Technical Airbag leak and uneven pressure

Hi all, on my 1950 ford shoebox I bought it with several issues I’ve been fixing little by little.

It has airbags on the front and rear, an Accuair VU4 manifold, and manual toggle switches along with a gauge for the tank, dual gauge for the front and dual gauge for the rear.

I have a few issues I can’t resolve:
1. When I fill the tank and then fill the front both sides inflate to about the same pressure about 140 psi or so at full. For the rear one side inflates about 20 psi more than the other. Oddly enough the side that I think has lower psi is higher by half an inch but I may need to carefully verify it’s that side that sits higher. Am I likely seeing this issue because I have one toggle switch for both sides of the rear? Since it has the vu-4 manifold I would have thought both sides would equalize during filling…

2. At fully filled the front goes up quite a lot and the rear goes up a fair bit but sits a good amount lower than the front.. is that likely due to the limited travel from the type of airbags selected for the rear or maybe a very deep c-notch?

3. I’ve found a bunch of leaks at the gauges and the manifold and coming off the tank which I fixed except for one. Somewhere the side in the rear with a lower psi reading has a leak.. about 10 psi drop in an hour. I sprayed with soapy water at connections going underneath and around the airbag but couldn’t find a leak. I can’t quite see the fitting going right into the airbag too well because of the floor/cnotch but maybe it’s there! I hear a faint tick tock noise like a clock and it sounds near the airbag but hard to confirm…. I used a hose and couldn’t hear exactly where it was coming from. There is a small leak for that side/rear off the manifold but it looks very tiny when I sprayed it. I’m going to fix it at the manifold and reevaluate how much psi I lose per hour but I suspect the leak is also elsewhere most likely at the airbag connection where I can’t see. Is that a common place for leaks?

4. Is it good for me to keep the car at 0 psi… fully deflated when parked in my garage for long periods?

 

I found the source of my leak in the rear. It looks like the connection at the airbag. I'm assuming this would be a royal nightmare to fix without taking the airbag out and it looks like there is a notch where the airbag sits so I can take it out with the fitting on there. Does anyone else see the same thing? I wonder if I can disconnect at the quick disconnect joint (where plastic line feeds in) once the line is de-pressurized and take the brass components and airbag out together and work on it outside the car. Is taking the airbag out a hard task? I have the car on jackstands on the rear. That was a pain in of itself along with taking out the small rectangular covers at the top of the c-notch to locate the leak!

Here are some photos:












Also, at the same time I have some small leaks in the Accuair VU4 manifold in the poppet connection (or whatever those things are called). I tried taking the plastic lines out cutting them a 1/4 inch or so and putting them back in but I still have some small leaks so I may need to buy a rebuild kit. If the airbag fitting/connection fix is a pain part of me says to just put this all back together and deal with it later. I tend to keep the bags deflated when parked and don't plan on being anywhere for long duration where I would need to be at ride height, nor would I be going far any time soon (or probably ever)... I'm getting antsy to drive this car find a woman to date and stop burning so much time in my garage by myself. I drove this thing once to the DMV in late March since I got it and that was it and I've been working on so many other odds and ends from things that were put together incorrectly. I didn't expect to encounter so many headaches... that's what I get for having too high expectations for what I paid and not seeing it in person before buying it....

I still can't understand with just two switches (one for the two front, one for the two back) why the non-leaking side inflates 20 psi higher than the leaking side. The leak does seem small but I would think it would equalize when I keep holding the fill switch open even after there is no more air flowing from the manifold to both bags. I would have thought the pressures would read the same even just for a short while until the side that leaks drops in pressure. For the front there is one switch and they both read pretty close to each other when filled all the way.

 

That valve block has four separate valves in it.

They are not connected to each other on the bag side.

If you have a single switch for the front or rear, that switch logic controls two valves.

 

Leaving it parked at zero psi is probably not a good thing. I say probably as it depends on how it's been put together. If the weight of the car is supported by the deflated bag the longevity ov the bag will be compromised. If proper bump stops, or lack of suspension travel, or the frame hitting the ground, or something else occurs before thx bags are fully squished then all is good.

