Help with air brake issue, please

[Garage Monster]

My air system has the usual twin needle pressure gauge.

First question is the white needle for front or rear brakes?

While driving the red needle barely moves and stays pretty steady at about 120 psi. The white system has a slow leak and will slowly drop about 5 pounds and the rise back up. Occasionally it will drop 20 pounds or more and then quickly rise back up. When climbing long grades it has a few times dropped to the point of the warning buzzer coming on. If I quickly snap then throttle off and on once or twice it will catch and rapidly come to back 120 psi.

Can somebody tell me where the faulty valve or regulator might be found on my 93 Monaco, what is the proper name for it, perhaps send a picture so I know what I am looking for, tell me where to look for a new one and anything tips on replacing it?

That is a big request, I know, but I am looking for knowledge and this forum is a gold mine of knowledge. I am headed from Washington to Colorado so I hope to make the change myself. I will check back in tonight when I stop for the day.

[Chuck B 2004 Windsor]

FWIW, I have not seen many 93 Monaco CRSS coach owners on this site.  I hope someone who has one will chime in and help.

[BradHend]

I only have an air emergency/park brake on my coach with the 4 air bag suspension system (R4R) and I’m not sure exactly where your pressure is going while climbing a hill. 
I do know however, that your red needle is your primary air tank, which serves your main rear brakes (up to 80% of your braking power), and the white needle is your secondary tank which serves your front steer axle brakes.  Your secondary tank is usually also for accessories such as the seat, air horn etc.  Might be time to get the spray bottle with soapy water and start checking over your system as the leak could be anywhere.  Be careful, if you get under usually 50PSI in either of your tanks, your emergency brake will set.

[Garage Monster]

Thanks. When I get to my destination I will do the soapy water thing and see if I can find the leak. The leak is very minor my main concern is I don't understand exactly what triggers to refill that tank and what it looks like and where to find it underneath the coach. That is what I'm hoping to find out

[Frank McElroy]

I can't speak for 1993 air brake systems, but on coaches like mine, the parking brake will stay released if either tank is above the minimal pressure.  The reason this works is that both air tanks feed the parking brake valve control module.  This is how air gets balanced between the two air tanks and it's what allows you to dive to an area where you can safely pull over or drive to the next exit before tank pressure in your good tank falls below minimal pressures to keep the parking brakes released.  But this valve has air flow limiting check valves that would prevent air from draining both tanks through the parking brake valve should either a primary or secondary system fail.

This can be easily tested by dumping air from the primary or secondary air tank and the other tank still pressurized should keep the parking brakes released.

If the 1993 braking systems are like mine, it's troubling that one tank drops in pressure but the other one doesn't.  I've seen parking brake control valve modules fail where when you drain one of the air tanks, the air passes through this valve to drain the other.  Check to see if you have this valve on your coach and if so, test it.

Do you have an air operated throttle?  If so this is where you are likely losing air under full throttle due to an air leak.  So, lets say you have a major leak in an air throttle system, the parking brake valve control module flow limiting check valves would kick in and isolate your primary and secondary tanks.  That would explain why one tank drains air and the other tank doesn't.

Here is a link to a number of file documents that you might find useful.  I'd start with the Bendix Handbook that should help you in identifying the components that you have on your system.

In addition to the above information, I did a search of our parts list.  It would be good for you to download the parts list and using Acrobat Reader (not a web browser) do a search of this list for Throttle and a separate search for Royal.  Lots of parts information in there. 

As suspected, circa 95/96 Monaco converted from an air throttle to an electronic throttle.  Info is included in our parts list.  Link below is attached.

 

 

[CRY1942]

Hello:

"

11 hours ago, Garage Monster said:

I don't understand exactly what triggers to refill that tank and what it looks like and where to find it underneath the coach.

If I understood your question, the D-2 Governor is what controls the start and stop of the Air Compressor by monitoring air pressure in the front tank. Most likely located near the engine driven Air Compressor.

A very common leak point on the front air tank is the Pressure Protection Valves (PPV) recently replaced all three of mine due to two leaking.

Attached is a generic drawing of a typical air system.

 

[jacwjames]

Last year prior to a trip I did an air leak test monitoring how long my air system would stay up.  It stayed above the low alarm level for days.  I also took a bottle of soapy water and sprayed everything down and didn't find any leaks. 

Later in the year after 2 trips with coach I noticed my air dropping overnight to where the low air alarm came on when I turned on the key in the AM.  So I started to monitor, it got progressively worse.  I crawled under the coach with a bottle of soapy water and was surprised when I found all the Pressure Protection Valves leaking.  But based on feedback from members of the Moncocers & IRV2 forum I decided I was OK since my air would build quickly and stay up while driving.  So I continued my trip but then one day after I parked for ~30 minutes the low air alarm came on when I turned the key.  Started to get really concerned.  I tried to find a shop on the road with no luck so finally just decided to head home and spent the next couple weeks working on the air system.  Replaced all the PPV's along with similar type check valves.  Not hard and I gained knowledge on my air system.

I found the attached document on troubleshooting an air system  It might help.  I think Franks comment on the air throttle (if you have one), might be valid since your problem occurs on hard pulls.  Just something to look at.

air system trouble shooting.pdf

[Frank McElroy]

On 9/6/2022 at 6:37 PM, Garage Monster said:

My air system has the usual twin needle pressure gauge.

First question is the white needle for front or rear brakes?

While driving the red needle barely moves and stays pretty steady at about 120 psi. The white system has a slow leak and will slowly drop about 5 pounds and the rise back up. Occasionally it will drop 20 pounds or more and then quickly rise back up. When climbing long grades it has a few times dropped to the point of the warning buzzer coming on. If I quickly snap then throttle off and on once or twice it will catch and rapidly come to back 120 psi.

Can somebody tell me where the faulty valve or regulator might be found on my 93 Monaco, what is the proper name for it, perhaps send a picture so I know what I am looking for, tell me where to look for a new one and anything tips on replacing it?

That is a big request, I know, but I am looking for knowledge and this forum is a gold mine of knowledge. I am headed from Washington to Colorado so I hope to make the change myself. I will check back in tonight when I stop for the day.

Robert, in addition to my other posted info, offline I've been talking with with David (dl_racing427) who owns a 1983 Dynasty.  His coach does have an air throttle and described the procedure he would use to determine if air leaking from this system is the reason why you are losing air from your front secondary air tank.  He asked me to post the following for him.

 

That should be pretty easy to troubleshoot.
Just build up the air, shut down the engine and step on the throttle pedal.
Air pressure should drop very slightly and then hold steady.
If it continues dropping, have someone hold the pedal down and listen for a hiss in the engine bay, and forward along the air line from the diaphragm to the pedal valve.