Rear air suspension slow leak

[310-1983]

Hello! My 1983 310 motor home rear air suspension has a slow leak that I am not having any success in locating. It will leak down from 80 psi to 30 psi in a period of about 8 hours.

It HAD a major leak from one of the airbags. I replaced the airbags, and the tired Thomas electric compressor has been replaced with a modern Firestone unit. I have inflated the system to 80 psi and sprayed all fittings, the airbags, the pressure switch, and tank seams with soapy water, daubed them with a small sponge dipped in soapy water. I have taken an automotive stethoscope and removed the rod and diaphragm, using the hose to listen for air leaks.

Has anyone had any similar experiences with the rear air suspension? How long is normal for it to keep the vehicle lifted?

The "Pumptrol" pressure sensor switch looks original, wondering about it, although it passes the soapy water test.

Any thoughts?

[rmkrum]

There might be an internal leak somewhere that is not causing visible bubbles. Consider isolating sections with the use of a connector that has an air valve and a gauge that you can pressurize from another source to isolate the part that is leaking...

I would start with the air bags and associated piping. Disconnect and install your test fixture, manually pressurize to 80 psi, and watch the gauge. if it holds pressure, reconnect. and move backward toward the next component.

From your description, I would wonder if the control valve is having an internal issue. Try blocking off it's output to the air bags, put the test gauge on that output, and see if it holds pressure.

Another possibility is that it may be normal (designed into the system somewhere) leakage that the air compressor can easily keep up with?

Disclaimer: I don't own one of these motorhomes (yet). This is from an engineering perspective from a semi-expert wrench swinger on many automotive systems...Dilbert is a friend of mine, and I have the 'Knack".

https://youtu.be/Dx6HojLBsnw

[Waipio Rim]

I believe that these came with a check valve downstream from the compressor to keep air from bleeding out through the compressor. Mine did not have a check valve when I got it and the air bags would leak down overnight. I got tired of being woken up at night as the suspension settled, and bought a check valve from Andy at Inland RV. It helped, but I am still chasing leaks.

[mayco]

Sounds like a missing or faulty check valve to me. Air will leak back through the compressor if your check valve isn't doing what it should. Proper operating psi in the rear system should be 85-110. Kick on at 85 and off at 110. My system will hold above 85 for 2-3 days, or there about.

[choctawmel]

I had the same problem with the 'Silver Bullet'. Just thought it did that. Then on a regular bases I would bicycle by this 1985 345 sitting in the yard and it was always up.
I think the compressor is the check valve. I finely found a cracked compression nut that screwed onto the compressor it self. Replaced and it never has gone down again.
I did just have to replace the compressor with the one the PO had rebuilt soon after he purchaser the unit new.
Which reminds me I need to contact the company and see if they still have the rebuild kit.

[WayneG]

If you do isolate it as not being a compressor problem, (Check your drain valve first)
I replaced my leveling valve and most of my leaks went away. (My compressor runs about once every 48 hours)

Besides the rear air bags, mine came equipped with air horns, I added lines and valves to my front air bags and I have an air hose fitting so I can top off the tires if needed.

I think my leveling valve would leak out of its exhaust port under certain conditions, mostly cold weather.

If you do any work under the rear end, be sure to put blocks in the air suspension so the it does not fall on you.

[Smartstream]

The above suggestions are all excellent. Did you receive a new check valve with your new compressor? Many compressor manufacturers will void the warranty if a new check valve is not installed.

You mention the system is loosing pressure, are you measuring the bag pressure, or the tank pressure? I assume by your description the ride height is going down. I so I would look very closely at the leveling valve. It can leak externally through the fittings and shaft seal but it can also leak internally through the exhaust port.

Lastly keep in mind that as slight leak is normal and acceptable. Systems that hold air for long periods of time are not unusual but not necessarily the norm. I have a couple of friends with the high end 40' plus coaches with automatic air leveling systems and their compressors cycle every few hours to keep them level. If parked next to them you can hear the pumps cycle in the quiet of the night.

