For both a road test & your daily pre-trip inspection you must determine if the air brakes are in adjustment.

How to Determine Air Brake Adjustment | Air Brake Smart

https://youtu.be/ilo4dNE5ELw

Closed Caption

Introduction

Hi there smart drivers, Rick with Smart Drive Test talking to you today about how to determine that the air brakes are in adjustment.

This is particularly relevant for people getting a CDL license, class 1 or a class 3, D in Ontario...

Any bus or other vehicle that's equipped with air brakes; if you're going for a license, you're going to have to demonstrate how to determine if the air brakes are in fact in adjustment, regardless of the fact that for almost 20 years now we've had automatic slack adjusters on these vehicles.

You still need to determine that, in fact, the air brakes are in adjustment.

There's two methods of doing that and in California ,New York, British Columbia and most of the provinces in Canada, they all use the pry bar method, sometimes called the free stroke.

But most often referred to the pry bar, because you use a pry bar to determine adjustment of the air brake system.

The next one is the applied stroke - in Ontario, Canada I know that they use the applied stroke method.

And if you get pulled into the scale or pulled over by the DOT (Department of Transportation), the CVSE (Commercial Vehicle Safety & Enforcement), the MTO (Ministry of Transportation in Ontario) in Ontario - any one of those diesel bears - they are going to do the applied stroke method.

And the way that they do that is, they put a radio on the door of your vehicle, they go underneath the vehicle and they put a mark at a fixed point on the push rod.

And then they get you to apply the brakes.

They then measure from that fixed point out to the mark that they made on the pushrod.

So today we're going to go over and we're going to show you how to do both the pry bar method and the applied stroke method so that if you get pulled over by the diesel bears, you don't get a fine and you don't end up working the day for free.

And if you're taking a license, you're going to be successful on your license.

Stick around, we'll be right back with that information.

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Hi there smart drivers, welcome back.

Rick with Smart Drive Test talking to you today about how to determine if your air brake system is within adjustment.

If you're going for a license or you get pulled over by the diesel bear--the DOT, the MTO, the CVSE, or any one of those authorities, they're going to check the brakes on your vehicle and ensure that they are within adjustment.

And to determine if they're with an adjustment they're going to use the applied stroke method.

There's two methods that you can use to determine that your air brakes are in fact an adjustment on an air brake equipped vehicle:

1) one is the pry bar;

2) and the other is the applied stroke method.

Safety first on both of these methods, regardless of which one you're using, the first steps of that are two chock the wheels on your vehicle.

Then release the parking brakes and ensure the pressure in the system is above 90 pounds.

Because you need more than 90 pounds in the system to have those powerful spring brakes that apply the parking brakes completely released.

So you need more than 90 pounds (psi - pounds per square inch) in the system - so safety first! Chock the wheels, as you can see here in the image.

Get in the cab, release the parking brakes and put your foot over the service brake just in case the chocks don't hold and the vehicle begins to roll away on you then you're ready in the event that that does occur by applying the service brakes and then ensuring that you have more than 90 psi in the system.

So that's the first step.

For the pry bar method you simply need a pry bar, thus it's called the pry bar method.

You put the pry bar in at the clevis pin and pry out.

And the pushrod should not come out of the brake chamber more than half to three-quarters of an inch.

In the state of California and New York, they both allow you an inch, which is fairly lenient in terms of how much travel is allowed on that push rod, but essentially half to three-quarters of an inch.

You don't need a measuring device, essentially the width of your thumbnail is all that push rod should come out of the brake chamber.

So that's a fairly simple one and most provinces in Canada, most of the U.S.

states, all allow you to use the pry bar method.

The other method is the applied stroke method.

And again, the same principles apply:

1) chock the wheels;

2) release the parking brakes;

3) make sure you got over 90 psi in the system.

Now for the applied stroke method you're going to need another person or you're going to need a board or something that will allow you to apply the service brakes in the applied position.

So after you pump up over 90 psi and whatnot, you go around make sure that you mark all the push rods at a fixed point.

Some of these will have plastic tabs on them as you'll see when we go out to the truck here.

You'll see that this unit that we're working on today has plastic tabs on it that rest against the face of the brake chamber.

Most of the time the face of the brake chamber is going to be your fixed point for determining if your brakes are in adjustment.

So you go around, mark all of the pushrods, if they're not already marked or there aren't plastic tabs on them as are there are on this unit.

You go back into the truck and apply the service brakes in the fixed position, so they're held on.

And then you go around the unit and you measure every one of the push rods for how much travel there is when it comes out of the brake chamber.

Now on a type 30, which is the most common on the back of trucks and buses and semi-trailers, is going to allow two inches of travel - maximum 2 inches of travel.

So if you're already at the 2-inch limit, you're going to need to get them in adjustment and the way that you get them an adjustment is with a six-pack.

So you're allowed a maximum of two inches on automatic slack adjusters.

If you have, in the rare case, a manual slack adjuster which you probably won't have in this day and age, you're allowed an inch and three-quarter - so maximum 2 inches of travel on a type 30.

Now the front steer axles, the brake chambers are going to have different-sized chambers.

If you're on a bus or a smaller vehicle that has air brakes on it you're going to have a different size brake chambers Now what determines your pushrod travel--how far that push rod can extend out of the brake chamber--is the size of the brake chamber - so the diameter.

So essentially, if you get pulled over by the DOT, the CVSE or some other diesel bear, what they're going to do is going to take their callipers and are going to measure the diameter of your brake chamber.

And then they're going to look up on their chart and they're going to determine what size the brake chamber is.

And from what size it is will determine how far the pushrod can extend out of the brake chamber.

So if you're going to a driving school and they're sending you to for license, they're going to tell you how far that can extend out of the brake chamber if it's an applied stroke method.

In most cases, it's not going to be an applied stroke method.

So you measure all of them, determine that there within adjustment.

If they're in adjustment you're good to go; if they're not in adjustment and their automatic slack adjusters you want to do what's called a six-pack to walk them back into adjustment.

Because there's a couple of reasons that automatic slack adjusters will go out of adjustment: first of all, they don't get enough grease; or second, there aren't hard enough brake applications to ratchet it over to the next notch inside of the mechanism.

Because essentially, that's all it is is a ratchet mechanism inside of the automatic slack adjuster.

So what you do is, keep your wheels chocked, go back and make sure your parking brakes are released.

6 Pack Adjustment

Pump the system up to maximum pressure and make three hard brake applications.

By the time you make three hard brake applications, you are going to be below 90 psi, so pump the system back up to maximum pressure again.

And again, make three more full hard brake applications.

That's called a six-pack! Once you do that, often times, you go back up to the automatic slack adjusters and you check them again - oftentimes those six hard brake applications are enough to walk your automatic slack adjusters back into adjustment.

So you just check again - if they're not an adjustment after you do a six-pack you basically take the unit to a mechanic and they'll swap out the automatic slack adjuster, because at this point that's what's wrong.

It just simply needs to be replaced.

Sometimes you can put grease to them, because if they dry out oftentimes the ratchet mechanism won't work.

So you can put grease to them and try another six-pack and sometimes that might walk the automatic slack adjuster back into adjustment.

For the most part, the slack adjuster simply needs to be replaced and you're going to have to go and find a mechanic to do that for you.

So today we're going to go to the truck here we're going to show you both the pry bar method--sometimes called the free stroke method--and the applied stroke method on the truck.

Now we're going to get underneath the semi-trailer because it's easier to video that for you and give you a better image of how that is done.

It's actually--once you see it, it's actually--quite simple to determine adjustment of air brake systems and determine the brakes are in fact in adjustment.

So let's head out to the truck.