Learn how to correctly adjust automatic slack adjusters on an air brake system.

How To Correctly Adjust Air Brakes On A Semi Truck https://youtu.be/0txYDO_uu5Q

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Introduction

– 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 ten, there’s something wrong with the automatic slack adjuster.

And it needs to be replaced. Learn how to adjust brakes on a semi-truck using the 6-pack method.

Don’t…Don’t Take on the Liability

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. 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. Unless you’re a qualified technician, never put a wrench to the adjusting nut on an automatic slack adjuster. So if you put a bit of grease to them and then do a six pack. That’s what I’m going to show you how to do today. A six-pack 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 fix your problem. If not, you need to take it into a technician. So let’s show you how to do this. When working around and under the truck, always chock the wheels with a proper wheel chock.

Safety First – Chock the Wheels

First thing you need to do, chock the wheels. Make sure that the wheel chocks are are placed under the tires, because you’re going to release the parking brakes.

And you don’t want the vehicle to roll away and crash into a tree, and 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. 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. Ensure the air pressure is at maximum before doing the 6-pack technique to adjust the automatic slack adjusters on the air brake system.

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 released the brakes. We’re going to pump to maximum pressure, and we know it’s at 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. 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. As part of your daily pre-trip inspection you are required to check push-rod travel to determine air brake adjustment. 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.

How to Conduct the 6-Pack to Adjust Automatic Slack Adjusters

The air dryer has purged. We see that the needles have stopped climbing, therefore, 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. For maximum braking capability and efficiency, all brakes must be adjusted correctly. So we made three brake applications. We pump it up again because we’re now below a hundred pounds. And as I said, we want to get maximum push rod stroke so that we ratchet over to the next notch in the cog. So we bring it back up to maximum pressure again. Maximum pressure, air dryer is purged, needles have stopped climbing. Three more hard brake applications. After doing a 6-pack to adjust the brakes, be sure to re-check to ensure that brakes are in adjustment. 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. You go back out, recheck your push rod travel, and eight times out of ten 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 the defective automatic slack adjuster. 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.