[davejay]

Hey,
I would definetly consider the leveling valves first, check on compresser second, fitting third, did you use the original compression fitting? They don t Like to be reseated. And it is a possibility, that one of your new bags has a leak. Our Volvo trucks will hold air in the system for weeks. My 85 325. With original bags will hold air for months. So no it is not normal for them to bleed off. My guess is leveling valves. They do a lot of moving when your going down the road. If my memory serves me, I think they got little o rings internally. They get hard and flattened out. Any truck parts store will have the valve they re pretty universal. Take one of yours for a match up. And really, you only need one . I don t know why they didn t mount it right in the middle of the tag, or the middle of differantial. Mounting it on the tag was just a way to keep the bags adjusted ,so the tag was planted on the road, but in the center of it travel. Kind of a weird idea, I see the rational of it, but I'd still put it right dead center on drive axle.




On another note related, could someone tell me exactly where the wires go for the compresser? I replaced the floor in the rear and had to re drill the hole in the floor. My 25 mind said I'd remember where everything goes, but my 58 year old mind told it to shut up, we don t need to mark anything. So I got no running when I turn the key. It worked perfectly before I messed with it. So, I know everything did what is supposed to do. Patiance I a vulture I lack. I can jump it and it will work, but as soon as I remove lead it will stop. Help me, Said the fly

[WayneG]

Originally Posted by davejay

On another note related, could someone tell me exactly where the wires go for the compresser? I replaced the floor in the rear and had to re drill the hole in the floor. My 25 mind said I'd remember where everything goes, but my 58 year old mind told it to shut up, we don t need to mark anything. So I got no running when I turn the key. It worked perfectly before I messed with it. So, I know everything did what is supposed to do. Patiance I a vulture I lack. I can jump it and it will work, but as soon as I remove lead it will stop. Help me, Said the fly

On my 84 270 the compressor was wired to the accessory terminal on the fuse block in the dash. I replaced my old compressor and the new one drew more current and blew fuses occasionally, so I relocated my compressor DC supply to the house fuse block using a 25 amp circuit breaker to avoid replacing fuses. I also moved my compressor in under the rear bunk to keep it out of the cold, added a unloader and water separator. I re-purposed the outside compartment for storage.

[choctawmel]

I did some calling. All the number on the repair kit paperwork(from the 80's)and the pump didn't work, so, fired up my computer. Gast Manufacturing, Bar Harbor, MA didn't answer so I left a massage. Then I called Southwest Controls in Dallas. They still have rebuild kits for $100. I ask what a new one cost $649. I order a kit K-750. He did say they had a service guy and for $85 tier down fee they could do it. Lets see: $85+40(shipping two ways)+$100(kit)+ $??? build up labor
Then this morning I answer a call from Bar Harbor MA. It was Gast them self. He had a different kit #. I ask if K-750 would work, "Yes, that's better."
The pump does not have a check valve, Without a check valve it will leak.
Manual:https://www.scribd.com/document/1619...ss-Vacuum-Pump

When I swapped pumps, I don't remember what, how, who, where. It's a real bi#ch to get my 66 old body into the far right corner between the bed and the cabinets. Don't know why I didn't take pictures.

I did run a new #10 wire from front to back for both the compressor and fuel pump. The little wire they used had multi crimp splices.
I think the chassis came with the two pumps and when they extended the frame AS just splice a piece in for all the electric and fuel lines. Never trust a un-solder crimp.

[mayco]

Several folks here on the forum, including myself, have upgraded their rear compressor and switching/power controls. You can save yourself a great deal of hassle, add a port for an air hose for filling tires n such, and stop using the under sized wiring that Airstream installed to power the compressor. It costs a little up front but in the long run can save yourself a good deal of troubles in the future especially while on the road in the middle of nowhere.

