Does ABS Work If Emergency Brakes Come On?

So we had this debate in class today.

If you were to ignore the low air warning and continue driving until the emergency brakes come on will the ABS still work or will your wheels just lock up?

Obviously, when you're low air warning device comes on you pull over and stop as soon as safely possible. Just a debate about the mechanics of it.

Your wheels would lock up, since the low air would make the spring brake activate.

Amber, Class is in session.

The tractor drive axles, and the trailer tandem axles have two, TWO air brakes in one! The steer axles have one chamber while the others have two - one stacked on the other.

The two systems work completely independent from each other. The service brakes (your foot pedal) do the slowing and use the Antiskid Braking System. The parking brakes are controlled by the two buttons on the dashboard as well as the low pressure warning system. The parking system does not have ABS.

Class dismissed.

Errol, That is exactly what I was thinking! So to get a little more in-depth of the mechanics, because I'm curious, the service brakes when applied use air pressure to push the diaphragm in the brake chamber which moves the push rod, which moves the slack adjuster, moves the S cam shaft, moves the S cam, pushes the brake shoes against the inside of the drum. So the ABS is essentially a "relief valve" that let's the air pressure out thus letting the brake shoes move away from the brake drum. It can open and close much faster than a person can move their foot on the pedal.

Do I have that right? Thank you!

Amber, Class is in session.

The tractor drive axles, and the trailer tandem axles have two, TWO air brakes in one! The steer axles have one chamber while the others have two - one stacked on the other.

The two systems work completely independent from each other. The service brakes (your foot pedal) do the slowing and use the Antiskid Braking System. The parking brakes are controlled by the two buttons on the dashboard as well as the low pressure warning system. The parking system does not have ABS.

Class dismissed.

Amber plays "the foot bone is connected to the pedal bone, the pedal bone is connected to the air regulator" game:

Errol, That is exactly what I was thinking! So to get a little more in-depth of the mechanics, because I'm curious, the service brakes when applied use air pressure to push the diaphragm in the brake chamber which moves the push rod, which moves the slack adjuster, moves the S cam shaft, moves the S cam, pushes the brake shoes against the inside of the drum. So the ABS is essentially a "relief valve" that let's the air pressure out thus letting the brake shoes move away from the brake drum. It can open and close much faster than a person can move their foot on the pedal.

Close enuff for yer understanding, beyond that, talk to a mechanic. :)

While on the subject of air brakes for someone in class, keep this in mind: The service brakes work when there is pressure, and your foot pedal allows air into the system to push the brake pads onto the rim. (Key point: The service brakes use air pressure to work the brakes)

On the other hand, the Parking and Trailer brakes work when the air pressure is gone. (Key point: The parking/emergency brakes work & stop when there is air NO pressure (gauge reads 0) to set the brakes)

So the yellow and red buttons on the dash actually let out all the pressure in the emergency/parking brake lines (The big chuff you hear when you press the buttons in.). This thing about when having air pressure stops the truck (service brakes) and when no air pressure stops the truck (parking/emergency brakes) can be confusing for new people.

The loud audio alarm and the warning lights go on when the low air pressure warning happens. This is to let the driver know that very soon everything in the cab, including her face, will be thrown toward the windshield without further warning.

Amber plays "the foot bone is connected to the pedal bone, the pedal bone is connected to the air regulator" game:

Thanks again! I know it's not essential knowledge just a darn curious person! I feel like I'm doing pretty good on understanding the basics of the truck.

I really don't like that the air supply knob can be called the tractor protection valve. Because knob isn't added to the end, I would be fine with tractor protection valve knob because it's a darn knob not a valve....the knob controls the valve but it is still a darn knob.

Took me forever to keep that straight and it makes for some seriously tricky questions on the test.

Sorry that was a little rant

Rants are OK. And I'm taking the time to tell you these things because knowing about the brake systems IS important for a new driver. You will be bleeding out the air from the system during the pretrip and explaining to the examiner what's going on. (Chill - just wait for the class on what I really mean.)

Those two "buttons" we're talking about are really valves. The valve parts are just inside the dashboard where the air lines come to be "valved". And you'd better look up why the tractor protection valve is called that.You might need to know it for your Permit test if you still need to do that. I'll make it easy. here's section 6.2 in the manual: Combination Vehicle Air Brakes

I'm not trying to get on your case, but I do want you to know this stuff come test time.

P.S. air brakes work same as your cars prevents wheels from. Locking up n skidding

Hey Errol, I asked this question originally because one of the teachers said the ABS would work if the emergency brakes came on but I didn't understand how the ABS could work in that situation. So I hoped someone could explain why it could or couldn't happen to me more clearly.

I do understand why it's called the tractor protection valve, just makes for some tricky questions ( stops/protects the tractor from loosing air if there is an air leak in the trailer air system eg. the emergency air line gets disconnected) I can't seem to find any right now but I know at first I was getting really confused as to what they were talking about in some questions but through asking some questions in class I got that straighten out.

Thank you for your time and support!

Amber searches for meaning:

I can't seem to find any [tractor protection valve questions] right now

They are there. The list of air brake questions include several asking what happens when the trailer air lines get disconnected.