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Rear Suspension Air Bag Question


747Flyer
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I have a 1998 Volvo 610. It is the first and only HDT I have owned. Is there some type of valve that is supposed to prevent the suspension air bags from deflating when the truck's air system leaks down over time? I have been putting a jack stand under the rear frame when I plan to park the truck for a few days, as I simply don't like the way it looks sitting there when it squats after the air system has leaked down. Assuming there is not a leak in the bags themselves, should they remain inflated (check valve??) even when the air system has leaked to zero? My truck has a Trailer Saver hitch installed and the gauge for it indicates that it retains air pressure even when the truck's air system has leaked down - this is what set me to wondering if the suspension air bags should do the same.

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The leveling valve is between the air source and bags and will only exhaust air when the deck height rises above the set point as would happen when the load is removed. Otherwise, in my perfect world, rear suspension air pressure should the same “forever” if the load doesn’t change.  Possible leak sources are the leveling valve, air lines and fitting and the bags. Our truck suspension will hold for 3 or 4 days or so and the air bags and leveling valve are relatively new. 

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Only speaking of the air suspension on my Spartan mountain master MH chassis. Like Case said leveling valve, or dump valve switch, height control valve are the most likely places.

ref: https://www.volvotrucks.us/-/media/vtna/files/shared/body-builder/manuals/volvo_section-6-suspension-and-steering.pdf/   page 45 and up.

Don't shoot me for trying to help.

Edited by Ray,IN
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3 minutes ago, Jim & Wilma said:

The leveling valve is between the air source and bags and will only exhaust air when the deck height rises above the set point as would happen when the load is removed. Otherwise, in my perfect world, rear suspension air pressure should the same “forever” if the load doesn’t change.  Possible leak sources are the leveling valve, air lines and fitting and the bags. Our truck suspension will hold for 3 or 4 days or so and the air bags and leveling valve are relatively new. 

I'm confused ( happens a lot, LOL) by your response. You stated that the bags should hold basically forever, but then say that your suspension will hold for 3 or 4 days. Is the latter fairly normal? That's about what mine does. If parked longer without being started, it squats. Should I throw money at it, or again is this about normal for these trucks? Thanks.

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10 minutes ago, Ray,IN said:

Only speaking of the air suspension on my Spartan mountain master MH chassis. Like Case said leveling valve, or dump valve switch, height control valve are the most likely places.

ref: https://www.volvotrucks.us/-/media/vtna/files/shared/body-builder/manuals/volvo_section-6-suspension-and-steering.pdf/   page 45 and up.

Don't shoot me for trying to help.

I appreciate your post!

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9 minutes ago, 747Flyer said:

Should I throw money at it, or again is this about normal for these trucks? Thanks.

There are folks whose truck suspension will leak down overnight and those that, well, stay up for many days. For ours, I’m fine with several days and see no harm in losing the suspension other than it takes a bit longer I suppose to get underway waiting to air up the tanks.

Agree with others the leveling valve is a good place to check.  If leaking, it’s pretty easy to replace and not a bad preventative maintenance task in any case.

 

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1 minute ago, Jim & Wilma said:

There are folks whose truck suspension will leak down overnight and those that, well, stay up for many days. For ours, I’m fine with several days and see no harm in losing the suspension other than it takes a bit longer I suppose to get underway waiting to air up the tanks.

Agree with others the leveling valve is a good place to check.  If leaking, it’s pretty easy to replace and not a bad preventative maintenance task in any case.

 

👍👍

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The older trucks have air leaks. It's a given, you can chase them with the "Whisper" thingy, I think SuiteSuccess had one at the ECR the year I attended and many people tried to find their leaks. 

I've owned my truck for over 10 years I think and from day one it wouldn't keep air in the bags. Recently it's gotten better, but I have no idea why. 

Letting the truck run long enough to build up air pressure is the time you should be doing your pre trip evaluation. Mine is usually done before I'm ready to put it in gear. If yours is taking too long it might be more important to check out the compressor. 

Insomnia is why I'm here at this hour. It may have affected my response, but I don't think so. 

 

Rod

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9 hours ago, 747Flyer said:

I have a 1998 Volvo 610. It is the first and only HDT I have owned. Is there some type of valve that is supposed to prevent the suspension air bags from deflating when the truck's air system leaks down over time? I have been putting a jack stand under the rear frame when I plan to park the truck for a few days, as I simply don't like the way it looks sitting there when it squats after the air system has leaked down. Assuming there is not a leak in the bags themselves, should they remain inflated (check valve??) even when the air system has leaked to zero? My truck has a Trailer Saver hitch installed and the gauge for it indicates that it retains air pressure even when the truck's air system has leaked down - this is what set me to wondering if the suspension air bags should do the same.

747Flyer, with a truck up there in "truck years" chasing air leaks can turn into a full time "hobby". I would venture an opinion that your 21 year old truck is equal to 80 human years, an age when controlling flatulence becomes a problem. In more technical terms air lines become very hard and brittle after just few years in service, as do the O-rings and gaskets in the air fitting. My truck was 5 years old when I bought it and 15 years old when I got rid of it. If I got 3 day before it squatted all the way down, I was happy. Lot's of airlines and fittings to chase.