In my case I chose to go with the ViAir 400c compressor.
https://www.amazon.com/Viair-40040-4...rds=viair+400c

I used their relay/pressure switch combo 85/105 for controls.
https://www.amazon.com/dp/B000FQ1HM4..._t1_B000FQ793A

#8 stranded copper wire direct to battery for power

30amp inline fuse or breaker on the #8 wire to battery

Reuse the existing ignition wire, already there for your relay switch.

Its simple to install, wiring is very straight forward, safer than the undersized existing wiring, and gives you enough compressor to install a quick coupler for an air hose. Comes in very very handy for topping off tires and maintaining proper psi in your front airbags.

So, for around $200 you can have a very nice system and get rid of the antiquated pressure switch, and the rest of the original wiring and controls. The ViAir compressor comes with an inline check valve that is replaceable by itself if it ever fails.
https://www.amazon.com/Viair-92831-N...FTS1CD477WSXSV


There are many compressors and relays to choose from and the prices vary according to power and output. But on the whole it's a worthy project to get your rear suspension up to par without breaking the bank. Very doable for those of average mechanical/electrical skill sets.

FWIW,

MIKE

[310-1983]

Originally Posted by 310-1983

Hello! My 1983 310 motor home rear air suspension has a slow leak that I am not having any success in locating. It will leak down from 80 psi to 30 psi in a period of about 8 hours.

It HAD a major leak from one of the airbags. I replaced the airbags, and the tired Thomas electric compressor has been replaced with a modern Firestone unit. I have inflated the system to 80 psi and sprayed all fittings, the airbags, the pressure switch, and tank seams with soapy water, daubed them with a small sponge dipped in soapy water. I have taken an automotive stethoscope and removed the rod and diaphragm, using the hose to listen for air leaks.

Has anyone had any similar experiences with the rear air suspension? How long is normal for it to keep the vehicle lifted?

The "Pumptrol" pressure sensor switch looks original, wondering about it, although it passes the soapy water test.

Any thoughts?

Hello! Updating on the leak down, I forgot to mention I bypassed the leveling valve early on in the process, will put it back as soon as I can get the system to hold 80 psi for at least 12 hours, then recheck. The new Firestone pump I installed has a check valve, don't know how good it is. Took the air tank out and discovered it has a leaky check valve on the inlet on the left side of the tank. Have one on order from Grainger. Fingers crossed!

[Voltair]

Originally Posted by davejay

Hey,
Take one of yours for a match up. And really, you only need one . I don t know why they didn t mount it right in the middle of the tag, or the middle of differantial. Mounting it on the tag was just a way to keep the bags adjusted ,so the tag was planted on the road, but in the center of it travel. Kind of a weird idea, I see the rational of it, but I'd still put it right dead center on drive axle.

The reason there are two leveling valves one each side off the Tag axle is maybe both being fed from the holding tank through their separate small 1/4 hoses up to their separate air bags.To keep up with the leveling valve's responses eg. exhaust and compression the bags will fill and deplete twice as fast with two leveling valves or if one is activated and not the other then it is a minor air adjustment . Lessening the time the tag axle is being over or underloaded .Nothing like a bent tag!
Regarding spiriles 12v electrical stuff. I have run 2 battery neg cables #1 from start battery directly to a bell housing bolt, easy got to through top front wheel arch, this fixted starter click clicks plus gauge issues. #2 ran same heavy neg battery cable from start ballery to rear tag area chassis, fixing my compressor running hot brighter tail lights..The original neg web strap to the chassis I cleaned but was In my opinion asking for an electrical ghost problem.
Regarding these observation: based only on how my 345 was setup, whether it was mucked with by PO duno....
Rus

[Isuzusweet]

Mine will keep its knickers up for roughly 3 months.

As Mayco Mike stated a numer of us have redone our systems from top to bottom. I went with a twin cylinder ARB continuous duty compressor (which I put in place of my old converter). I cut a couple of holes into the fridge gable to allow the heat to get out through the fridge vent. I also fabed up two 5 gallon aluminum holding tanks and a hose reel in the back with air regulator.

I hate leaks!

