Envoy / TBSS rear air suspension problem

[eclipse5302]

I've got an issue with my air suspension. I've got the right-side sag going on, I believe both due to a weak front spring and malfunctioning rear bag, but it only seems to get really bad when the truck is shut off.

The compressor does run a bit (once every few minutes or so) when the truck is running and the truck stays mostly level. It seems like when I turn the truck off, the truck instantly sags on the right side within seconds - almost like the solenoid is intentionally opened after key-off. I've already checked the lines and the bags for leaks, and found nothing.

Any suggestions?

[stuart]

Wish I had an answer, also wish someone else would have posted one for you. Mine started out intermittent. I started parking farther a bit off the driveway to allow my wife better clearance when backing out of the garage in her car. The back drops off the slab into the grass and I figured the sagging happened because the GMC's rear was lower and torquing something causing a leak. The problem didn't seem to occur on flat pavement. Now it has progressed to constant sagging while parked. It doesn't sit down immediately but rather after being parked a while.

Bought a Chiltons but it only addresses remove and install of the air spring. I hate to bring this to the dealer and get ripped off if I can do it myself.

Thanks,

Stuart

[n0kfb]

How carefully have you checked the air bags for leaks? The system need to be checked at full extension and also full compression of the air springs, because leaks can be hidden by the spring 'cones' or seats.

DO NOT get under your vehicle without supporting it with jackstands! If you should somehow disturb an air fitting and vent an air spring, you could be crushed!

Having said all of this, I'm going to guess that your trucks have worn-out compressor assemblies.

Let us know what you find!

-- Dan Meyer

[stuart]

Thanks Dan. Can you clarify a couple of things?

When you say full extension I assume you mean when the air spring is fully inflated and the vehicle is in normal position. As for compression are you referring to when all the air has leaked out?

If the compressor assembly is worn out it can still inflate the spring to normal or close to normal level? It seems to hold during around town driving. I assume that even though I don't hear the compressor often during driving it is topping off the air bag as it loses pressure.

I'm not sure this is an item I have the time to go through a learning curve with, if I take it to the dealer am I in for a large repair bill?

Thanks again,

Stuart

[n0kfb]

I don't know why I didn't notice your request until today. Sorry about the delay.

Full extension would be with the truck body high and the wheels drooping as far as they will go. This needs to be done because part of the air bags are hidden against their seats, and the leaks might be hidden. The problem with this is the system will reduce the air pressure in the system because it sees the body as high, and the lower air pressure will tend to reduce any leaks.

From your problem description, I'd guess there is a valve that is not sealing in your compressor package. Unfortunately GM only sells these junk compressors as a unit. They get a ton of money for what amounts to a cheap imported compressor, a couple air solenoids and a cheap electronics package.

Send me a e-mail at n0kfb@n0kfb.org and I'll reply with what little documentation I have about the air suspension.

All standard disclaimers apply.

-- Dan Meyer