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1 hour ago, phoenix2013 said:

747Flyer, with a truck up there in "truck years" chasing air leaks can turn into a full time "hobby". I would venture an opinion that your 21 year old truck is equal to 80 human years, an age when controlling flatulence becomes a problem. In more technical terms air lines become very hard and brittle after just few years in service, as do the O-rings and gaskets in the air fitting. My truck was 5 years old when I bought it and 15 years old when I got rid of it. If I got 3 day before it squatted all the way down, I was happy. Lot's of airlines and fittings to chase.

A gassy horse will never tire

A gassy man is a man to hire🤣

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Be aware that the levelling valve can have internal and external leaks. External leaks are the kinds that leak bubbles or the "Whisper" can detect, and are just like they sound. Air pressure leaks to the atmosphere. Internal leaks are trickier. The truck pressure can drop, through separate leaks, while the suspension levelling valve will try to donate air to the system, to keep it pressurized. This is not how they are intended to work, but it does happen with wear. This is often too slow of a leak for even a "Whisper" to detect.

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Here's another reason why this can turn into "fools errand" on senior citizen trucks. As I mentioned above the air lines stiffen with age, the reason, the material (plastic) from which they are made is hygroscopic, meaning, it absorbs water from the air. It's that absorption that turns it from nice and pliable to stiff and brittle. Combined with quick connect (push in and seal) air fittings this is great for building trucks air systems quickly and efficiently. It also works well for years. So why do old trucks develop flatulence? New trucks; soft and pliable line plus engine and road vibration, no problem, Old trucks; stiff and brittle lines plus engine and road vibration, flatulence. You can get away (sometimes) replacing the air fitting where the leak is, with old lines using a new quick connect fitting might not solve the problem, using a "real" DOT brass fitting is a better choice, you can crank them hard enough to stop the leak even on old stiff lines.

Edited by phoenix2013
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 You may want to look on youtube for a Infineon air leak detector. Years ago it was on the forum about them and several of us on the forum purchased one. I have one and in two weeks or so I will be using it on our truck as it is leaking down in a day now.

   Hopefully someone on the forum may have a picture of one. Ours is in hiding at this moment or I would post a picture of it.

  I could not find it in the resource guide.  With a quick search.

 

   Vern

Edited by Wrknrvr
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Thanks for the correction Darryl.

 

my mind was on my own project today.

  I does work rather good. It may need a better head phone set. But I have found some small air leaks that would have been all but impossible to find without it.

 

   Vern

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I am outfitting my 730 with a hose quick connect to air up things but I also made an adapter to allow the male quick connect to allow me to use my small compressor so that I can fill the air system without having the truck running.  I also use kids bubbles as my leak detector of choice.

 

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8 hours ago, Lance A Lott said:

I would be ecstatic if mine stayed up 1 hour, and I mean the entire system not the rear bags, I have to let the truck air up if I stop for lunch. 

Took me several weekends to fix the one hour air down.

Find a leak fix it

Find a leak fix it 

Find a leak fix it

And so on........

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On 11/23/2021 at 10:14 AM, Wrknrvr said:

 

 You may want to look on youtube for a Infineon air leak detector. Years ago it was on the forum about them and several of us on the forum purchased one. I have one and in two weeks or so I will be using it on our truck as it is leaking down in a day now.

   Hopefully someone on the forum may have a picture of one. Ours is in hiding at this moment or I would post a picture of it.

  I could not find it in the resource guide.  With a quick search.

 

   Vern

I have one. Thanks.

 

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Hello My 1984 Peterbilt 359 suspension is usually good for "2" Months even in cold weather. The other air is good for "1" week. It has way more places for leaks-even has air wipers than newer trucks. They used rubber lines with flare fittings. Bought some new seats and they go down in a week were the old Peterbilts never did. They got plastic lines with push-loc fittings

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One item to be aware of, at least on our Freightliner, that as the suspension drops, the truck will move slightly. Be careful that it does not fall off or tilt the jack stands when it does. Ours will lose some air overnight to the point the suspension drops, but it varies based on air temperature. The warmer it is the slower it runs low on air. 

Typically, if I am not going to unhook for an overnight stop, I manually drop the rear suspension using the dash switch (I have to do it a couple times as my switch automatically defaults to the up location and so it airs back up the suspension when you take your figure off of it. This way I don't have to hear it bang when it lets the air out itself in the middle of the night. 

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When the air leaks got so bad as to drop the suspension during a 1 hour stop for dinner while traveling, I decided to fix it.

I aired up the truck st the Schrader port on the governor, I grabbed a large bottle of kids bubble mix. I poured it in a spray bottle started at the rear most air bags, and sprayed every air line connection.

I worked forward fixing or replacing any component that made bubbles.

The Truck will stay up for weeks, and has not "folded" the big bags in the rear even after sitting over a month.

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