M923A1 air buzzer problem

[Randyw]

Need help finding my problem on my truck. The buzzer alarm constantly sounding on my truck and its driving me crazy. I first thought that the alarm was from the emergency break because it would come on then go off. But after taking a stroll today I noticed the alarm went off as soon as I took the emergency break off. When I left the house the alarm did not come back on until I got about two miles down the road. When it came on it stayed on the entire time. My air pressure stays around 100 to 120 pounds while driving and never drops below 90. My question is does the buzzer work off engine temp to? I do not have a heat light in my truck but the reason I ask is the fan has never come on while running the truck in the driveway. Temp gauge shows about 190 on the gauge but now I am wondering if I have a fan problem. When the alarm problem started I noticed the alarm would come on when the truck was running low speeds or idle. Once the truck was running at a good speed the alarm would go off. I have checked the grounds on the emergency break switch and all seems fine.

 

[Jericho]

Go to the Tech Data section on here and download the 5 ton Tech Manuals, its free and they are worth their weight in gold, The buzzer is a PITA , is wired into the brake handle in the form of a micro switch way down in side the handle and then its daisey chained to the tank low pressure switches and the spring brake switch/ bypass valve in the dash . All of the switches for the tanks and spring brakes are the same , Been fighting with mine for a while the buzzer its self is in the Protective control Box. look for air leaks around the sending units, they are two wire units , red the book , shoot the wires to look for continuity , doesn't really matter which leads you connect , its a pressure reached completed circuit . Read the trouble shooting, you looking for a "to ground" if I remember right when the circuit is completed. but iam old so read the BOOK get a good multi meter !

 

[Jericho]

Temperature has nothing to do with the buzzer, they run cool and the only time the fan will engage is when the temp gets up to the 200 to 210 range , it is controlled by the shutterstat, which is mounted on the top of the engine in a boss on the rad hard line. they are not cheap run 195 to 300 $ when the fan kicks in YOU WILL HEAR IT IT ROARS , all in the manual , so grab a soda and read, you will enjoy it and increase your knowledge .

 

[98G]

Some of the A1 trucks had a motor temp warning light. I don't believe it had an audible component.

 

[74M35A2]

Is the low air light on? Let the truck sit overnight. Air will probably bleed down and be below 60psi (alarm point). Start cold truck, have parking brake off, and see if the alarm stops at 60psi and cold engine.

G could be onto something. As these trucks age, sensors can fall out of calibration. This is really common on CTIS components. So, even though your truck may not be overheating, the sensor, if it has one, may think so.

The spring brake override switch (mushroom button) should not set a buzzer alarm regardless of position. It should just illuminate the dash warning warning lamp when pushed, meaning the spring parking brakes will not set when the parking brake handle is pulled.

 

[Jericho]

74 is correct. The spring brake ivertide itself won't sound the alarm. But carefully observe your warning light for parking brake has it got a slight glow or does it light. My parking brake and buzzer problems. Have usually started with a slight illumination of the warning light then the buzzer. By the way ism talking about an A2 but reqardless the trouble shooting is in the T. O.

 

[Randyw]

Go to the Tech Data section on here and download the 5 ton Tech Manuals, its free and they are worth their weight in gold, The buzzer is a PITA , is wired into the brake handle in the form of a micro switch way down in side the handle and then its daisey chained to the tank low pressure switches and the spring brake switch/ bypass valve in the dash . All of the switches for the tanks and spring brakes are the same , Been fighting with mine for a while the buzzer its self is in the Protective control Box. look for air leaks around the sending units, they are two wire units , red the book , shoot the wires to look for continuity , doesn't really matter which leads you connect , its a pressure reached completed circuit . Read the trouble shooting, you looking for a "to ground" if I remember right when the circuit is completed. but iam old so read the BOOK get a good multi meter !

Thanks Jericho I will print out the manuals and do some trouble shooting.

 

[Jericho]

Your lucky if you could still have 60 psi overnight. !!! I've beenleak chasing for months. Never would keep any pressure overnight. One more air in the stack valve to go e

 

[Randyw]

Is the low air light on? Let the truck sit overnight. Air will probably bleed down and be below 60psi (alarm point). Start cold truck, have parking brake off, and see if the alarm stops at 60psi and cold engine.

G could be onto something. As these trucks age, sensors can fall out of calibration. This is really common on CTIS components. So, even though your truck may not be overheating, the sensor, if it has one, may think so.

The spring brake override switch (mushroom button) should not set a buzzer alarm regardless of position. It should just illuminate the dash warning warning lamp when pushed, meaning the spring parking brakes will not set when the parking brake handle is pulled.

The low air light is not on. The light goes off as soon as I take the brake off set. Like I said the alarm may not sound until a few miles down the road but once the alarm comes on it stays on. I will try to start the truck with the emergency break off and cold engine and see what happens. I will post back tomorrow what the outcome is. Thanks for you guys help.

 

[98G]

When the alarm comes on, it pulses somewhat also?

 

[Randyw]

When the alarm comes on, it pulses somewhat also?

No it does not pulse. Just a steady alarm.

 

[Randyw]

Ok guys, I did a cold start driveway test this evening to see if I can figure out this buzzer alarm.


I fired the truck up with out the emergency break set at 1800.

When I fired the truck up on cold start the air pressure gauges showed 80 PSI both primary and secondary.
The oil pressure at start up was 85-90 and I had no alarm at all.

The truck idled until 1848 and that's when the buzzer alarm came on. No alarm indication lights

When this happened the air pressure was at 120 on primary and 110 on secondary.
Temp gauge showed 160 degrees.
Oil pressure was 65-70

I continued to let the truck run until 1905 and the alarm constantly sounded. When I shut the engine off the temp was at 190 degrees with 60-65 on the oil pressure.

I have checked ground wires in the emergency brake handle and also on the black box just under the dash that looks brand new. I have no idea what is causing this.

 

[98G]

There's 2 low air sensors. I suggest replacing both of them.

Also, probably your whole air system has moisture in it. Plan on a PPV soon, and likely an air drier.

 

[Randyw]

There's 2 low air sensors. I suggest replacing both of them.

Also, probably your whole air system has moisture in it. Plan on a PPV soon, and likely an air drier.

98G, Where are the 2 low air sensors located and where can I get new ones to replace them?

 

[98G]

https://www.steelsoldiers.com/showthread.php?110768-Low-air-pressure-light-buzzer-inop-on-M923

Edit to add pic -

 

[74M35A2]

Could be the overheat sensor you mention, since no warning lights are on. Low air should trip a dash light. Find the possible overtemp switch on the engine and unplug it, retest. I don't know where this is.

 

[98G]

Could be the overheat sensor you mention, since no warning lights are on. Low air should trip a dash light. Find the possible overtemp switch on the engine and unplug it, retest. I don't know where this is.

I disagree. The overheat sensor was a light located in the same row as the rest of the warning lights. (I've only seen these on A1's)

I'd bet a lot that it's the low pressure sensors, one or both.

 

[Jericho]

if the system is the same, I think it is, there are 3 pressure switches, primary secondary tanks on right hand passenger side , easy to identify two wires in, and one the right hand side of the spring brake valve handle behind the dash panel , can be changed easy with out pulling dash, just shimmy up under , its easy to do ops checks on them, its in the T.O. Emergency brake handle is a two wire as well wires drop down thru the handle penertration in the floor, look for shorts

 

[74M35A2]

Sorry, I mis-read your earlier post. I should probably just stay out of 250 engine posts huh?

 

[Jericho]

Good call 98 sounds like a sensor or a chafed wire short. BUT post the results please !