- You've done your pre trip inspection on your vehicle.
You've determined that one of your push rods
is stroking too far.
In other words, it's out of adjustment
and you need to figure out how to adjust that.
In this day and age, all new trucks, all new vehicles
with air brake systems are going to be fitted
with automatic slack adjusters.
And you may have erroneously been told that,
in fact, you can adjust an automatic slack adjuster,
and you can, but nine times out of 10,
there's something wrong with the automatic slack adjuster.
And it needs to be replaced.
As well, in terms of liability,
God forbid that something happens, you get in a crash,
and the authorities find out that you were under there
adjusting automatic slack adjusters,
that could end very badly for you.
So in terms of liability,
I recommend, highly, highly recommend
that you do not do anything
with automatic slack adjusters.
One thing you can do,
most of the time
what happens with automatic slack adjusters
is they don't get greased.
Because they don't get greased
the ratcheting mechanism inside stops working.
So if you put a bit of grease to them
and then do a six pack,
what I'm going to show you how to do today,
is essentially pump the air brake system up
to maximum pressure, three hard brake applications,
pump it back up again, and to do three more.
Most of the time, that's going to rectify your problem.
If not, you need to take it into a technician.
So let's show you how to do this.
First thing you need to do, chock the wheels,
make sure that the wheel chocks are in the vehicle safe,
because you're going to release the parking brakes
and you don't want the vehicle to roll away
and crash into a tree, explode into a fire inferno.
So be safe, wheel chocks in,
and then we'll pump the system up maximum pressure,
three hard brake applications,
and then do it again.
And then we'll recheck push rod travel
to see whether that fixed our problem for us.
If not, you need to get it to a technician
and you need to have them replace
the automatic slack adjuster.
So the first thing you do is start up the truck here.
Parking brake is on, obviously,
pumping the system up to maximum pressure.
We want to release the parking brakes on the vehicle.
So for example, we don't have a trailer on the truck here.
We got wheel chocks in, so we've release the brakes.
We're going to pump to maximum pressure
when we hear the air dryer purge,
and then we see that the needles have stopped climbing.
We can throttle up here a little bit.
(upbeat music)
The reason you need maximum air pressure in the system
is because you need to make a hard service brake application
to try and get the ratchet mechanism
to ratchet over to the next pawl.
Think of a boat ratchet,
that you're ratcheting up the boat onto the trailer.
That's exactly the same thing that's happening
inside an automatic slack adjuster.
(upbeat music)
Air dryer is purged, needles have stopped climbing,
we're at maximum pressure.
Now we make, we have our parking brake released,
three hard maximum brake application.
We can see that with the brake application.
Two,
and then three.
So we made three brake applications.
We pump it up again 'cause we're now below a hundred pounds.
And as I said, we want to get maximum push rod stroke
so that we ratchet that over to the next one.
So we bring it back up to maximum pressure again.
(upbeat music)
Maximum pressure, air dryer is purged,
needles have stopped climbing.
Three more.
Hard brake applications, shut the truck off.
And we go out and we recheck
and make sure that the push rod stroke
is now within tolerance.
After you do your six hard brake applications in the cab,
come back out, recheck your push rod travel,
and eight times out of 10
it's going to go back into adjustment.
If not, you'll need to take it to a technician
and they'll either need to be adjusted by them
or they'll replace it.
Don't be doing it yourself.
Don't take on that liability
in the unlikely event that something happens.
You just don't want to do that
for the complete playlist on air brakes
and pre-trip inspection determining push rod stroke
that you're within adjustment
both the applied stroke method and the pry bar,
click over here and remember,
pick the best answer.
Not necessarily the right answer.
Have a great day.
Bye, now.
If you want the complete list,
detailed list of what you need to say,
what you need to inspect
for the purposes of passing your pre-trip inspection,
Click up in the corner here,
head over the Smart Drive Test website.