My wife’s GMC Envoy has been dragging its rear pretty much every morning for the last couple of weeks. It usually happens when it’s warm in the daytime and the temperature drops overnight. There’s a slow leak in one (or both) of the air bags in the rear. I’ve determined this because the suspension always comes back up when you start the car and rides normally after the bags re-inflate. The air bags just need to be replaced before they no longer re-inflate and we have to drive it down the road with the back end all the way on the ground.
The first step in the procedure is to get the rear of the truck up in the air and all of the weight off of the rear suspension. There’s a little kink in the frame rail that looked like as good a place as any to put the jack stands. I removed both rear wheels using the trucks lug wrench (located under the driver’s side rear passenger seat) as well as the spare tire for easy access.
The next step is to unbolt the air compressor bracket that is located behind the passenger side rear wheel, up above the muffler. These two bolts are 13mm and were quite easy for me to remove. I assume it will be easy for everyone, but you never know. Once unbolted, you will need to push up and back to unhook the bracket from the frame rail. This took a little bit of jiggling but it came out fairly quickly. Once it is unhooked, you will just lift it up and turn it sideways so that it hangs off the side. Be conscious of the air lines that are connected to it, you don’t want to damage them.
Next, you will use a 10mm open ended wrench to loosen the two air lines that are connected to the front of the compressor. This will allow the air in the springs to be let out and make the removal of the air bags possible. You could loosen both at the same time, but I recommend doing one at a time so that you lessen the chance of getting dirt in the lines. In my truck, the clear line was the passenger side, and the black line was the driver’s side.
Once the air bags have been deflated, you will be able to remove them. To do this, you will need to reach over the top of the spring perch to depress the plastic lock that is on top of the airbags that holds it in place. Once it is depressed, you will be able to turn the spring and drop it out. Be careful not to just pull the whole bag down because the air line will still be connected to the top of the bag and it is not long enough to bring it down to a level where it is easy to work on.
You will need to disconnect the air line from the old air bag. To do this, you will have to press down on the steel ring that is sealing the air line in place. Don’t use any tools here because you do not want to damage the line. It takes a little bit of grunt to hold the air bag, push down on the steel ring, and pull the line out but it can be done. Just be patient and you will get it done, take a little time here so you don’t have to replace any additional parts later.
I purchased the Arnott Air Bags directly from Arnott, but if you use the link to the Amazon site they are cheaper. The installation is the exact reverse as the removal. The only difficult part is the re-insertion of the air line into the top of the bag. The Arnott bag makes it really easy, just pull out the shipping pin and push the air line in as far as it will go. I was able to get them to go in pretty much to the bubble that is in the line. There was a little space between the top of the seal and the bubble but it was miniscule.
I also decided to replace the shocks while I was at it. I purchased the KYB Excel G shocks for the rear of the truck from Rock Auto. These were super easy to replace. There are two bolts that connect the shock to the vehicle. Both are 18mm, the top one bolts to the frame rail and the nut is welded to the frame so it comes right out. The bottom one bolts to the axle and requires you to hold the nut on the other side to remove the bolt. I used the closed end of a wrench because I did not have a deep socket 18mm, but that would work as well. This was as simple as taking the old one out and putting the new one in, 5 minutes per side tops!
The Air Bags don’t reach all the way down to the bottom perch when you first install them. They are in the shipping configuration so are not inflated at all. Something to be aware of when you are lowering the truck back down to the ground, obviously you would put the tires back on but as it comes down you will want to make sure that the bottom perches line up correctly with the Air Bags. When I did it there was not problem and they seated properly, but I did look to make sure that would happen.
Don’t be alarmed when you put the truck back down on the ground, when I did it was lower than I have ever seen it! It was so low in fact that I could not get the jack out when I lowered the final side on the ground. I needed to use my lowered vehicle jack to jack it up enough to remove my monster jack. Just turn the truck on and let the air bags inflate. They will pump up and level the truck if everything was installed properly.