Air Ride to Spring Conversion

[Saxis]

The original plan for my Denali was to adjust/extend the Air Ride sensors to gain lift in the rear, along with Liftmeister in the front. I did a bunch of searching on the OS about all kinds of OEM Air Ride problems, lowering, etc. One option I have is just replacing the OEM system with Z71 Tahoe springs. I have a few questions about doing this:

1: With Z71 Tahoe springs, would I then be able to use the Liftmeister rear kit as well, or even a complete BDS kit?

2: With Z71 Tahoe springs, would it be possible to install Air Lift 1000 bags like Roadie's, and hook them up to the OEM compressor?

Question #2 has me intrigued. The possibility of gaining lift while still retaining the benefit of automatic Load Leveling.


I'll still probably just adjust my sensors to start, see how it rides for a while. I know the OEM bags can give it a good 4-5 inches of lift empty. I had it loaded to the roof with firewood once, and after turning the truck off and unloading, the rear was jacked way up.

[The Roadie]

I haven't posted my suspension pics in my build thread yet, but the components are there now. Go look at it.

Yes, you can do Z71 springs PLUS the BDS or Mark's spacer.

I actually see no systems reason you can't replace the OEM air bags with plumbing to fit the Airlift bags. Except for the unreliability of the OEM compressor, that's a cool idea. If I was doing it, I'd make sure to put in some miniature valves to disable the OEM compressor when it dies on the trail, and be able to inflate the Airlift bags through a Schrader valve, which comes with their kit. Excellent idea.

[Saxis]

I was thinking/hoping the Air Lift bags would be/are a bit more durable and reliable than the OEMs, maybe less prone to leaking with some new plumbing. Hopefully, that would put less stress on the OEM compressor and prolong its life also. Pretty much just an upgrade of the entire OEM Air Suspension. How do your Air Lift bags hold up? Have to check/refill them very often, on the trail and off?

Another concern with this would be the ride. I'd pretty much use the Z71 springs for lift. Since I don't haul much for gear, except while camping, long trips and towing a small boat, it might be a little rough when empty.

[The Roadie]

They hold up fine and never leak. I fill and dump them from controls in the console.

   TrailVoy Thread  

You need 5 PSI minimum to retain their warranty, so that might possibly be an issue with the OEM compressor. You'll have to instrument it to be sure. They also can't be allowed to go over 35 PSI IIRC.

[Saxis]

Hmm... you don't think the OEM system keeps at least 5 PSI in the bags at stock height? I find that hard to believe considering how low some vehicles get when a component fails, but maybe it doesn't. I haven't been under there to look at mine yet, but how hard would it be to put a gauge on the OEM system and see where it sits? I do know the OEM compressor really struggles to put more than about 35 PSI into a tire...

[The Roadie]

Sorry, I meant to imply that the stock compressor's algorithms probably can't handle running as low as 5 PSI, so you might not get the ride height down. Yeah, since the air bag system doesn't have springs to carry most of the load, they probably never go below 20 PSI normally. Different shape for the pressure/deflection chart.

[Trail X]

You think the stock air ride system monitors pressure? I don't have a wiring diagram in front of me... but I'd imagine its a fairly simple system. You have a fill and a dump trigger, with their signals filtered so not to fill or dump every time you hit a bump.

So as long as you adjust the trigger mechanism so it reads 'level' when the vehicle is unloaded, and the bags have about 5-10 psi in them... I don't forsee an issue...

But then again... if the system monitors the bag psi to help estimate the load... ick.

[Saxis]

I don't see why it would monitor pressure other than as a "safety", like the WirelessAIR system from Air Lift, which monitors for pressure drops below the safe 5 PSI. Probably doesn't even have that though. That's what the sensors are for. It must have some kind of filter to keep it from adjusting all the time though. Maybe a polling interval to check for consistency in the sensors? That would make sense to me at least...

[Trail X]

Or a simple low-pass filter.





A 3-pos switch could create a square wave of sorts... seems it could be filtered by a standard filter... but then again, this is all speculation until I can look at the wiring diagram in the service manual.

[The Roadie]

It's a digital controller, with built-in firmware. Pretty extensive algorithms for dumping pressure after a certain time, detecting leaks, blinking the LED for error codes (no serial data link to the BCM), and deciding if the compressor is trying to raise the vehicle and not succeeding. All digital filtering and smoothing algorithms.

[Trail X]

Of course it couldn't be simple.

So is that an affirmative that it does measure pressure?

[The Roadie]

It certainly measures pressure, and uses two RVDTs for measuring the angle of the height sensor arms, but I don't know what the allowable ranges are.

http://en.wikipedia.org/wiki/RVDT

If I had this on the Roadiemobile, I'd just rip the control electronics out, manually control the fill and dump valves, and add an analog gauge where I could see it for the system pressure. As has been noted, the compressor isn't geared for offroad size tire inflation.

[Trail X]

RVDTs eh?... this is where the MEs need to just shut up.

EEs Rule (this thread at least )!

[Saxis]

So it would all boil down to whether or not the pressure in the Air Lift 1000 bags would fall into the "safe" zone of the OEM system. It'd be handy to know that range. Quite a few of the SS guys adjust the sensors to lower as much as 3-4". You'd think that would be quite a pressure drop, but I can't recall reading any reports of problems associated with that. Probably just a cut-out to prevent under/over inflation? Actually, under-finflation is probably an under-statement. Wouldn't the weight of the vehicle alone give a baseline pressure reading? The only way you could really drop below that pressure would be an open (leaking) system? I'm certainly no ME or EE though...

