Parking Brake

[rtr6646]

Hi I have a 1998 Monaco Diplomat that will build up air with parking brake set,  but when it reaches 120 psi and I release the parking brake the low pressure beeper comes on again and the coach won't go forward or reverse-- like the brakes are still set, but, the brakes are released.

Ive checked them all and the air won't build up until I set the parking brake again. I can't hear air leaking anywhere under the coach.

Help.

Thanks

[kaypsmith]

The air brake canisters on the drive axel require air pressure to push against the spring contained within, this is what releases the parking brake. The fact that you are dropping air pressure to me would indicate that there is an air leak that is pretty large. If you can get close to the drive axel, not under the coach and clear of it's path in case of the parking brake releases, have someone in the driver seat, one that is competent enough to stop the coach just in case the parking brake does release, activate the PB release button, you should hear a rush of air to those canisters. If you do not hear that air rush and the pressure drops quickly as indicated, then you will need to find that leak, or possibly a bad actuator valve in the cockpit. At least that is where I would start to look for where is the air is going instead of to the DA brake canisters. You will find that once the air has depleted below the necessary pressure to work those canisters, the air will cease to try to go back there, therefore you will need some assistance in keeping up the air pressure to look for that leak, and this is in the event that you do not have an external source of air supply to keep that pressure high enough to hunt the leak. Good luck hunting! I should have added earlier, when was the last time you purged your air tanks?

[desertdeals69]

Yes be sure you tanks are dry.  It is possible that they are almost full of water which will reduce the air space and the volume of air used to release the brake uses up all your air.

[rtr6646]

 Thanks everyone the brakes finally let loose, Thanks again rtr6646

[kaypsmith]

What, if anything caused the brakes to release? Or were you just lucky? If you haven't purged those air tanks lately, be sure that happens soon, water builds pretty rapidly in hot humid weather. Glad you are back to moving again.

[rayin]

On 9/3/2019 at 9:35 PM, kaypsmith said:

What, if anything caused the brakes to release? Or were you just lucky? If you haven't purged those air tanks lately, be sure that happens soon, water builds pretty rapidly in hot humid weather. Glad you are back to moving again.

X2! When water gets into the air brake system things get expensive-and dangerous quickly. If chassis does not have automatic water ejectors, the manual tank drains should be pulled weekly for a MH.

[wolfe10]

???1998 Monaco without a built-in AIR DRYER???

Assuming it does have one, one should never get anything but clean dry air out of it.  If either water or particularly any powder (desiccant from the dryer) you are well past proper service interval for the air dryer.

[jleamont]

On 9/2/2019 at 6:17 PM, rtr6646 said:

Hi I have a 1998 Monaco Diplomat

Have you owned this coach since new? The reason I ask, have you ever heard the air dryer purge when the air gauge reaches 110-120 PSI?

When we bought our Monaco product I thought it wasn't equipped with an air dryer, turns out it was broken and the previous owner didn't like the noise when it purged so he built a wooden box around it. Once I discovered it by following the lines I replaced the dryer and removed the ugly modification. 

Based off of your initial issue, I believe you have a problem with the air brake system. Below is a test to perform to narrow down to which side of the system has an issue. At a minimum its a good test to get into a habit of checking for safety.

 Air brake safety devices vary. However, this procedure is designed to see that any safety device operates correctly as air pressure drops from normal to a low air condition. For safety purposes, in areas where an incline is present, you will use wheel chocks during the air brake check. The proper procedures for inspecting the air brake system are as follows: -

With the engine running, build the air pressure to governed cut-out (typically 100-125 psi). Shut off the engine. Turn on the key but do not start the engine, chock your wheels, if necessary, release the parking brake(s). Check the air gauge to see if the air pressure drops more than two (2) psi in one minute for single vehicles and more than three (3) psi in one minute for combination vehicles. - Then, fully apply pressure to the foot brake and hold for one (1) minute. Check the air gauge to see if the air pressure drops more than three (3) psi in one (1) minute for single vehicles and four (4) psi in one (1) minute for combination vehicles. If the air loss is greater, check for leaks and fix before driving the vehicle. You could lose your brakes while driving. - Begin fanning off the air pressure by rapidly applying and releasing the foot brake. Low air warning devices (buzzer, light, flag) should activate before air pressure drops below 60 PSI. - Continue to fan off the air pressure. At approximately 40 PSI to 20 PSI on a tractor-trailer combination vehicle, the tractor protection valve and parking brake valve should close (pop out). On other combination vehicle types and single vehicle types, the parking brake valve should close (pop out). - Check rate of air pressure buildup. When the engine is at operating RPM, the pressure should build from 85 to 100 psi within 45 seconds in dual air systems. (If the vehicle has larger than minimum air tanks, the buildup time can be longer and still be safe

[rtr6646]

Thanks everybody very good info Thanks rtr6646

[rayin]

FWIW, Meritor makes an air silencer for the air dryer system, and it's not a wooden box.