vehicle, put the parking brake on, and gently pull against it in a low gear to test that the parking brake will hold.
Test Service Brakes.Wait for normal air pressure, release the parking brake, move the vehicle forward slowly (about five mph), and apply the brakes firmly using the brake pedal. Note any vehicle "pulling" to one side, unusual feel, or delayed stopping action.
This test may show you problems, which you otherwise wouldn't know about until you needed the brakes on the road

If you have air brakes it is your responsibility to check them daily/ before driving off. If they fail it could get very exciting or expensive.

Hope this helps.

[texnet]

When I took my Texas non-CDL test the examiner set in the passenger and told me what to do and ask what the readings were. I wouldn't call what I did as a test as she guided me through each step!

[brobox]

I just added the air brake check list to my delivery check list. I had an air leak when I got the TS, but it was in the air ride. However they can and do have leaks from the factory. Thanks for that post.

[brobox]

Vance, I just read the air brake test that Twomed posted...I would really be concerned if your MH failed the test more about brake safety than the State test. Check to make sure you are doing the test correctly, that does sound very high for pressure loss.

I test my brakes and air system before our annual long trip each year and about 3 PSI is normal on mine when I apply the brakes, and recovery is almost instant. Until last year...on the air ride side I found that the ride height valve had split wide open. That could have been a brake fitting just as easy. Replaced the valve before the trip and no surprises leaving us along side the road.

I have had two major air leaks, thankfully they have both been on the ride side and not the brake side of the air system.
Test Air Leakage Rate.With a fully-charged air system (typically 125 psi), turn off the engine, release the parking brake, and time the air pressure drop. The loss rate should be less than two psi in one minute for single vehicles and less than three psi in one minute for combination vehicles. Then apply 90 psi or more with the brake pedal. After the initial pressure drop, if the air pressure falls more than three psi in one minute for single vehicles (more than four psi for combination vehicles), the air loss rate is too much. Check for air leaks and fix before driving the vehicle. Otherwise, you could lose your brakes while driving.

[TXBart]

Key to my concern is "after the initial drop." When I press the pedal pressure drops about 20 psi but holds "after the initial drop." It also drops about 20 psi from running to off then key back on, so did the truck in the video.

I don't think my brakes have an issue, I guess I will confirm that at 8:30.

[ShadowBolt]

Originally Posted by TXBart

Key to my concern is "after the initial drop." When I press the pedal pressure drops about 20 psi but holds "after the initial drop." It also drops about 20 psi from running to off then key back on, so did the truck in the video.

I don't think my brakes have an issue, I guess I will confirm that at 8:30.

How much pressure does your Entegra hold? I keep reading most vehicles it is 125 psi. My coach holds about 135 on the left (front) gauge and 145 on the right (rear) gauge. Maybe the gauges are not accurate but that's what mine show. I would like to hear from others before I bother Scott with an e-mail.


JJ

[Dogpatch]

Originally Posted by Twomed

IF you are doing the test per the book you have a very dangerous issue, size of air tanks does not matter.

If you have air brakes it is your responsibility to check them daily/ before driving off. If they fail it could get very exciting or expensive.

Excellent info Twomed! That's the way I learned it! Bet most people don't know it!

[Dogpatch]

Originally Posted by ShadowBolt

How much pressure does your Entegra hold? I keep reading most vehicles it is 125 psi. My coach holds about 135 on the left (front) gauge and 145 on the right (rear) gauge. Maybe the gauges are not accurate but that's what mine show. I would like to hear from others before I bother Scott with an e-mail.


JJ

It may differ from one manufacturer to another. The key is to ensure you have enough air to operate the system. Minimum I believe is 115 psi but most operate as said at 125.

If you are running at those pressures, it may be a governor issue. I would check with your manufacturer.

[brobox]

Originally Posted by ShadowBolt

How much pressure does your Entegra hold? I keep reading most vehicles it is 125 psi. My coach holds about 135 on the left (front) gauge and 145 on the right (rear) gauge. Maybe the gauges are not accurate but that's what mine show. I would like to hear from others before I bother Scott with an e-mail.


JJ

This is the second or third time I have seen posted that Entegra air gauges will read as high as 150 lbs. I am scratching my head on this as the air valves are suppose to bleed off at 125 PSI. The air valve on my Spartan Chassis was installed by Spartan and it's dead on at 125 PSI on both gauges.

Who installes the Gauges on the Entegra's? And are others having high air pressure readings?

To much air pressure is not good, the ride height valves are plastic and they will split with too much air pressure. Heck, they split without too much air pressure

[thrushl]

Originally Posted by macadnphyl

IMHO, you have a serious problem with an air leak in the system.
This is why the test is conducted.

x2!!! My humble friendly recommendation is that you find a heavy truck repair shop and get that checked before your next trip. Just saying....