You could put suitable wooden blocks under the frame before leaving paked up for extended periods.

Chris

 

Go back to Boyle's law. All things equal, and assuming you're comfortably between maximum compression and maximum extention, the only factor determining the pressure in a bag is the load on it. The leak at one of the rear bags is preventing it from holding the same pressure as the other rear bag, but that isn't all that is happening. The other bag is also carrying more of the weight of the rear of the car as a result of this. Of course it is going to show a higher pressure.

 

In other words, pressure can equalize only while both the valves controlled by the switch are open.

 

Great point! This is happening with the rear on frames though so no weight from the car causing a load. It would just be the load from gravity on the axle itself and shocks? I was expecting under this situation if I hold the switch for the rear open fully for a long time (like 30 seconds) for some air to travel from the non leaking side to the leaking side and equalize since the manifold valves would be open. I understand the manifold has 4 different fill valves but if both for the rear are open and held open for a while I would think air from the tank could flow such to equalize both. Perhaps I don't understand the internals of the manifold well enough or the leak is big enough to keep that from happening due to some load (even with the car on jack stands on the frame).

 

That's a great idea. I know the previous owner stored it at 0 psi when parked and I thought perhaps that's bad as it would cause the car weight to crush the bags. The car bottoms out maybe 1 inch from the ground so I can't even look down there. I may just put some blocks of wood under the frame for reassurance and leave it like that when parked in my garage. It's possible there are bump stops to keep the bags from getting squished fully but I would need a lift that I can drive on and look from the middle to see how its sitting.

 

Yea I noticed that manifold has four different valves and a single switch is controlling two valves. I thought if I hold the rear switch open and the two valves in the manifold are open the air could flow through the tank and equalize pressure on both sides... assuming I'm holding the switch open for a long time for it to do that after both sides are filled. I tried this with the car on jackstands so the airbags are not supporting the car weight and it still didn't equalize. It could be the small leak is not allowing it to do that as Ned pointed out.

 

Does anyone know if its a difficult task to get the airbag out with the fittings attached to it if I disconnect from where the plastic line comes in as shown in one of the photos above? Would it be just a matter of depressurizing the air in the line, disconnecting the plastic line and then removing the nut/bolt at top and bottom and sliding out or is there a lot of prying and using a jack to get things to move out easily?

I'm wondering if I should just take care of this while I have the chance if its not too difficult.

 

Without the weight of the car acting on the bags they will inflate to their maximum extention before showing any pressure above atmospheric. This is (hopefully!) a completely different condition from the way the car would be when in use.

Are the gauges sound? Have you tried swapping them around?

 

Thanks that makes sense they inflate to their maximum extension before showing pressure. I verified that yesterday by just barely hitting the switch to fill and looking underneath and seeing them fully extended while the gauges read very little if not near zero.

I haven't tried swapping the gauges around. It could be an issue with the gauges for sure where one is reading more than the other. There was a leak at the gauge that I fixed though.

One thing I did notice is when it was on the ground, one side sits higher by about half an inch and I can't remember if the side leaking sits higher or lower... I remember it being the opposite of what I expected when I measured but I hadn't found the side with the leak yet at that point so maybe I was thinking the other side was leaking.

 

An airbag setup is almost always a custom, one-of-a-kind installation. There's no way anyone can predict how much effort it can take to remove or replace a particular component because that will vary from case to case depending on what the original builder did.
Your airbag system is older and has a lot of time and miles on the clock. And as you're finding out, it has a good amount of deferred maintenance issues. The questions that you are asking are going to be best answered by yourself or whoever else is going to tackle each issue one at a time. If a particular airline has a leak, it's probably time to replace and/or upgrade it end to end, from fitting to fitting. The hard part of the system is done. changing out all the airlines with new, fresh lines and fittings is small potatoes. I'm not saying every fitting will be easy to get at. You just have to do whatever it takes to get at 'em.
The gauges are also "older" and may or may not be reading consistent with each other. But that may be a moot point anyway because adjusting each corner of the vehicle to the same air pressure is the wrong way. Adjusting the height (stance) of each corner of the vehicle will tell you how much and how different the pressure each needs.
You may want to re-engineer that back axle so you can adjust each side separately so it's not sharing a single switch.