[davejay]

Hi all,
I'm going to rewire the compresser right to the power junction block on the frame. And put an inline fuse by the compresser. My problem is, when I disconnected all the wires to fix the floor , I forgot where the wires to the soliniod went. He had this thing wired with a switch to turn on/ off the compresser. Don t know why, but I wired it back to stock. Where do the orange and yellow wires go to.heavy white and red go to ground and power on compresser. I replaced the soliniod because I wanted to. Ther was a yellow wire that came off of soliniod and went to the gray box pressure switch. Where does that wire go to. There's three blocks on that relay. Maybe I put it on the wrong terminal. I think the yellow goes to the ign side, of the soliniod looking at soliniod , it would be the left term in front the big term on left is for power to compresser. Can you see why I need a picture? I'm getting lost talking about it. Any help would be most appreciated.

[davejay]

A comment on the leveling valves.
Those valves don t respond instantly, it takes a couple of seconds for them to start blowing off or letting air in. I think they put dual valves on the units because of road crown. . But what doesn't t make sense is this , the tag is a solid unit. If say your riding high on the right side and the left side is being loaded up due to ruts or a high crown, by letting aide out of the left bag, doesn't help to keep the right side tag tire on the ground. It just takes the load off the tag completely. You see my point? I believe the tag was put on the 325 s and up was for stability and a little more gross weight capability. Dumping air on the tag kind of defeats that purpose. You see my point? But I don t know how you could have made the tag independent suspension. It would be cool to put a steerable axle as the tag. Like the dump trucks . To much re engineering to make it worth while I think.. Not enough room for suspension components either. A front axle off of a p30. Workhouse chassis would fit . Disc brakes too. Same calipers as the MH too. Oh well, just a crazy thought.

[Voltair]

Hi Dave, That Henschen/Tag axle affair back there is hard to get our heads around at first because its a very Dynamic hookup. Sorta well thought out though, them designers were no fakes back then, so I slowed down looked and then took my hat off to them..
Now both bags are air linked together in that small top gap your having trouble putting your hands into, you'll see that a 1/4 hose link with a T in the middle, that ultimately finds its way back to the low pressure switch next to the compressor.
If you see where that control valve is situated on the chassis and its adjustable rod is attached to the Tag axle drop arm that the wheel/ brake assembly connects too, then one tag wheel can go up and independently from the other, the air control valve then operates either exhausts or pressure to both air bags because off that 1/4 air link. One side can not go up without the other:
If you were to put your foot under the tag wheel and get someone to drive forward over your foot let say a 5 sec trip you'll notice two things or actually three,for the first 2 seconds you'll not hear any air sounds, then you will with the 325 body raising up by pushing down on the drive wheels.This takes the extra load weight limit off those Tag Duratorque axles, good job it works that way as the end result otherwise as you'll notice as on some tag axles, the wheels are splayed out at the bottom, bent tag axle, got too much load for too longer time too many times. Simple job to straighten them on a press but dont bother just get your air bags working well.
Tricky to describe..Gosh..
Rus

[WayneG]

This is a diagram from a older manual

[bkahler]

Originally Posted by Isuzusweet

Mine will keep its knickers up for roughly 3 months.

Yeah, but you're using Canadian air, it's different than that what we have here in the states....

As Mayco Mike stated a numer of us have redone our systems from top to bottom. I went with a twin cylinder ARB continuous duty compressor (which I put in place of my old converter). I cut a couple of holes into the fridge gable to allow the heat to get out through the fridge vent. I also fabed up two 5 gallon aluminum holding tanks and a hose reel in the back with air regulator.

I hate leaks!

Nice setup!

Brad

[WayneG]

Maybe getting a bit off topic, but for a lightweight air hose, this is what I use and from the cabin door I can reach all tires on the 270.
I think it is 25' long. I store it in a 2 liter soda bottle in the center door below the right rear bunk.
For my compressor, I have it under my right rear bunk in otherwise wasted space between the generator and rear tire well.