air pressure gauge alarm

[Larry Barch]

The air pressure gauge alarm on the dash of my 2000 Marquis continues to sound. Both the red needle and the green needle are reading 120psi. what do I need to do to silence the alarm correctly.  In the past the alarm shut off around 90psi as it was building to that 120psi mark. Thanks, Larry

[Pat Long]

Have you checked the air pressure diaphragm at the brake release knob?  It would  be attached under the yellow knob itself, either behind the dash or left side panel depending on models.

[Gerald Farris]

Larry,
I have never seen this problem before, but the alarm should be triggered by an electrical pressure switch. So your problem will be caused by a defective switch or a shorted wire. If you can locate the switch (probably under the front cap), disconnect it and if the alarm stops, it is a bad switch, otherwise you start tracing wires.

I am in Bend Oregon now, and I will be at BCS in a few days, and I will find out the location of the switch, and any other common causes for you problem.

Gerald

[Larry Barch]

Thanks Gerald, any help would be appreciated. What do you mean by the front cap. Are you talking about the compartment on the top of  the dash leading to instruments?

Larry

[Gerald Farris]

Larry,
The front cap is the front fiberglass section that the windshield is mounted in. When someone refers to the area under the front cap they are referring to the area between the front of the coach and the firewall. The firewall is the where the dash section starts as you move from the front of the coach going back.

Gerald

[Gerald Farris]

Larry,
I went to BCS yesterday to discuss your issue with the techs. Since the alarm for low air pressure and parking brake both sound almost identical, you need to determine that your issue is the low air pressure alarm. This can be verified by the corresponding warning light should also show on the dash when the alarm is sounding.

The low air pressure warning switch should be inline just behind the instrument cluster. It is a normally closed switch that opens at 60 PSI. If the low air pressure warning is your problem, you can just disconnect a wire at the switch to silence the alarm. However if your problem is the parking brake alarm (more common), the switch for it is located on the parking brake control (yellow knob).

Gerald

[Dave Atherton]

Larry, the air alarm is a safety feature that would recommend not to operate or drive with
Air buzzer sounding. First the two indicator needles on gauge will read air pressure going
to your front brakes and one needle will read air pressure to your rear brakes. The reason
for air buzzer sounding alarm at around 60 psi. Is to warn the driver there is a problem within
the air system and engine air compressor cannot meet demand to maintain air pressure. What
happens next as air pressure drops to 50 psi on the air gauge your rear axle has what is called
spring brakes or ( maxi brakes ) that will apply with low air, pressure and lock up your rear brakes.
The rear brakes will not release until air pressure builds back up to over 60 psi.
Dave Atherton Retired Cat Mechanic

[Mike Tomas]

...what is called spring brakes or ( maxi brakes ) that will apply with low air, pressure and lock up your rear brakes.
The rear brakes will not release until air pressure builds back up to over 60 psi.

Dave. I'm a Class B driver with experience with air brakes. My 2000 Patriot Thunder (Safari) has what is called Air Over Hydraulic brakes (I'm not personally crazy about them). My question Dave, is this system, still a "Positive" braking system where the brake pads are normally clamped down on the rotors and the hydraulic pressure releases them from the rotors? Do they work the same as you are stating above? Or do they work like cars, where Hydraulic pressure presses the brake pads to the rotors to brake?

The second part of the question is: I know the Parking brake is just a rotor and caliper located on the drive shaft. When The parking brake is engaged, does it also engage the pads to the rotors on all four wheels?

being that Larry has a 2000 Marquis (Safari) Might they also have Air-Over-Hydraulic brakes? and BTW Larry, you don't want to silence the alarm, even if temporarily. you do what to fix the real issue, which may be a leaky hose to the pressure sensor, the pressure sensor, or an electrical issue with the air pressure alarm circuit. That alarm, as annoying as it is, is a VERY important warning device designed to alert you while your driving "something is wrong, pull over NOW (less than immediately)."


Signed,
Wishing I had real air brakes.

[Gerald Farris]

Mike,
Your 2000 Thunder has hydraulic brakes that operate just like the brakes on a car. The only difference between the base brakes on your coach and a 4 wheel disc car is that your coach uses air pressure to provide extra assist where a car (gasoline powered) uses a vacuum booster to provide the assist. Your parking brake only consist of the caliper and disc located on the drive shaft, and it does not have any connection to or control over the wheel brakes. It is spring applied and air pressure release, so it operates just like a parking brake on an air brakes system.

The 2000 Marquis has a Meritor ADB all wheel air disc brake system. The 2000 Marquis wheel brakes are applied by air pressure through the air chamber (air can) at each wheel or dual. The 2000 Marquis parking brake is spring apply and air release, and it applies the wheel brake on both sets of drive wheels when engaged (no air pressure). 

Gerald