 

Can you find 4 coil springs the right size?

 

Thanks! That all makes sense, I guess I'm trying to ask the question how do I go about removing the airbag so I can work on the fittings? If I deflate and loosen the top and bottom nut/bolt and remove the plastic line at the quick disconnect point should that be all I need to do to get it out (I'm assuming I'll need to pry, etc). I'm hoping for some insight so I don't do something wrong in the process.

 

I see why some complain about the pain with the air suspension setup...

 

Deflated it should theoretically come out really easy as the deflated size is considerable smaller (at least shorter) than the extended size. Totally unlike a coil spring in that regard.

You need to have your wits about you though as unlike working on a regular car there's the added dimension of variable suspension. On the other hand that's commonplace on new stuff these days!

Chris

 

Thanks for the response! I'll give it a go and see if I can get it worked out of there.

 

Well, yes. That's the approach any of us would start with. You may find that you have to jack the body and frame up to let the axle hang down to its full extension to make enough clearance for the bag to come out. But there's always the chance that additional components will still be in the way and also have to be disassembled.
The best advice I can give you is to consider the project open-ended and don't count on it being done by sunset. Plan on the vehicle remaining in place for a while and have other transportation options for getting to work, etc.

 

Thanks so I have the rear on jackstands on the frame at the moment. I haven't driven this car since March and it was a quick trip to the DMV. I can't even close the driver side door after installing the new weatherstripping so I definitely don't expect to finish anything quick. I am about to order an Accuair VU-4 rebuild kit so I don't mind if I have the car on jackstands another week or two.

 

Quick question I found a leak on the airbag itself in the rear right where the rubber meets the top hard base. I measured 9 inch extension at 120 psi. Is there any trick to buying new airbags? I couldn’t make out a brand name in mine.

I've seen some on ebay for instance that have 9 inch extension and min height of 2.7 inches... while I've seen some pricier ones from Slam Specialties that have 11 inch extension and the same min height of 2.7 inches. I do notice with full air pressure the front of the vehicle is definitely quite higher. I can get a jack underneath the back at full pressure but its slightly tight.

Also saw some from a brand "Air Lift" with minimum height of 2.8 and 12.5 max height which is a lot more than what I have now. I wonder if my front bags are a different type that have larger range.

Also for brands are there any I should gravitate towards... Slam specialties?

 

If you are buying new bags look for bags that have an internal bump stop.

From the description of your bag leak, it sounds like it has been over extended. You may have to put limit straps on them to prevent over extension. Make sure your bags match side to side.

Air Lift and Firestone are likely the best known in air bags

 

Thanks for the advice. So it could have been overextended by me just fiddling with the system... but at the same time I feel the car could go a little higher than it did even with full air pressure ~ 120 psi and the 9 inch lift... I definitely plan to buy two bags for the rear. The internal bump stop is a good idea! I also thought maybe these went bad from the previous owner letting the car sit at 0 psi for storage.. at least that's what I gathered because with the leaks eventually it went down to 0 psi!

 

I'm narrowing down my search to Slam Specialties SS Series..

https://slamspecialties.com/W/slam-products/ss-series/

I currently have some unknown brand with 6 inch diameter and 9 inch max height when full and seems 2.7 to 2.9 inches when fully compressed. I can't tell if they have internal bump stops.

The ones I'm looking at from Slam Specialties have internal bump stop. I'm not sure if I should take this opportunity to go with SS-8 which has 8 inch diameter and extends up to 13 inches and compressed down to 2.7 inches. Anything I should be weary of if I go with ones that size? It does seem there is plenty of room for 8 inch diameter with my setup and I did feel the back doesn't go up all that high with the ones I'm replacing.

