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.
PASS CDL Air Brakes First Time - take this comprehensive course!
A course for truck, bus & RV drivers operating a vehicle fitted with air brakes.
This self-paced course gives you:
• more than 100 practice test questions with feedback; • EASY step-by-step instructions how to conduct a pre-trip inspection on an air brake system; • DETAILED rules to use air brakes and brake downhill with a large vehicle safely; • step-by-step instructions and precise wording for pre-trip inspection of trailers with airbrakes; • explained SIMPLY to you is the tractor protection system and its components.
Illustrations, checklists, & cheat sheets ensure your success
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.And I'll explain that a little bit later.
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.
At the Truck
Hi there smart drivers, welcome back.
Rick with Smart Drive Test talking to you today about checking pushrod travel adjustment for air brakes and determining that your air brakes are in fact in adjustment.
Pry Bar Method (Free Stroke Method)
So the first test that we're going to do is the pry bar method or the free stroke method as it's sometimes called.
This one is actually quite simple and all you need for this test in terms of tools--they do state in the California State airbrake manual, the CDL manual--that you can do this with your hand, but you can't do this with your hand.
You can't pull that push rod out of this brake chamber with just your hand.
So what I suggest, gloves.
Always get gloves to protect your hands - safety.
You need a prybar – a catspaw works well.
You can have all kinds of different pry bars.
They have them at truck stops and those types of places.
You can pick them up.
They work really well, and in some jurisdictions you might need a tape measure.
But as I tell students, it's just the width of your thumbnail - half to three-quarters of an inch in the province of British Columbia, Canada.
I know in the state of New York and California, and in other jurisdictions they allow an inch.
But for the purposes of what we're going do today, we're going to use the width of our thumbnail.
And like I said, you can get a tape measure and when you pry it out just measure with this.
But it is approximately the width up your thumbnail.
So you can see here - just put the pry bar on the clevis pin at the end of the push rod and pry out on it.
And you should be able to determine that it is within adjustment - half to three-quarters.
This is not the most reliable test, but for the most part it works well.
And most jurisdictions allow the pry bar test (free stroke method).
Next test we're going to show you is the applied stroke method and this one is a little bit more involved.
And in the province of Ontario, Canada for those students doing their test in Ontario, Canada you'll have to have the tools to be able to do this test.
Applied Stroke Method
The applied stroke method: 1) wheel chocks, as you can see here in the image, so you can secure the vehicle and release the spring brakes on the unit.
And then you're going to have to do an applied stroke method.
As well with the applied stroke method, if you get pulled over by the diesel bears: the CVSE, the MTO or the DOT in the United States, the applied stroke method is the method that they're going to use.
Now as I said, it's two inches of pushrod travel on a Type 30 brake chamber.
On different brake chambers, for example, on the front theses are smaller brake chambers.
It is the size--the diameter of the brake chamber--that determines pushrod travel.
So what the diesel bear is going to do is he or she is going to measure the diameter of the brake chamber and they're going to look on his/her chart.
And you can find--I'll put a link down in the description box there for the diameters of the brake chambers to determine maximum pushrod travel allowed.And so if you're doing the applied struck method on the front, you're going have to determine that if you go to a driving school.
They're already going to know what size of brake chambers you have on the front of your vehicle and how much pushrod travel you're allowed, but for the most part authorities are going to do applied stroke method.
On a Type 30 brake chamber and with an automatic slack adjuster you're allowed two inches of pushrod travel.
If you've got manuals, which is very unlikely in this day and age, you're allowed one and three-quarter inch of pushrod travel on and applied stroke method.
So let's get to the applied stroke method and show you how to do that.
So the applied stroke method - when you get in the cab you'll need to chock the wheels as you can see here in the image and you need more than 90 pounds per square inch of air pressure in the air tanks after you release the parking brakes.
If you don't have over 90 psi, the spring brakes are not off completely.
And you can't check the pushrod travel on the applied stroke method.