I guess the "automatic" part of the OEM system is really what appeals to me. If I become dead set on going this route, it'd be worth a shot. It can always be ripped out for manual pressure/height monitoring.

[Saxis]

So my Z71 Springs should be on my doorstep when I get home from work. I've still been contemplating ordering a set of Air Lift 1000 bags and giving the stock compressor a shot, until I came to my senses: That compressor is just complete crap and needs to be disabled and removed. Still... the on-board air is a nice feature, whether the damn thing over heats or not in a couple minutes of use. Once again I began my search for a suitable replacement compressor. Looking at Air Lift's compressors, I came across their Leveling Fill Station. Doesn't look half bad! Comes with Compressor, 2G Tank, Gauge and Control, Aux Air Line, Hoses/Fittings. About $350 and $80 for the bags. The problem I have, is making it look as close to stock as possible. I ran across a thread of an Admin at TBSSOwners group who did something similar, using his stock air bags with an Air Lift compressor, but no on-board air. He also used the wireless control to inflate/deflate on the fly though.

Here is what I'm thinking:
Remove the stock Air Ride down to the sensors, bags, compressor and controls. Mount the Air Lift compressor and tank in their location. Probably do some cutting to mount the new gauge/control in the rear panel where the stock controls were, hook up the Aux line to my stock Aux connection. Then I just have to run new lines to the new bags (since they're 1/4" instead of the stock 5/32", no dealing with adapters), then cut/splice into the stock compressor power.

It would be manual control of the air bags, which would probably be fine for me. I don't haul much gear continuously. Just the occasional tow or camping trip. I can't imagine I use the compressor a bunch, and it probably wouldn't be enough to run air tools, but much better than airing tires or whatever else. At least much better than the stock compressor, which allows you to put 10 pounds into a tire in about 20 minutes after letting it cool between 1 minute shots of air.

I'm hoping there's enough room to mount the compressor and tank. I haven't really crawled under there to scope it out yet...

[Trail X]

Do you have the XL? You'll have more room under there if you do.

A 2 gallon tank is still pretty big, but not terrible... and can generally be tucked away... just a matter of crawling around under the truck a bit and scoping it out.

[Saxis]

Nope, not an XL. Just a SWB Denali. I'm kinda wondering about the resonator area. I haven't removed my resonator yet, but that's in the future plans also. Seems like the tank would be quite a bit smaller than the resonator, would be in close proximity to the compressor and control panel, but might have to be careful on keeping the lines away from the exhaust. Shouldn't be too hard. The SS guy left his stock compressor in place and mounted the new one above the spare tire. He just spliced into the power and actually kept the stock compressor in working condition for the auxiliary air. Kind of a waste, IMO, unless his compressor doesn't overheat like usual. He just adjusted his sensors to the lowest position so the stock compressor never kicks on automatically. I wouldn't have problem, as everything would be replaced.

[Saxis]

Crawled under there a bit last night. Not very much room with the spare tire in place. If I took that out after I get new tires, there'd be plenty of room. Might be able to squeeze the tank up under the rear bumper. Right behind the driver's rear tire there's a bunch of space also, but that would be a lot of hose to run back to the passenger side, and it would get caked with mud/grime. I'll probably run with just the springs for a while and see how that goes. Not extremely excited about spending another $430 quite yet without knowing how it'll work.

[Saxis]

Done!

Converted to Z71 Springs and installed the BDS lift + 1/2" shim this weekend. Picture of the lift is updated on my Build Thread

Didn't have the time to tear apart the AirRide and remove the compressor with all the lines. Weren't sure how the lines were connected to the springs either, so we just cut the lines about 6" above them. They deflated and we pulled them out. When I get the AirLift 100 bags and new compressor + on-board air, I can hopefully remove all that crap and re-route everything in the stock locations. The compressor should be easier to get to when I cut off the resonator, also.

Also, BDS says to re-install the rubber isolator when doing the rear lift. The stock air springs don't have a rubber isolator, and I installed the Z71 Springs directly onto the axle perches. I thought it may make some noise or something, but I drove around a good 60 miles already and it rides great! Seems like a bit of vibration in the front between 40 and 55mph. I need to get it aligned though.

[KE7WOX]

Done!

Converted to Z71 Springs and installed the BDS lift + 1/2" shim this weekend. Picture of the lift is updated on my Build Thread

Didn't have the time to tear apart the AirRide and remove the compressor with all the lines. Weren't sure how the lines were connected to the springs either, so we just cut the lines about 6" above them. They deflated and we pulled them out. When I get the AirLift 100 bags and new compressor + on-board air, I can hopefully remove all that crap and re-route everything in the stock locations. The compressor should be easier to get to when I cut off the resonator, also.

Also, BDS says to re-install the rubber isolator when doing the rear lift. The stock air springs don't have a rubber isolator, and I installed the Z71 Springs directly onto the axle perches. I thought it may make some noise or something, but I drove around a good 60 miles already and it rides great! Seems like a bit of vibration in the front between 40 and 55mph. I need to get it aligned though.

I don't see the updated thread.

I noticed that vibration too, around 50 MPH (IIRC it was gone when I hit higher speeds on the freeway), so that is probably due to the alignment. I have put that on hold since I hope to get new tires this week.