How to: Replace Air Suspension with Coils

mfnman88

Original poster
Member
Nov 12, 2016
30
Dundee
Time: 1-2 hours
Difficulty: Easy
Tools needed: Spring compressors, big Flathead/Smaller prybar, Wirecutters or needle nose pliers.

Air ride suspension was put on several years/models of the GMT family including:
2005-2009 9-7X (all trim levels)
?-? Trailblazer SS
?-? Envoy Denali
?-? Bravada
?-? Rainier
(If anyone knows exactly which Trailvoys came with air ride post it and I'll update here till its finished)

This offers a "nicer" ride and keeps the rear end up even when adding a lot of weight such as a trailer by adding or removing air from the airbags in real time with an on-board compressor. These compressors along with other parts of the system (especially airbags) eventually fail and can be costly to replace. (The compressor unit alone is between $400 US and $700 US depending on what site/brand you use) Simpler solution is to just take out the airbags, which are conveniently the same size/shape as the coil springs from other GMT's rear ends, and replace them with said coils. Here's how.

My 9-7x was bought with a bad system (wouldn't turn on) and 1 bag was hissing when I squeezed it. The other bag didn't so I assume it was leaking pretty bad and ran the pump till it cooked something. Long story short.. my ass was on the ground.
IMAG0734_zpsr6ybpzpf.jpg


So here's what I did:
1. Put the thing on the lift (jack stands are fine but lifts are SO much better)

2. Find the Bags. (hint: they look like big rubber bags sitting on top of your axle)
IMAG0736_zpstsggfcfh.jpg


3. Pry the bottom end of the airbag out of the cup. (I had to jab a flat head screwdriver between the plastic on the bottom of the bag and the spring perch to break it free then it was simply putting a prybar in there and wedging it backwards)
IMAG0737_zpsufscourx.jpg


4. Twist the entire Airbag counterclockwise as if you were unscrewing it. The top should rotate about an inch and come down a few inches. (Again, I had to give it a little "kinetic motivation" with the prybar. I pushed sideways on the top plastice till it popped and then the whole thing wiggled in place.) Once you get them unhooked they'll still be attached to the airline, so don't yank them out yet. Notice in the next two pictures that there are 3 tabs on the airbag that will get released from the 3 slots in the top spring perch when you rotate the airbag. Also note that the top perch has a round lip in the center. That's important later.
IMAG0741_zps558xvwm2.jpg

IMAG0743_zps8h55edyq.jpg


5. After the bags are free you should be able to wedge them sideways just enough to pull the airlines out of the bags with either needle nose plyers or wire cutters. (or just cut them since I assume you wont be using the system anyway) I left as much as I could up there so I could possibly use it later for an air spring assist somewhere down the road.
IMAG0740_zpsetrjwvwv.jpg


6. Get a pair of Coil Springs and the rubber seat that goes on top of the spring between the coil and the upper spring perch. Autozone.com calls it a Spring Isolator. It will not only fit over that round lip we talked about in step 4 to keep the coil more centered but will also cut down on any squeaking from the bare spring rotating against the perch as it gets compressed and released when you hit bumps. (I was cheap and needed to be on the road yesterday so I went to a local salvage yard and got a pair of springs with the isolator for $25.
IMAG0745_zpscfo73aky.jpg

Side note: Spring rates, strengths, and lengths vary from model, trim level, and even year. All will "fit" and hold your rear end off the ground but at different heights and ride qualities. I've read you can even put Coils out of a GMC Yukon Z71 to get a lift but someone will have to confirm that for me.

7. Compress the Coil spring, set the Spring Isolator in the top of it, and put it up where the airbag used to be. The coil will have a smaller and larger end. The side with the SMALLER of the 2 ends will go DOWN. The Isolator should only fit in the Larger Top side. I had better luck pushing the Drivers side coil up from the back side of the axle, and the passenger side up from the front side of the axle.
IMAG0747_zpsr7umwlp0.jpg


8. Release tension on the spring evenly making sure the top and bottom stay where they're supposed to until there's some tension then you should be free to fully release one side completely, then the other.
IMAG0749_zpslfpmoj93.jpg


9. Set her on the ground and measure how far off you were at guessing what spring would make your GMT360 sit level with the front. (I was off by 1 1/2" with a junkyard set but now I know what to switch to next when I have some time/money)
IMAG0750_zpswf8kch3w.jpg
 

AWD V8

Member
Jan 12, 2015
463
Good write up.

I didn't use a coil spring compressor. I slipped my floor jack under the rear axle, removed both lower shock bolts. This allowed the axle to drop down enough to place the coil springs. Jack up the axle, insert and tighten the shock bolts.

Just in case a coil spring compressor isn't available. A floor jack would likely be needed to lift the axle up.
 

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