So the other thing you're going to need to do after you release the parking brakes and have over 90 psi - you're going need another person to hold the service brakes on or you're going to need something to hold them on, like a stick that you can jam in between the brake pedal and the seat.
And for those of you going for a road test and doing the applied stroke method, you're going to need a stick or some other method to apply the service brakes while you're out underneath the vehicle measuring the pushrod travel after you've applied the service brakes.
And that's how you're going to have to do that.
So you can see here on the push rod that there's a marker--a yellow plastic marker--on the push rod here.
And this is going to be our fixed point.
If you don't have yellow markers you can also mark that with soapstone or you can use a zippy tie.
And you can put a zippy tie on there, as well, for your fixed position.
Now what we're going to do is we're going to in the cab and we're going to apply the service brakes.
Alright, so we've got the service brakes applied.
We know that the face of the brake chamber is our fixed point and we're going to measure out to the yellow tab on here.
Because we know before we apply the service brakes--released the parking brakes and applied the service brakes--that the yellow tab was sitting right flush up against the face of the brake chamber.
So what we're going to do is we're going to measure that distance.
And you can see that it's just less than 2 inches on that one and on this one we can see that that one is just under 2 inches as well.
So both of the trailer brakes are in adjustment.
Now these are close to the adjustment limit of two inches, so basically what we would do is do a six-pack on this, which is essentially go in the cab, pump up to full pressure and make three hard full service brake applications.
Build the pressure back up.
And again, release the parking brakes and make three full-service brake applications.
Often times, that will walk the ratchet mechanism inside of the automatic slack adjuster back into adjustment - cause it to ratchet over to the next spot on the ratchet and bring them back into adjustment.
So that's something you might want to do because these are very close to the adjustment limit.
But they are within limits and you wouldn't be put out of service if you got pulled into a scale by the CVSE, the DOT, or the MTO in Ontario.
Conclusion
Quick review on checking adjustment for air brakes.
You have either the pry bar method--the free stroke method--or you have the applied stroke method.
For the applied stroke method you're going to need something to hold on the service brakes - a stick or another person.
Oftentimes, it's better if you have another person to hold on the brakes for you, but that's unreliable.
So find something that you can use to hold the service brakes applied.
If you're at a school and you're going to go for driving test and you need to hold the brakes on for the purpose of your road test, obviously the school is going to have to have something you can jam in there.
So a stick, and you're going to need a measuring device.
You're going to need some way to mark the pushrod - a lot of these trucks will just have the plastic tabs on them as this one does, as you saw there.
And then what you do is release the parking brakes, make sure that you got over 90 pounds of pressure to make sure that the spring brakes are completely off.
Apply the service brakes, go back and measure from your fixed point, which in this case was the face of the brake chamber, and in most cases it's going to be the face of the brake chamber out to that plastic tab.
And on a Type 30 brake chamber with automatic slack adjusters, you are going to need less than 2 inches of travel.
If you have a manual slack adjuster, which in this day and age is going to be unlikely, you're allowed an inch and three quarters.
That's the applied stroke method.
And the other one is the pry bar method or the free stroke method.
And you're going to need gloves--use gloves for both of these because always protect your hands and keep the dirt outside of the vehicle.
And you're going to need a pry bar.
And just put this in the clevis pin at the end of the pushrod - half to three-quarters of an inch.
In the state of California or New York, you're allowed an inch.
Most of the time you can just check the push rod travel against the width of your thumbnail.
The pushrod should not extend more than the thumb width out of the brake chamber.
Essentially what you're doing is checking the free play - the clearance between the brake shoes and the drum.
When you pull out on that you're allowed half to three-quarters or an inch in the state of California for that.
And in the state of California, they say you can pry the pushrod out with your hand, but you cannot do it with your hand, and you're going to need a pry bar to pull that push rod out of the brake chamber.
So that's how you do brake adjustment.
Question for my smart drivers:
Do you check the adjustment on your brakes every day or do you do it just when you have hill checks and you're driving through mountain?
