Air Ride Suspension and Air Brakes--Explanation

[barmcd]

I'm a little fuzzy about how these systems work together. My coach has hydraulic levelers, instead of air, in case that makes a difference.

The coach doesn't sag when parked, but the air pressure gauge slowly bleeds off pressure. After 5-6 days, it's down to zero. When I start the coach, the brake air pressure alarm sounds until air pressure builds up to about 80 psi, then it goes off.

I'm assuming the air tank for the brake is empty when I start the coach, so how does the coach remain level? Is the air system for the suspension totally separate from the braking system? Or do they share some components?

[photopilot]

I looked on the Monaco web site for your owner's manual, but they start with 2001. The brochure there says you have a 3-point HYDRAULIC leveling system, which you confirm. The brakes and air suspension are connected and share the same reservoirs, and are pneumatic- they use air, whereas your leveling system uses a separate hydraulic pump and valves. I'm not sure exactly how the 2000 air system is plumbed vs. the 2001, but you might look in the 2001 manual to see an explanation of how the air system works. There's a pretty detailed explanation in my 2006 manual.

Good Luck!

[zmotorsports]

Originally Posted by barmcd

I'm a little fuzzy about how these systems work together. My coach has hydraulic levelers, instead of air, in case that makes a difference.

The coach doesn't sag when parked, but the air pressure gauge slowly bleeds off pressure. After 5-6 days, it's down to zero. When I start the coach, the brake air pressure alarm sounds until air pressure builds up to about 80 psi, then it goes off.

I'm assuming the air tank for the brake is empty when I start the coach, so how does the coach remain level? Is the air system for the suspension totally separate from the braking system? Or do they share some components?

Dennis, the air system starts at the compressor on the engine and feeds both the brake system and the air bag/suspension system. Obviously there are a lot of other components in there as well such as ping tanks, air dryer, etc. but for the basic system the air compressor builds pressure to supply the two above mentioned systems.

If you air pressure is bleeding off in 5-6 days you should be able to hear a leak and locate it by ear and then once you get close use a water/soap mixture and start spraying connections and air lines until it reveals itself.

The brake system needs pressure to release the park chambers and then it uses air pressure to apply the brakes based on treadle position. Once the system gets up to around 80-ish psi a shuttle valve will also allow air to enter the air bags and raise to ride height and stop based on the adjustment/placement of the ride height valves.

There are some basic DOT tests that should be performed and if you are unfamiliar with air brake systems I suggest you google them and get to know them, they are of benefit to the safety of you, your passengers and anyone else on the road to become familiar and use the quick basic air tests before traveling.

Things like getting the system to max pressure (cutout pressure) or actually anything over around 120 psi and set the park brake. Watch the gauge after the first initial pressure drop from the set, make sure it doesn't drop more than 2 psi in a single minute.

Next, start the coach and pump your brakes to get the pressure down to 85 psi and start the timer, it should build back up to at least 100 psi in 45-seconds. Those are at least the two tests I tell people to perform as they check the initial integrity of the system for a large leak and the it tests the compressor to ensure it can build pressure at the required rate.

There are other tests but those two I feel are the most important. I will check and see if I can locate the DOT reference and post it for you.

Mike.


On edit, I almost forgot, the hydraulic leveling system is really independent of the air brakes and suspension. The only way they are connected is that the air suspension will dump during the deploying of the leveling jacks on some coaches automatically, others manually have to be dumped.

[zmotorsports]

One more thing, you also want to check the low air alarm and make sure it comes on around the 60 psi range. Just pump the brakes and dump the air to get down to where the audible alarm comes on.

Mike.

[zmotorsports]

Found it. There is a much longer version but this is a quick procedure that I suggest you familiarize yourself with.
Pre-Trip Inspection | Brake Check | Commercial Driver's License

Mike.

[JohnBoyToo]

Subscribing

Ours will leak down after a couple of weeks,
but I don't have air leveling, just air brakes.

and I would love to be able to dump the air and level at the lower height, but ours requires the engine to be running to level, thus it pumps the bags back up while I'm trying to level :(

I do realize that the default for the brakes is ON with no air pressure and only when it gets to 50 psi or so will the alarm go off, then only about about 90 psi I can release the brake, then it normally runs about 120 psi ...

[zmotorsports]

Originally Posted by JohnBoyToo

Subscribing

Ours will leak down after a couple of weeks,
but I don't have air leveling, just air brakes.

and I would love to be able to dump the air and level at the lower height, but ours requires the engine to be running, thus it pumps the bags back up while I'm trying to level :(

I do realize that the default for the brakes is ON with no air pressure and only when it gets to 50 psi or so will the alarm go off, then only about about 90 psi I can release the brake, then it normally runs about 120 psi ...

Just for clarification or maybe to set your mind at ease, they ALL leak down over time. There is no such thing as a completely air tight, air system. A good tight system will bleed off starting at the ping tank also showing on the gauge after several days and will start to bleed off at the suspension in a week or so. If you start noticing the coach leaning or bleeding off at the suspension before much of a decrease in the ping tank then you more than likely have a leak at a suspension component connection, such as at an air bag connection. Air bags do leak on occasion and can rupture but it is much more common to find a connection or connector leaking than a bag. If the coach is leaning to one side in a short period of time, it merely means you have narrowed down the side the leak is on and halfway to finding it.

Much more than that and I recommend going around your system with a spray bottle of soapy water and trying to locate the leaks. But don't worry because your system bleeds down over a period of a couple of weeks.

Mike.

[twinboat]

Deleted

[96 Wideglide]

Originally Posted by barmcd

I'm assuming the air tank for the brake is empty when I start the coach, so how does the coach remain level? Is the air system for the suspension totally separate from the braking system? Or do they share some components?

Your air bag suspenssion system has check valves installed.
So even thou your loosing a little air in your tanks over time, your suspenssion system must be in good shape, since your coach is remaining level.

[mel s]

Originally Posted by photopilot

The brakes and air suspension are connected and share the same reservoirs, and are pneumatic- they use air, whereas your leveling system uses a separate hydraulic pump and valves.

barmcd
That's why your coach remains level, (doesn't sag) when parked.
Mel
'96 Safari

[96 Wideglide]

Ha, never thought about that Mel !!

I 'assumed', the OP was talking about his coach remaining level, without using the leveling jacks.

[barmcd]

Originally Posted by photopilot

I looked on the Monaco web site for your owner's manual, but they start with 2001. The brochure there says you have a 3-point HYDRAULIC leveling system, which you confirm. The brakes and air suspension are connected and share the same reservoirs, and are pneumatic- they use air, whereas your leveling system uses a separate hydraulic pump and valves. I'm not sure exactly how the 2000 air system is plumbed vs. the 2001, but you might look in the 2001 manual to see an explanation of how the air system works. There's a pretty detailed explanation in my 2006 manual.

Good Luck!

I've got the manual, both the printed and on-line version. Interestingly enough, they are very similar, but the on-line version has more technical details in some areas.

I've read all the areas that pertain to the air system--it's mostly geared toward maintenance of the systems. I guess I was looking for a little more information.

[barmcd]

Originally Posted by zmotorsports

Found it. There is a much longer version but this is a quick procedure that I suggest you familiarize yourself with.
Pre-Trip Inspection | Brake Check | Commercial Driver's License

Mike.

Mike,

Thanks for the link. I've been reading the Texas CDL handbook, which has a pretty good section on air brakes and it has some of the same tests.

[barmcd]

So, from reading the replies, I have a leak on the brake side since the air pressure bleeds off the air tank, but the suspension is good because the coach stays level when parked. It hasn't sagged a bit over a 30 day period of just sitting.