Air horn sometimes stuck on

Mako · 01-21-2023, 07:38 AM

Hello again everyone. New question for you. So my bus came with an air horn that is activated on the floor with a switch that looks exactly like the old school high beam switches. Any who, lately I have noticed when driving that after a certain air pressure buildup (usually after 115 psi) my horn will turn on and I have to press the switch, or tap the brakes to bleed the pressure down to get it to stop. Any idea why this is happening? is it perhaps I have an issue with the air system some where? It has happened a couple times in the past but pressing the horn switch usually fixed it and no other issues but recently, we went camping and both coming and going (each around a 2 hour drive) I had to relieve the pressure several times. It's very annoying and kind of laughable because people think I'm honking at them. We were in stopped traffic due to a vehicle fire and it went off and people thought I was getting mad at the situation. Any ideas on how to correct this? Also, I want to add switches or levers or something to relieve the pressure after driving. My big fat old butt can't get under the bus to pull the release valves. Any suggestions on how to do this? Thanks to you all for your continued advice.

rossvtaylor · 01-21-2023, 08:17 AM

Hi Mako, there are probably two parts to that system. The electrical switch that sends power to the coil on the air solenoid. The problem could be in the switch, which is keeping power on. Or it could be in the solenoid valve, which is leaking (or stuck) whether it's getting power or not. To diagnose which is the problem, you need to disconnect the power lead to the switch...or from the switch to the solenoid valve (sometimes called a Skinner valve). My guess is the valve is leaking.

To locate the air horn solenoid valve, trace the air pressure line from the horn back until you find the valve. This does mean getting under the bus, though.

I said "probably" because some buses don't have an electrical switch. Instead, the floor button is actually a mechanical valve. But since you said it looks like a high-beam switch, I'm guessing you have the electrical button. The mechanical ones usually have a larger "mushroom" head on the button.

For a quick fix, you could find the air horn and clamp a vice grip on the air line...just to stop air flow until you find what's sticking/broken.

fo4imtippin · 01-21-2023, 08:22 AM

Sounds like the valve that allows flow to the horn can't handle the high psl of your system. You can replace/adjust your governor to only build pressure to something lower like 110psi. Or you can replace the air horn valve (or an entire new horn system) with something that can handle the higher pressure.

Booyah45828 · 01-21-2023, 08:58 AM

Ross has you covered on the air horn. The valve is either electric or mechanical, and is likely gummy or weak, which is why it comes on errantly like it is.

As far as tank draining is concerned, you don't need to release pressure when parked, but to drain the tanks periodically they have cable operated self sealing valves that you can screw in place of your current petcocks. Here is one available from napa, most HD truck shops will have something similar.

https://www.napaonline.com/en/p/GRO8...&gclsrc=aw.ds&

Get some eyelets from the hardware store to hold the cable in place, mount the end somewhere accessible, and then whenever you want to drain moisture you just pull on the cable and do so. Here's a video of a guy installing them on a semi, you can attach your cables to the bus's skirting.

https://www.youtube.com/watch?v=IXK18QBPIgk

mmoore6856 · 01-21-2023, 03:32 PM

get a manual air horn valve , install it in your ceiling and put a string on it and be a real billy bob supertrucker

rossvtaylor · 01-21-2023, 04:14 PM

Quote:

Originally Posted by mmoore6856

get a manual air horn valve , install it in your ceiling and put a string on it and be a real billy bob supertrucker

I did that in my Ford cab-over. I like it so much, I might change over the Crown foot button.

https://youtu.be/9xeW530SJH8

mmoore6856 · 01-22-2023, 09:53 AM

Quote:

Originally Posted by fo4imtippin

Sounds like the valve that allows flow to the horn can't handle the high psl of your system. You can replace/adjust your governor to only build pressure to something lower like 110psi. Or you can replace the air horn valve (or an entire new horn system) with something that can handle the higher pressure.

remember if you take presure away you will lose volume and since your brakes need a lot of volume i would never suggest to lessen it

mmoore6856 · 01-22-2023, 09:55 AM

Quote:

Originally Posted by rossvtaylor

I did that in my Ford cab-over. I like it so much, I might change over the Crown foot button.

https://youtu.be/9xeW530SJH8

im converting my dimmer from the turn signal lever back to the floor where it belongs

fo4imtippin · 01-22-2023, 10:15 AM

Quote:

Originally Posted by mmoore6856

remember if you take presure away you will lose volume and since your brakes need a lot of volume i would never suggest to lessen it

I have heard of them going out and going up to 140psi or higher. I would only want to bring it back to spec and would rather mess with a horn than the air system.

Mako · 01-22-2023, 06:33 PM

Thanks everyone for the quick and informative responses. I was surprised when I found out I had an airhorn at first. I really love the ones that sound like a train. Maybe I'll just get one of those and and replace it with the one I presently have.

Mako · 01-22-2023, 06:39 PM

How many drain valves are there? I thought there were 2. Or is there just one tank?

rossvtaylor · 01-22-2023, 07:40 PM

Quote:

Originally Posted by Mako

How many drain valves are there? I thought there were 2. Or is there just one tank?

You could have as many as 4. 3 of them (the primary and secondary brake, and the auxiliary) could be on separate tanks or there are lots of baffled single tanks, which will have drains for each section. And in addition to those three, there may be another tank (first in line) as a primary collector. But you almost certainly will have 3 drain valves.

Truthseeker4449 · 01-23-2023, 12:07 AM

As an alternative to stringing cables, you can also run small air lines to tiny ball valves in a very accessible location. This arrangement is popular in transit buses and I've occasionally seen school buses with this arrangement.

And rather than messing with the system governor, install a regulator if pressure is a concern. The bus may have even come with a couple of regulators for the stop sign and crossing gate, repurpose one of those. A sticky valve or switch is more likely the problem, I've run into the same issue on rarely used pieces of specialty fire equipment.

Dbacks2k4 · 01-23-2023, 07:50 PM

Quote:

Originally Posted by mmoore6856

get a manual air horn valve , install it in your ceiling and put a string on it and be a real billy bob supertrucker

That's what I'm doing, kinda, haha. I'm going to install a switch off the horn button to select between the wussy prius "beep beep" horn (anyone else remember that Jeff Dunham bit??) or the newly installed massive air horn tied directly to the bus' air system.

I've encountered kids pumping their arms at my party buses before and there's always such a letdown on their faces when I hit the electric horn for them. My new rig is gonna rectify that

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