Does ABS Work If Emergency Brakes Come On?

Topic 26753 | Page 1

Page 1 of 2 Next Page Go To Page:
Amber L.'s Comment
member avatar

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.

Jamie's Comment
member avatar

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

Errol V.'s Comment
member avatar

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.

Tandem:

Tandem Axles

A set of axles spaced close together, legally defined as more than 40 and less than 96 inches apart by the USDOT. Drivers tend to refer to the tandem axles on their trailer as just "tandems". You might hear a driver say, "I'm 400 pounds overweight on my tandems", referring to his trailer tandems, not his tractor tandems. Tractor tandems are generally just referred to as "drives" which is short for "drive axles".

OWI:

Operating While Intoxicated

Amber L.'s Comment
member avatar

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.

Tandem:

Tandem Axles

A set of axles spaced close together, legally defined as more than 40 and less than 96 inches apart by the USDOT. Drivers tend to refer to the tandem axles on their trailer as just "tandems". You might hear a driver say, "I'm 400 pounds overweight on my tandems", referring to his trailer tandems, not his tractor tandems. Tractor tandems are generally just referred to as "drives" which is short for "drive axles".

OWI:

Operating While Intoxicated

Errol V.'s Comment
member avatar

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 L.'s Comment
member avatar
Amber plays "the foot bone is connected to the pedal bone, the pedal bone is connected to the air regulator" game:

rofl-2.gifrofl-2.gif 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

Errol V.'s Comment
member avatar

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.

CDL:

Commercial Driver's License (CDL)

A CDL is required to drive any of the following vehicles:

  • Any combination of vehicles with a gross combined weight rating (GCWR) of 26,001 or more pounds, providing the gross vehicle weight rating (GVWR) of the vehicle being towed is in excess of 10,000 pounds.
  • Any single vehicle with a GVWR of 26,001 or more pounds, or any such vehicle towing another not in excess of 10,000 pounds.
  • Any vehicle, regardless of size, designed to transport 16 or more persons, including the driver.
  • Any vehicle required by federal regulations to be placarded while transporting hazardous materials.

Combination Vehicle:

A vehicle with two separate parts - the power unit (tractor) and the trailer. Tractor-trailers are considered combination vehicles.

HOS:

Hours Of Service

HOS refers to the logbook hours of service regulations.

OWI:

Operating While Intoxicated

Stevo Reno's Comment
member avatar

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

Amber L.'s Comment
member avatar

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!

OOS:

When a violation by either a driver or company is confirmed, an out-of-service order removes either the driver or the vehicle from the roadway until the violation is corrected.

Errol V.'s Comment
member avatar

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.

Page 1 of 2 Next Page Go To Page:

New Reply:

New! Check out our help videos for a better understanding of our forum features

Bold
Italic
Underline
Quote
Photo
Link
Smiley
Links On TruckingTruth


example: TruckingTruth Homepage



example: https://www.truckingtruth.com
Submit
Cancel
Upload New Photo
Please enter a caption of one sentence or less:

Click on any of the buttons below to insert a link to that section of TruckingTruth:

Getting Started In Trucking High Road Training Program Company-Sponsored Training Programs Apply For Company-Sponsored Training Truck Driver's Career Guide Choosing A School Choosing A Company Truck Driving Schools Truck Driving Jobs Apply For Truck Driving Jobs DOT Physical Drug Testing Items To Pack Pre-Hire Letters CDL Practice Tests Trucking Company Reviews Brett's Book Leasing A Truck Pre-Trip Inspection Learn The Logbook Rules Sleep Apnea
Done
Done

0 characters so far - 5,500 maximum allowed.
Submit Preview

Preview:

Submit
Cancel

Join Us!

We have an awesome set of tools that will help you understand the trucking industry and prepare for a great start to your trucking career. Not only that, but everything we offer here at TruckingTruth is 100% free - no strings attached! Sign up now and get instant access to our member's section:
High Road Training Program Logo
  • The High Road Training Program
  • The High Road Article Series
  • The Friendliest Trucker's Forum Ever!
  • Email Updates When New Articles Are Posted

Apply For Paid CDL Training Through TruckingTruth

Did you know you can fill out one quick form here on TruckingTruth and apply to several companies at once for paid CDL training? Seriously! The application only takes one minute. You will speak with recruiters today. There is no obligation whatsoever. Learn more and apply here:

Apply For Paid CDL Training

About Us

TruckingTruth was founded by Brett Aquila (that's me!), a 15 year truck driving veteran, in January 2007. After 15 years on the road I wanted to help people understand the trucking industry and everything that came with the career and lifestyle of an over the road trucker. We'll help you make the right choices and prepare for a great start to your trucking career.

Read More

Becoming A Truck Driver

Becoming A Truck Driver is a dream we've all pondered at some point in our lives. We've all wondered if the adventure and challenges of life on the open road would suit us better than the ordinary day to day lives we've always known. At TruckingTruth we'll help you decide if trucking is right for you and help you get your career off to a great start.

Learn More