 

https://en.wikipedia.org/wiki/Air_suspension
fix all leaks first.
the change in height front to rear was designed and built by the person who sourced and installed the parts/system.
as mentioned, corner weights will affect the height when pressures are equal, but your issue seems to be mainly a leak.
air bags can have internal bump stops, but just like air shocks, common sense seems to indicate there should be some pressure at all times.
since you don't have all the specs for the setup, I would suggest inspecting the components for identification and to check the installation (welds, clearance, and overall workmanship). You can make changes and repairs once you know what you actually have.
I applaud you supplying pictures, they may help those with more experience help you with this. Having your location in your avatar helps those who might be able to point you to a professional in the area for further assistance with your current situation and for sourcing any new parts. Online places may be cheaper, but the in person eyes on the problem can't be done nearly as well.

 

Thanks all great advice I appreciate! I found out the airbags are Slam Specialties 6 inch diameter and they appear to be the SS6 but quite older. I found the leak with soap/water solution right where the airbag rubber meets the upper mounting disc. Since they have internal bump stop (confirmed these older ones have them according to Slam Specialties) I think they just wore out from age and hence the leak.

With the car on jackstands at the frame , the axle and shocks and 4 link setup, and airbag out/deflated I measured 8.5 inches from the top to bottom mounting surface where the air bags fit. After talking to Slam Specialties support the SS6 or even SS7 would work but SS8 may be too big and the ride may be too soft. I'm thinking to go with the SS6 to be consistent with what I already have any not introduce any new variables. The SS7 might give me more extension but I don't know if the limiting factor are the shocks as far as not being able to get any more than 9 inches with the previous SS6 at 120 psi which should go to 11 inches according to their specs. I didn't want to try my luck prying at the differential to see if it can go more than 9 inches although I do have a scissor jack.

The shocks and 4 link were put together fine from what I can tell and likely causing the 9 inches limit I had seen before.

Short term plan is to replace the two airbags.. fix the leaks (ordered a repair kit for the Accuair VU4 manifold), replace some of the plastic line and add two more switches so I can control each wheel separately.

Longer term plan is to buy the e-level kit from Accuair and wireless controller.

 

Or being overextended.

 

Right! So this may have happened when I was looking for leaks. I took the old airbag out and set it on the differential and connected the line and inflated to 120 psi so I could trace the leaks without thinking about the over-extending part. I may have prematurely damaged the airbag.. however they do appear old and I can barely make out the logo.

When installed in the car, I don't know if they can over-extend unless the car hits bumps and bounces? The longest distance I measured with the car on jackstands at the frame is 9 inches. I would think if the car was on the ground with the weight on the bags it wouldn't raise any higher than the 9 inches. The SS6 supposedly can extend to 11 inches. Next, with the car on jackstands at the frame, the max distance I measured with the bags deflated or removed is 8.5 inches so I don't think gravity is causing over-extension when on jackstands.

I imagine it was old age in combination with the stupid thing I did to inflate not in the mounted position when checking for leaks.

 

Just went to the SS website and looked under Tech for a FAQs or Do & Don'ts or other bag related help. They provide wiring and routing, installation etc. but no general warnings I saw quickly. You assume that you were a partial cause of the failure, but I would hope that the bags can handle a single unloaded full inflation. Do they provide max height by 'blowing up' one and throwing it away? What weight load is minimum acceptable at full inflation?

When you get the replacements, ask for them to 'school' you on this and any other things to avoid. Knowledge can be gained.

 

Thanks! In fact the last question I sent to the Slam Specialties rep earlier this afternoon was if I did something wrong inflating it at 120 psi uninstalled in the car to check for leaks... I'm curious if they rate them at 250 psi and you fill them to 120 psi if that would over-extend and damage them if there's no weight load on them.
I will circle back when I hear back on that question. When I get the new ones I'm not going to inflate them unless installed in position.