Leave a comment down in the comment section there, all that helps us out.
I'm Rick with Smart Drive Test, thanks very much for watching.
If you like what you see here share, subscribe, leave a comment in the comment section.
As well, hit that thumbs up button.
Check out all the videos here on the channel - lots of great information for those of you getting a license or working towards a career as a bus or truck driver.
Good luck in your license.
And remember, pick the best answer not necessarily the right answer.
Must be used whenever two sources of air are used to operate a single device or system. For CDL air brake test, the driver must know there are 2 in the system.
OBSOLETE Independently applies and releases the trailer service brakes. Knowledge Test Question: This air brake control is not to be used for parking. Although most tractors are still equipped with hand valves, beyond a trailer service tug test, these air…
Applies the parking brakes of the air brake equipped vehicle indefinitely – if needed of course. The parking brakes are held in the “ON” position by the mechanical force of the springs; these spring parking brakes are held in the “OFF” position by system air…
OBSOLETE Used on some vehicles with dual air systems. This device provides a means of using the force of the spring brakes to assist in stopping a vehicle in an event of a failure in the rear (primary) air system.
Slack adjusters have three purposes: 1) To convert the forward linear motion of the push rod into rotary motion of the camshaft. The slack adjuster works on exactly the same principle as a box end wrench on a nut. 2) To act as a lever, thus generating greater…
Stores compressed air for braking and for other air operated accessories. The air tanks are the first fail-safe in the air brake system. In the unlikely event that the air compressor fell of the side of the engine, the air tanks (reservoirs) store enough air…
OBSOLETE Fills the trailer air tanks (reservoir) and applies and releases the trailer service brakes. The relay emergency valve also applies the trailer emergency brakes in the event of a trailer breakaway or normal disconnect. Knowledge Test Question: In the…
OBSOLETE To reduce application pressure to the steering axle by 50 % compared to the drive axle brakes, when required by reduced road conditions (rain, snow or ice). The system consists of a dash switch with 2 positions: Dry Road: 100% front wheel braking; in…
MUST KNOW The brake pedal applies the service brakes - truck, or truck and trailer brakes. In other words, the brake pedal brings the vehicle to a stop when it it depressed. SHOULD KNOW The foot valve operates the secondary and primary sub systems…
To stop the vehicle, brake linings rub against the brake drum. This action creates friction, converting the vehicle's forward energy of motion into heat energy, which stops the vehicle’s tires. If the tires have traction, the vehicle will come to a stop. The…
To reduce application pressure to the steering axle brakes during most braking situations. Reduced pressure to the steer axle brakes occurs for most braking applications. Only during hard braking is there equivalent pressure delivered to both the front and…
The gauges are in either pounds per square inch (psi) or Kilopascals (kPa). These measure the amount of air pressure in the primary and secondary air tanks.
A cattle chute with one-way gates allows the cows to only move in one direction – forward. A one-way check valve in an air brake system works exactly the same – it allows air to only move in one direction – forward through the system. The one-way check valves…
Using the pry bar method, confirm that the brake is in fact out of adjustment. After confirming that the brake is out-of-adjustment and it is equipped with a manual slack adjuster, complete the following steps to bring the brake back into adjustment. If one…
Depending on which province you're in, the air buildup time or compressor test has somewhat different paramenters. Still, all require that the diesel motor be at a fast idle. A fast idle on a diesel engine is between 900 &1200 rpm.
The National Safety Code madates that every driver of a commercial vehicle equipped with air brakes must check push rod travel every day. In many jurisdications, drivers are allowed to use the pry bar method; in others , they must use the applied stroke…
The National Safety Code madates that every driver of a commercial vehicle equipped with air brakes must check push rod travel every day as part of his/her pre-trip inspection. In some jurisdications, drivers must use the applied stroke method; in others, they…
The other method is the applied stroke method.
But as I tell students, it's just the width of your thumbnail - half to three-quarters of an inch in the province of British Columbia, Canada.
So both of the trailer brakes are in adjustment.
